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1. ES ES mH EE x E ch cho tet bt pH EE EE HEU EE pp RII 5 Tcp Se __ lt lt _ PEE HERES teed ie _ Dese optet oett prato eura 5 55 5 SS SS lt T meme mem S oe 25 Ss _ _ i iu ATTE tone EEEE o ee _ aa ee ee petted SSS SV Toto T SE SS SS ee iN TERT oen a es Es Se pea 10 inch 1 inch 106 IV
2. Mdt M Head inches 1 2 3 4 5 6 7 E dicens 500 550 600 650 S m 5 06 HEHH i Yj 2222 D QW ee RQ ees T LU VY 17 AWC e 2 2 o m B 50009001 000025 Yj YY 10 15 20 25 30 40 60 Table IV 2 gives the suggested minimum diameter gates for full open and completely submerged conditions see Fig IV 17b 102 TABLE IV 2 MINIMUM RECOMMENDED DITCH GATE SIZES FOR SURFACE IRRIGATION SYSTEMS uu ME M 2 065656 Head inches 05 08 10 12 14 16 6 EN qum 8 H 3 m 10 777 SUO 12 ssec 1 UP 5 aan E _ 2 M 2 4 o EE _ jj m B NE E SS ES 3 an 2 22 m The sizing of large ditch gates like the border basin gates illustrated in Figure IV 16 can be considered similarly to check outlets when at the maximum flow the gate itself 1s raised above the water surface specifical
3. 68 Figure 11 Advance recession curve for the example FreeDrainingFurrow_2 cfg Apr X E 74 Figure III 12 Tailwater hydrograph for the example FreeDrainingFurrow 2 data E 74 Figure III 13 Corrected advance recession curve for FreeDrainingFurrow_2 cfg data M 75 Figure III 14 Corrected tailwater hydrograph for FreeDrainingFurrow 2 cfg data 75 Figure 15 Final simulated tailwater hydrograph for FreeDrainingFurrow 2 cfg Odd ocv D Ra E M S 76 Figure IV 1 FreeDrainingFurrow 1 advance recession trajectory 83 Figure 2 FreeDrainingFurrow 1 tailwater hydrograph 83 Figure IV 3 Soil moisture distribution from FreeDrainingFurrow 1 data 84 Figure 4 SURFACE Design Panel for initial FreeDrainingFurrow 1 condition 84 Figure IV 5 Improved design for initial irrigations ecce ecce eee e ee eeeee 85 Figure IV 6 Selecting the later irrigation conditions ee eee eere eee eene 86 Figure IV 7 FreeDrainingBorder 4 advance recession plots for initial irrigations Hunden IRL UII UII 87 Figure IV 8 Tailwater hydrograph for FreeDrainingBorder 4 data
4. D e Fo 0000786 0001981 0003369 00042704 0005974 0007212 0008396 0009548 0010656 0011733 0012777 0014768 0016652 0018417 0020096 0021679 0028384 0033508 0044606 Fo 0000624 0001582 0002702 0003757 0004779 0005769 0006717 0007632 0008525 0009386 0010215 0011819 0013315 0014736 0016071 0017341 0022712 0026802 0035693 Continuous Flow Intake Curve Parameterz for Later Irrigations Continuous Flow Intake Curve Parameterz for Initial Irrigationz ft Wpr ft 55 TABLE III 5 SURGE FLOW FURROW INTAKE FAMILIES INITIAL IRRIGATIONS Surge Flow Intake Curve Parameterz for Initial Irrigations ID 5011 Fa Wpr ft J ft man a t 3z Etz mn ft Heavy Clay Clay Clay Light Clay Clay Clay Clay Loam Loam Loam Silty Silty Silty Silty Silty Silty Sandy Sandy Sandy Loam Loam Loam Loam Loam Loam Loam Sandy Sandy 002120 003906 005973 007620 009046 010327 011500 012586 013623 014591 015520 017270 018891 020422 0218
5. ecce ee ee eere eee eee eee eee eee eee 18 Figure I 15 Advance and recession trajectories for a surge flow system 19 Figure 1 16 Early surge flow system eee e eee ee eee e e reete e eee ees e eee e etes eee 20 Figure 1 17 The automated butterfly surge flow valve 21 Figure 1 The main SURFACE SCEGRU Ned hn aee ua aUas Ee 23 Figure 2 The SURFACE command eee ee e e eere eee eee ettet 23 Figure 3 The SURFACE input tabbed notebook 24 Figure 4 The SURFACE tabular output screen ecce ee eee eee eene 25 Figure II 5 The Field Characteristics panel of the input tabbed notebook 26 Figure II 6 Illustration of multiple sloped surface irrigated field 28 Figure II 7 The Infiltration Characteristics panel of the input tabbed notebook 30 Figure II 8 The NRCS reference intake family for initial continuous flow furrow IEEIPQUOTS ico noi ET PM 3l Figure II 9 The Inflow Controls panel of the input tabbed notebook 32 Figure II 10 The Hydrograph Input panel of the input tabbed notebook 35 Figure II 11 A typical advance
6. 78 IV 2 THE BASIC DESIGN PROCESS 79 2 1 The Preliminary 79 IV 2 2 Detaled BI T m m UNTER 80 3 BASIC DESIGN COMPUTA TIONS 81 IV 3 1 Free Draining Surface Irrigation 81 IV 3 1 1 Example Free Draining 1 1 2 2 6010 0000000000000000000000 nnns 62 IV 3 L2 Example Free Draining Border peli t denen petet Denies A 86 IV 3 2 Blocked end Surface Irrigation sse eene nennen nne 88 IV 3 2 1l Example Blocked End Border ebore hen pa Eres Op e s 90 IV 3 3 Design Procedure for Cutback Systems sssssesessssseceesseseseseessesesssssesesesssesesssssecensesseesecs 91 IV 5 3 1 Example Furrow Cutback DESIO n iaces e ea pen p e Essi 91 IV 3 4 Design of Systems with Tailwater o det 93 IV 3 4 Example Furrow Tailwater Reuse 95 IV 3 5 Surge Flow S VSIE 96 Example Surse blow 97 4 HEADLAND FACILITIES 98 4 1 Head Rem 98 uude Siphon Tubes and
7. 42 43 IRAS Printed OUMU 43 EES SAMPLE SEES 43 essem seem ein me sem RM E 43 IL5 20 M ERI 43 iBreeDramine Border SCi arii a 44 sA BreeDraimine Border ER RENE 44 ILS Blocked ndiorder c te eder INNER ER AIRMAN T EE 44 Bash op cr 44 ESAME UN NOTER E DNE OH 45 LL aM AE 45 SURFACE IRRIGATION EVALUATION 46 INTRODUC TION 2525 0E PEE UO EOS S aaa 46 2 SOME IMPORTANT SURFACE IRRIGATION 5 1 46 III 2 1 EP 46 o ence cds i 50 DE ho Bgm 50 III 2 2 DAE DACA Rc 51 51 1 2 2 2 Revised NRCS Intake Families ciscus
8. 87 Figure IV 9 Design Panel for the final design of the FreeDrainingBorder 4 initial example di och t 88 Figure IV 10 Stages of a blocked end irrigation e eee eere 89 vi Figure IV 11 Figure IV 12 Figure IV 13 Figure IV 14 Figure 16 Figure IV 17 Figure IV 1 Figure IV 19 Figure IV 19 Figure IV 20 Simulation of the BlockedEndBorder data 91 Simulated tailwater hydrograph using the CutbackDesign cfg data file 92 Schematic tailwater reuse system e eeeee eee eee ee eee eee eee esee ess eee eeeeeus 94 FreeDrainingFurrow 2 cfg design of the field using the main water SUDDIV ieri EH HE nn I nS 96 Typical surface irrigation head ditch configurations 100 Typical operational conditions of surface irrigation siphons and spiles 102 Typical head discharge curve for gated pipe outlets 105 Layout of FreeDrainingFurrow 1 gated pipe system 107 Layout of FreeDrainingFurrow 1 gated pipe system 108 Alternative gated pipe layout for FreeDrainingFurrow 1 109 Figure A 1 Comparison between the average 6 hour intake rate and the basic intake rate of the
9. UE 101 Mek tall estie ieu 101 IV 4 1 Sing Check Outlets and Large Ditch 101 IV 4 2 Gate d DIDESDESIBINOEO GE utente tM cic oeste eei 103 IV 42 1 Choosing a Pipe Material n sc 104 104 1 429 aed PPE SIZHD tonta 105 V424 Example Gated Pipe DESIPD s oc ete pei ona 107 IV 4 3 Comparing Alternatives for Headland Facilities 109 APPENDIX A NOTE ON THE DEVELOPMENT OF THE ORIGINAL NRCS INTAKE FAMILIES AND THEIR MODIFICATIONS FOR FURROW IRRIGATION dan imm 111 INTRODUCTION 5 uoi tvi iab ds cecus 111 2 EVOLUTION OF THE ORIGINAL 111 MODIFICATIONS FOR FURROW 1 2 e etae tasse esee 112 4 MODIFICATIONS FOR BORDER BASIN AND FURROW 113 Acad NRCS nake Famy Om att a 113 A 4 2 Adjusting Intake for Furrow Irrigated 5 114 A 4 3 X Converting Between Bo
10. SURFACE Surfers Evaluation Design and Simulation Program urlace X Sulisurface Flow Simulated System Performance Outlow Runoff Hydrograph Advance Time min 522 Applic tion ETficienicy 62 2 Require mt Efficiency 99 67 75 1 ms Figure 14 The main simulation screen There are three important regions in the simulation screen The first occupies the upper 36 two thirds of the screen and plots the surface and subsurface movements of water as the advance and recession trajectories are computed The target or required depth of application 15 plotted as Zreq SO that when an infiltrated depth exceeds this value the user can see the loss of irrigation water to deep percolation The subsurface profile color changes as the depth exceeds 2 4 In the lower right side of the screen a summary of the simulated irrigation event will be published after the completion of recession The uniformity and efficiency terms are defined later in Section III The bottom four edit windows give a mass balance of the simulation including an error term describing the computed differences between inflow infiltration and runoff 1f the field 1s not diked As a rule an error less than 5 15 acceptable most simulations will have errors of about 19 In the lower left side of the Runoff Hydrograph screen a runoff hydrograph will be plotted for the cases where downstream
11. 46 L m m L t t i L j a III 47 where t the time of recession at a distance x from the field inlet min t time of recession at the field inlet sometimes called the time of depletion min time of recession at the field midpoint min and t time of recession min The intake opportunity time t at any point x 1s defined as 48 69 3 1 4 Example In the example data set labeled FreeDrainingFurrow_2 cfg field data are reported for advance and recession measurements the Hydrographs Inputs panel of the input tabbed notebook Calculate the advance and recession curves for this field evaluation The advance curve represented by Eq 41 15 determined as follows The advance time to the midpoint of the field given by the station at 1013 feet is 116 0 minutes and the advance time to the end of the field at 2050 5 feet 15 352 7 minutes These numbers are show under button on the infiltration characteristics panel They are also indicated in the Advance and Recession spreadsheet on the hydrograph inputs panel The inflow is shutoff at 1440 minutes The time of depletion f at the inlet is 1444 minutes as shown at the recession time in the hydrograph inputs panel The time of recession at 1013 feet along the furrow is 1482 minutes and the recession time at the end of the furrow f is 1502 minutes The value of r from Eq III 42 15 The
12. 500 an 1000 1100 1220 1300 1 220 1500 1608 1700 1508 1900 Distance along 1018 feet Figure III 13 Corrected advance recession curve for FreeDrainingFurrow 2 data una Rate ete gt Time Dans Figure III 14 Corrected tailwater hydrograph for FreeDrainingFurrow_2 cfg data 75 The volume balance procedure calibrated the intake parameters so they produced accurate simulation of the advance trajectory but under estimated the volume of tailwater indicating that the value of F is too large To adjust the calibration so both the advance trajectory and the tailwater hydrograph are simulated accurately reduce the value of F by trial pu and erro click on the to adjust a and K with each F trial and then re run the simulation When the value of F 1s about 0 00025 ft ft min ais 0 3273 and K is 0 01432 ft ft min the advance fit will appear like Fig 13 and the tailwater plot like Fig 15 Bali am am E ga 1 Flapand Time Maya Figure 15 Final simulated tailwater hydrograph for FreeDrainingFurrow_2 cfg data 3 2 4 Adjusting Infiltration for Furrow Wetted Perimeter Three situations exist that may require an adjustment of the infiltration parameters a k and fo or a and The first is when values from Tables II 3 III 6 need to be adjusted to distinguish between furrow and border basin
13. of Surges By Target Application zreq Inflow Hegime Control Continuous Inflow t Continuous Inflow w Cutback Continuous Inflow Hydrograph C Fired Cycle Surge Flow Fixed Cycle Surge Flow Cutback VYanable Cycle Surge Flow Variable Lycle Surge Flow w Cutback Simulation Speed Graphic Profile Slope a Hun Parameters Simulated Unit Inflow Ips Time of Cutoff mn mn of Surges Surge Cycle On Time mn Cutback Ratio CB Length Fraction Surge Ad Ratio Surge Adj Time mn LF 240 0 1 00 1 30 0 1 00 1 0 1 00 0 00 0 10 Figure 9 Inflow Controls panel of the input tabbed notebook 32 4 3 1 Simulation Shutoff Control The basic cutoff or shutoff for surface irrigation system occurs when inflow to the furrow border or basin 15 terminated at the field inlet Unlike drip or sprinkle systems in which this represents the end of the water applications surface irrigation systems have a continuing or recession phase that can depending on the type of system and its configuration involve a significant application of water to parts of the field Time of Cutoff mn The termination of field inflow for the purposes of software execution is defined by two check boxes and an input box Time of Cutoff Under the heading Simulation Shutoff Control the user must select either to terminate inflow at a specific time By Elapsed Time o
14. Dischage id Pty Run Length ft 2080 Design Flow Hesults Hn of Sets 0 023 Application Efficiency X 74 46 3 Irmigation Efficiency X ff 38 Hequirement Efficiency 99 01 1 Distribution Uniformity 5 94 90 Tailwater Fracton 20 26 Deep Percolation Fracton 5 28 Samdate Design Jan Pate ane Firs Fane Figure 14 FreeDrainingFurrow_2 cfg design of the field using the main water supply 96 There are two critical design and operational rules for surge flow systems First the surges applied to the field during the advance phase should not coalesce 1 e the advance front of one should not catch up and merge with a preceding surge The second rule 15 that at the end of advance when cutback 1s desirable the opposite should be facilitated each surge should coalesce or merge The hydraulics of surges that do not coalesce behaves very much like the hydraulics of continuous flow at the same discharge whereas the hydraulics of coalesced surges behaves very much like a cutback discharge Thus in the same irrigation management regime are the means to expedite rapid advance to minimize deep percolation as well as an effective way to implement cutback to minimize tailwater runoff during what some call the soak cycle 3 5 1 Example Surge Flow Design The FreeDrainingFurrow l cfg file was used in mulated System Performance section IV 3 1 1 t
15. ea 7 1 2 2 4 Water SUPP anir 8 1225 E E 8 1 2 2 6 CODINA ee ien ded 8 1224 CUO 8 1 2 2 8 NER dn 8 pac ASOLO CR Ui cc ER 9 1 2 3 1 Development COS ee ee 9 12 32 Iac OMIA eU te ED 10 1 2 3 3 Seene ee 10 1 2 3 4 M dico SUD 10 1 2 3 5 RR 10 1 2 3 6 11 2 3 7 E mem 11 1 2 1 8 Land Gove X 11 1 2 4 summary of Surface Irrigation 12 13 WATER MANAGEMENT IN SURFACE IRRIGATION 5 8 4 12 1 3 1 Choose a Sutface Ireablor SySteim bet 13 13 2 Inlet Discharge Control 5 a 13 1 3 3 Chaneing the Field Geometry and Topography 14 1 3 4 Recovery and REUSE 14 1 3 5 Automation and Equipment esce ER PR REPRE 15 I 3 5
16. 53 III 2 3 Irrigation Efficiency and Uniformity 60 H7 T drpipalion Us esos 61 1 2 32 Applicaton ETCEN Y 61 M233 Storage or Reguirement EMCIENC Y ure edu 61 WoA 61 ADE SP Percolation RI 62 62 62 2 4 IWICASUT CMI 63 EEE DE VALUATIONS 64 III 3 1 Standard Field Evaluation PLO CCG UE i 64 NOW Ebr 64 n RII 67 Advance ANG RECESSION 68 WESA ESIP 70 III 3 2 DN mU 70 Volume Balance 71 3 2 2 Volume Balance Estimate of Kostiakov and T2 73 1 3 2 4 Adjusting Infiltration for Furrow Wetted Perimeter 0 0 76 ILS 25 COBIICH TI IV REDESIGNING SURFACE IRRIGATION SYSTEMS 78 IV 1 THE OBJECTIVE AND SCOPE OF SURFACE IRRIGATION
17. Vu TW Zr WL 4 in which the wis greater than 1 0 to allow for some deep percolation losses leaching If for instance the value of w is 1 0 foot and with L and also in feet then 15 ft If a blocked end system could apply uniformly it would also apply water with 100 application efficiency Although a blocked end system obviously cannot do so the designer should seek a maximum value of efficiency and uniformity Since Eq IV 4 represents the best first approximation to that design it 1s at least the starting point 1n the design process Given that the inflow will be terminated at tco the inflow rate must be the following to apply to the field 0 IV 5 The procedure for selecting 4 for blocked end systems given above is very simple yet surprisingly reliable However as one s intuition must surely warn it cannot work in every case and needs to be checked by simulating the results with the SURFACE software The risk with the simplified procedure is that some of the field will be under irrigated and thus using Eq IV 5 to select a flow rate rather than a more rigorous approach will be conservative 3 2 1 Example Blocked End Border Design Open the file BlockedEndBorder cfg and examine the input data The target application depth 1s 3 inches and with the intake coefficients given will require an intake opportunity time of nearly 312 minutes for initial irrigations and 441 minu
18. many values and need to be computed from the cross sectional measurements of Tmax Base and The SURFACE program does this by numerically integrating the furrow shape On the lower center of the Field Topography Geometry notebook is a Manning flow Manning Equation Calculator calculator shown here Once the basic shape has been M defined by the unit width for borders Tinax Base P and Ymax for furrows the user can enter a slope a Manning Manning n 0 0400 n and a flow The Manning calculator will then compute Flow gpm 32 0000 the depth of flow j E Depth ft 0 23760 wetted perimeter the user enter the slope Peps Ix 0 0924 Manning along with any one of the other variables such as area and the remaining others will be determined The Top Width ft 0 6348 Manning calculator will assist the user in evaluating border Wetted Perimeter ft 0 8262 and dike heights checking whether or not the furrow has overflowed due to the flow or blocked end or to determine what the maximum flow could be without breaching the border dikes or furrow perimeters The Manning calculator can also be used to approximate the conditions in open channel field ditches It should be noted that the procedures were written for irregular shapes like typical furrows and are only approximate for the regular trapezoidal shapes To use the calculator or field ditch evaluation and design set th
19. An expression relating wetted perimeter WP can be defined as a function of flow depth y as follows WP y y 27 where and are numerical fitting parameters Both wetted perimeter and depth should expressed in feet Similarly a function of cross sectional area A in ft and depth in ft can be expressed as izor 28 where again o and o are numerical fitting parameters The top width T can be described as T y 29 It has been found that for most furrows the hydraulic section can be defined as NRCS National Engineering Handbook Part 652 National Irrigation Guide Template Chapter 9 Irrigation Water Management 64 p A 30 in which 10 4 31 10 3 pP 2 III 32 71 The values of and Cch are equal to the unit width used to describe the flow parameter p equals the unit width squared The values of o Cmh and for borders and basins are 0 0 1 0 0 0 and 3 33 respectively Values for furrows will be defined below Using the English form of the Manning equation the cross sectional flow area at the field inlet A in ft can be determined for any flow Q in cfs and field slope S greater than about 0 00001 as follows 2 21 m emo 1 33 5 P If the field has a slope less than 0 00001 then inlet area A will increase as the advance proceeds down the field and must be
20. LLI LE C a forthe aceon Wetted Perimeter m 0 0000 Figure 5 The Field Characteristics panel of the input tabbed notebook The geometry and topography of the surface irrigated field 15 described by inputting the following parameters Field length and width Field cross slope Type of system furrow or border basin Unit spacing for borders and basins or furrow spacing Downstream boundary condition Manning roughness n for the first and later irrigations Three slope values in the direction of flow Furrow spacing refers to the spacing between adjacent irrigated furrows When alternate furrows are irrigated an unused furrow lies between the irrigated furrows and 15 not considered in the definition of furrow spacing 26 Two distance parameters associated with the three slopes Four measurements of flow cross section II 4 1 1 Basic Field Geometry The basic geometry of the field includes its length or the distance water will run its width and cross slope the type of surface irrigation system a unit width or furrow spacing and the nature of the downstream field boundary The field s cross slope 1s not utilized the software but is needed to design the headland pipes or ditches used to irrigate the field These parameters are constant within each field and may not represent the entire area being irrigated The simulation program evaluates the hydraulics of the irrigation over a unit width
21. 0011076 0012486 0013810 0015069 0016254 0021291 0025134 0033454 amp To determine Kostiakov Lewis parameters for border and basin irrigation it has been assumed that the infiltration through the furrow perimeter 15 uniform and that the a exponent 15 the same for both situations Recognizing that one dimensional border basin infiltration will be different per unit width than in furrow a reference wetted perimeter for each furrow family has been defined that 1s intended to compensate for these differences Figure III 5 shows typical values of wetted perimeter for furrow irrigation in each of the soil families These values will change with slope roughness crop and cultural practice and are therefore only for reference purposes To convert from furrows to borders or basins the furrow coefficients are divided by the reference wetted perimeter Tables for initial and later border and basin irrigation under both continuous and surged flow are given in Tables III 7 to III 10 Reference Furrow Wetted Perimeter S un S un S Wetted Perimeter inches lt gt 0 00 0 50 1 00 1 50 2 00 2 50 3 00 3 50 4 00 NRCS Intake Family No Figure III 5 Reference wetted perimeters for the revised NRCS intake families It 1s also necessary to specify a reference discharg
22. N or Pipe Recycled Water Supply Reuse 77 NE AD ON Tailwater 2 Tailwater Channel Reservoir Figure IV 13 Schematic tailwater reuse system If the surface runoff 1s to be captured and utilized on another field the reservoir would collect the runoff from the n sets of Fig IV 13 and then supply the water to the headland facilities of the other field This requires a larger tailwater reservoir but perhaps eliminates the need for the pump back system In the simplest case of runoff reuse on an independent part of a field the design 1s same whether the tailwater 15 collected and reused on the originating field or on another field The procedure listed below deals with reuse on the originating field Compute inflow discharge per unit width per furrow and time of cutoff for a free draining system that achieves as high an irrigation efficiency as possible without recycling This discharge 1s a reasonable trade off between the losses to deep percolation and tailwater and therefore will tend to minimize the size of the tailwater reservoir Evaluate the subdivision of the field into sets that will accommodate the total available flow and the duration of the supply Compute the total runoff volume per unit width or per furrow from the originating field Compute the number of furrows or unit widths that can be irrigated from the recycled tailwater and the number that will be irrigated wit
23. One of the early systems 15 shown in Fig I 16 The complexity and cost of these systems proved to be infeasible and a simpler system involving an automated butterfly valve like the one shown in Fig I 17 was developed to implement surge flow by sequentially diverting the flow from one bank of furrows to another on either side of the value 9 igure I 16 Early surge flow system The automated butterfly valves have two main components a butterfly valve and a controller The valve body is an aluminum tee with a diverter plate that directs water to each side of the valve The controller uses a small electric motor to switch the diverter plate and its type varies with its manufacturer Most controllers can be adjusted to accomplish a wide variety of surge flow regimes For instance most controllers have both an advance stage and a cutback stage During the advance stage water is applied surges that do not coalesce and can be sequentially lengthened Specifically it is possible to expand each surge cycle so surges that wet the 20 downstream ends of the field are longer than those at the beginning of irrigation During the cutback stage the cycles are shortened so the individual surges coalesce Brass bushings j Actuator Diverted left O rings Butterfly flap Diverted right Figure I 17 The automated butterfly surge flow valve Adaptation for border and basin syst
24. Typically the unit width for border and basin simulation 15 one foot but can be other dimensions if desired Whatever value that is selected must be consistent with Simulated Unit Flow In other words 1f the unit width 1s 2 5 ft the simulated unit flow must be the discharge onto the border or basin that flows within this width If the system 1s configured for furrows the simulation evaluates the flow in a single average furrow II 4 1 2 Manning n One of the most important considerations in surface irrigation evaluation and design 15 the changes that occurs on the field surface as it is irrigated Newly tilled soil is usually hydraulically rougher than soil surfaces that have been smoothed by the flow of water during irrigation On the other hand surfaces such as borders and basins may become hydraulically rougher as crop density and size increase The SURFACE software includes the feature necessary to examine two field conditions which are noted as first irrigation and later irrigation conditions In order to perform the various simulations the software requires input of two estimates of the Manning n coefficient for these two conditions Freshly constructed furrows typically have values of about 0 03 0 05 depending on the soll aggregation Previously irrigated furrows without crops growing in the furrow itself will have substantially lower values Measurements have been reported where these values have been as low as 0
25. eie 28 42 Infiltration px ee ln tatu 29 B t E E M Cue 32 4 3 1 Simulation Shutoff CODITOL e 33 4 3 2 low REUNIE ete 33 4 3 3 Prae Hotte oc UE EE Eie EE E 34 4 3 4 Simulation Speed and Graphical Presentation sse 34 4 oa mE E E EE ME M CE 34 MAS 36 US ipee 36 Printed 36 SEEN VOUS E 36 SIMULA MON O 38 TET DESIGN Pec 39 deputata for 40 II 7 1 1 valable d Ree a a 40 ii II 7 1 2 Total Linie Pow r Avaa b E totae tute Doct 40 II 7 1 3 Maximum Velg e 41 7 1 4 41 7 1 5 41 W AVO uidi NEUE LEM 42 I3
26. 2 2 Gated Outlets There are several gates used in gated pipe They range from slide gates to simple plugs and the discharge characteristics depend on their size and shape A typical head discharge curve for fully open slide gates is shown in Fig IV 18 and is presented for general guidance In design practice it will be necessary to know the specific characteristics of the gate actually used in the pipe Figure IV 18 is intended to be an approximate tool that can be used to size the gated pipe itself 104 General Head Discharge Relation for Gated Pipe Outlets Gate Discharge gpm Seo SS 0 0 0 0 5 1 0 1 5 2 0 2 5 3 0 3 5 Head feet Figure IV 18 Typical head discharge curve for gated pipe outlets It should also be noted that preceding any design of the headland facilities the design of the field system must be completed so the unit flows and times of cutoff are known Then from Figure IV 18 the operating head on the fully open gate can be determined which corresponds to the design unit flow furrow flow This 15 the minimum design head in the gated pipe The flow from gates closer to the inlet end of the pipe will require regulation by adjusting the gate opening Finally gates should be spaced along the pipe at the same distance as the furrow spacing even when alternate furrows are irrigated IV 4 2 3 Gated Pipe Sizing The design of gated pipe relies on several pieces of information Fro
27. 35 Changing the Field Geometry and Topography Cultivation planting and harvesting with modern US agriculture and its advanced mechanization are more efficient for large fields with long lengths of run As the soil texture in a large field may range from clay and clay loam to silt loam and sandy loam the length of the field may be too long for efficient surface irrigation Dividing the field in half thirds or quarters is often an effective way to achieve better uniformities and efficiencies However because a field subdivision costs the farmer mechanization efficiency land area and money for the changes surface irrigation should be evaluated first using the field dimensions that correspond to property lines organization of supply pipes or ditches or what the farmer 1s currently doing Good design practice avoids slope changes unless necessary to change type of surface irrigation system Surface irrigation can be configured to work well within a range of slopes between 0 and 0 5 If a flatter slope is needed to control erosion at the end of a sloping field flattening the last quarter of a field s slope 1s easily accomplished with modern laser guided land leveling equipment and need not be prohibitively expensive surface irrigation performance can always be improved by accurate leveling and smoothing of the field surface As noted previously most irrigators consider precision land grading as the best water management practice Furrow
28. 4 2 4 Example Gated Pipe Design In the example give Section IV 3 1 FreeDrainingFurrow 1 Example the field was 1 180 feet long and 2 362 feet wide The field design for initial irrigations called for eighteen sets to be organized by subdividing the length into two parts and the width into nine parts see Fig IV 5 The cross slope was 0 0001 The design furrow flow was 22 5 gpm and the total flow 1s 2 362 gpm Suppose this field is to be irrigated by a gated pipe system supplied by a buried pipe mainline as shown in Figure IV 19 in which the basic supply enters the field in a 1 500 foot pipe from the upper left hand corner traverses to the middle of the field width then turns 90 and extends to the mid point of the field length The supply pipe connects to a canal offtake in which the water elevation is 15 feet higher than the 90 turn Optimally the pressure head at the 90 turn should be 6 feet eu Control Valve Inlet Valve SES BEB ee Buried Mainline Gated Pipe Run Length fi 531 Run Width 252 Figure IV 19 Layout of FreeDrainingFurrow 1 gated pipe system A conservative estimate of the friction loss in the supply pipe can be determined from Eq IV 11 by using the canal free surface as the reference point Thus _ 0 0 15 feet 6 LL 6 6 fi 100 ft 7 supply pipe 1500 100 mn 107 From Table IV 4 it can be seen that 2 400 gpm flow with a 0 06 ft 100t friction gradient can be conveyed w
29. INITIAL TABLE 4 CONTINUOUS FLOW FURROW INTAKE FAMILIES LATER IRRIGATIONS Heavy ID Soil Clay Clay Clay Light Clay Clay Clay Clay Loam Loam Loam Silty Silty Silty Silty Silty Silty Sandy Sandy Sandy Loam Loam Loam Loam Loam Loam Loam Sandy Sandy Sandy Heavy ID Soil Hame Clay Clay Clay Light Clay Clay Clay Clay Loam Loam Loam Silty Silty Silty Silty Silty Silty Sandy Sandy Sandy Loam Loam Loam Loam Loam Loam Loam Sandy Sandy Sandy D D D d ft 3 ft anan a ft 3 ft nman Dec ft J ft mn a ft 3 E t man IRRIGATIONS K 002420 004466 006823 008710 010346 011807 013140 014396 015563 016671 017740 019730 021591 023352 025004 026596 033670 039806 059571 K 002060 003786 005803 007410 008786 010037 011170 012236 013233 014181 015070 016770 018351 019842 021254 022606 028620 033846 050631 D D D D
30. IRRIGATION CONCEPTS III 2 1 Soil Moisture As commonly defined the available moisture for plant use 1s the soil water held in the soil matrix between a negative apparent pressure of one tenth to one third bar field capacity and a negative 15 bars permanent wilting point However the soil moisture content within this pressure range will vary from 3 inches per foot for some silty loams to as low as 0 75 inches per foot for some sandy soils Consider the simplified unit volume of soil comprised of solids soil particles liquid water gas air as shown in Fig 1 The porosity 9 of the unit volume 15 E III 1 9 V The volumetric water content 0 1s V III 2 7 2 The saturation S which 1s the portion of the pore space filled with water 1s S Vo III 3 Porosity saturation and moisture content soil are related by the expression So III 4 There are a number of ways to measure water in a soil These include tensiometers resistance blocks wetting front detectors soil dielectric sensors time domain reflectometry frequency domain reflectometry neutron moderation and heat dissipation However one of the Charlesworth P 2000 Soil Water Monitoring Irrigation Insights Number 1 Land and Water Australia GPO Box 2182 Canberra 2601 Australia 96 p Email lt public iwa gov au gt 46 most common and simplest 15 the gravimetric method in which soil samples are extr
31. See cutoff time The ratio of the volume of water to the volume of pore space in a soil Relatively short light weight curved tube used to divert water over ditch banks slide gate A regulated ditch or canal offtake used to divert water to irrigated borders and basins See also ditch gate soil dry weight The weight of a soil sample after being dried in an oven at 95 105 C for 12 24 hours Usual units are grams since as metric units are typically used for these measurements soil moisture content 0 The ratio of the volume of water in a soil to the total volume of the soll XIV soil moisture depletion SMD The depth or volume of water that has been depleted from the available water 1n a soil This can also be viewed as the amount of water required to return the soil moisture to field capacity specific gravity ratio of the unit weight of soil particles to the unit weight of water at 20 spile A small pipe or hose inserted through ditch banks to transfer water from an irrigation ditch to a field subbing The horizontal movement of water from a furrow into the row bed surface irrigation broad class of irrigation systems where water 1s distributed over the field surface by gravity flow See border basin and furrow irrigation surge irrigation surface irrigation by short pulses or surges of the inflow stream during the advance phase and then by high frequency pulses or surges during the wetting or ponding
32. The root zone deficit Zreg 1s entered in the input boxes below the Tables buttons These values are always entered as the target depth of irrigation or the depth of the soil Root one Moisture Depletion zreq inches 4 000 4 000 4 000 4 000 Hequired Intake Opportunity Time min moisture deficit can be converted to an equivalent volume per unit length as follows 204 302 737 536 259 928 415 533 7 Ww req 1 7 in which w is the unit width feet for borders and basin the irrigated furrow spacing For convenience the values of root zone moisture depletion in these input are entered in units of inches and then are converted into units of feet for use in the infiltration equations where fo and c values have units of ft ft min and ft respectively for borders and ft ft min ft ft min and for K F and in furrow infiltration Below the input boxes for the root zone depletion are the associated intake opportunity times to achieve infiltration equal to the root zone deficit In the figure above a 4 inch deficit 31 will require 204 minutes of infiltration These input boxes are updated whenever values of the intake coefficients or z 4 are input Values of intake opportunity time can also be input directly and the values of Zreg will be adjusted automatically At the bottom of the page are four checkboxes to switch between English and metric units and betw
33. an interactive design feature Both of these will be described separately below 3 1 File Operations and Exiting SURFACE The program and any window or screen Input Output Units Simulate Design object can be closed by clicking on the E buttons Open i The program itself can also be closed by clicking Save 5 the File menu selecting Exit as shown here Save As Existing input files can be accessed through ZZ EE the open menu item under the File drop down menu as shown or by clicking the speed button Once the user has finalized a set of input data it should be saved to an existing or new file Saving to an existing file can be accomplished from the File menu using the Save option or 23 by clicking on the save speed button ll Save As option from the File menu reveals a dialog box which the user can save the data under a new file name 3 2 Input Both the Input menu and the speed button input tabbed notebook to appear in the main screen and viewed 4 one click actions that will cause as shown in Fig II 3 Data can then be input Inflow Controls Field Topography Geometry Infiltration Characteristics Hydrograph Inputs Design Panel Field Geometry Field Length m 360 0 Field Width m 200 0 Field CrossSlope 0 00000 Border B asin Unit 1 00 Width m or How Spacing m Field System Border Basin Irrigation Furrow Irriga
34. and permanent wilting point become 47 0 yW 8 Wp 9 The total available water to the plants is approximately the difference in these volumetric moisture contents multiplied by the depth of the root zone RD TAW 0 0 RD 10 It should be noted that 10 1s not technically exact because crop roots do not extract water uniformly from the soil profile The relation among field capacity permanent wilting point total available water and soil type is illustrated in Figs III 2 and III 3 Table III 1 lists some common rooting depths for selected crops Saturation Gravitational Water rapid drainage Field MAD Capillary Water very slow drainage 222222 rmm mm rmm rmm rmm rmm mmm mm Permanent Wilting Point 222212272222 Hydroscopic Water essentially no drainage Oven Dry Figure 2 Components of soil water i Doorenbos J and W O Pruitt 1977 Crop Water Requirements Revised Edition FAO Irrig Drain Pap 24 United Nations Food and Agriculture Organization Rome 48 Permanent Wilting Point Volumetric Moisture Content ba Sandy Silt Clay Lean Loam Cle Loam Loam Soil Classification Figure III 3 Variation of available soil moisture with soil type TABLE III 1 AVERAGE ROOTING DEPTHS OF SELECTED CROPS IN DEEP WELL DRAINED SOILS Root Depth Ro
35. applying water to croplands Also referred to as flood irrigation the essential feature of this irrigation system 15 that water 15 applied at a specific location and allowed to flow freely over the field surface and thereby apply and distribute the necessary water to refill the crop root zone This can be contrasted to sprinkle or drip irrigation where water 15 distributed over the field pressurized pipes and then applied through sprinklers or drippers to the surface Surface irrigation has evolved into an extensive array of configurations which can broadly be classified as 1 basin irrigation 2 border irrigation 3 furrow irrigation and 4 wild flooding The distinction between the various classifications is often subjective For example a basin or border system may be furrowed Wild flooding 15 a catch all category for the situations where water is simply allowed to flow onto an area without any attempt to regulate the application or its uniformity And since no effort is made to regulate the application or uniformity this type of surface irrigation does not need attention in this handbook If control of the wild flooding event 15 introduced it then evolves into a border basin or furrow system An irrigated field 15 only one component of an irrigation system as illustrated in Fig I 1 CARSHALL DELIVERY SYSTEM WATER USE LL 2 SYSTEM DIVISION BOX TAIL WATER AIL WATER DITCH T WATER REMO
36. cases of variable cycle surge flow the cycle times can be compressed by specifying a value less than 1 0 for Surge Adj Ratio or a negative number for Surge Adj Time the user should be careful with this input The concepts of continuous and surge flow are fairly standard surface irrigation terms Cutback 1s a concept of having a high initial flow to complete the advance phase and a reduced flow thereafter Both continuous and surged systems can 1 00 operate with a cutback regime If a cutback regime 1s selected two additional parameters are required Length Fraction first 15 the definition of Cutback Ratio and the second is the definition of Length Fraction A cutback ratio of 0 80 results 1n a reduction of inflow to 80 of the initial flow A cutback length fraction of 0 8 initiates the cutback flow when the advance has completed 80 of the field length Likewise a cutback length fraction of 1 2 results in the cutback when the software estimates the advance would have exceeded the field length by 2096 In surge flow simulation the CB Length Fraction should always be set to a value greater than 1 0 There 15 one note of caution If the advance phase has been completed and the cutback 15 sufficient to dewater the end of the field the simulations will often fail These are situations where the cutback causes a front end recession prior to inflow shut off In some cases the simulations will compute the front e
37. concept of cutback has been around for a long time A relatively high flow is used at the start of an irrigation to speed the advance phase along and then a reduced flow 15 implemented to minimize tailwater As a practical matter however cutback systems have never been very successful They are rigid designs in the sense that they can only be applied to one field condition Thus for the condition they are designed for they are efficient but as the field conditions change between irrigations or from year to year they can be very inefficient and even ineffective One adaptation of the concept was the Cablegation system Another was the development and adaptation of surge flow Both have provided a flexible method of applying the cutback concept although the complexity of Cablegation is problematic The SURFACE software does allow one to simulate the conceptual cutback regime for both continuous and surge flow systems Cutback irrigation involves a high continuous flow until the advance phase 15 nearing completion or has been completed followed by a period of reduced or cutback inflow prior to the time of cutoff The concept of cutback 1s more applicable to furrow irrigation systems than border systems and will thus be illustrated herein 3 3 1 Example Furrow Cutback Design Run the SURFACE software with CutbackDesing cfg file loaded Notice that the data file in the input tabbed notebook indicates the inflow regime has been defined by c
38. dialog boxes Advance Recession Data Tailwater Data The Current Data Plot Options selection provides plots of advance and recession a runoff or tailwater hydrograph depth of Applied Death Date water at the end of the field and the distribution of applied depths Save Exit 36 over the field typical plot of the advance recession data is shown in Fig II 11 showing as well data from recorded field measurements Figure II 12 shows a typical tailwater hydrograph and Fig II 13 shows the plot of infiltrated water Tene Hours 169 100 408 100 1020 1100 1200 ntu feu alona Field fect Figure 11 A typical advance recession plot from the SURFA CE graphics output File Current Plot Options rs 030 Wlapeerd Time Figure 12 A typical runoff hydrograph from the SURFACE graphic output 37 Distance along Field feet 100 200 300 400 500 600 700 800 900 1000 1100 1200 4 0 Figure II 13 A typical plot of intake distribution for the SURFACE graphics output 6 SIMULATION Once the input and control data have been entered the simulation 1s executed by clicking on the calculator button or the simulate menu The simulation screen will appear and the run time plot of the advance and recession profiles will be shown as illustrated in Fig II 14 inp Hedus v
39. field must be irrigated at different times II 7 1 3 Maximum Velocity In order to prevent erosion the designer will need to place an upper limit on flow velocity over the field This limit may be as low as 30 ft mn for erosive soils to as high as 75 ft mn if the soil 1s quite stable The actual velocity over the field will be highest at the field inlet and will depend on the unit discharge field slope and field roughness Generally erosive velocity is more of a concern in furrow irrigation than in border irrigation It 15 generally not a concern in basin irrigation except near the delivery outlets Typical values of maximum velocity for furrow systems are shown in the following table Suggested Maximum Soil Type Non Erosive Velocity in feet min sandy Loams Clay Loams II 7 1 4 Design Flow The performance of surface irrigation systems 1s highly dependent on the unit discharge and thus this parameter may be the most important management parameter either the designer or irrigator considers Unit flows that are too small advance slowly and can result in poor uniformity and efficiency as well as excessive deep percolation Flows that are too high may result in low efficiencies due to excessive tailwater or downstream ponding although the uniformities will typically be high In an interactive design process the designer searches for a design flow that maximizes efficiency subject to a lower limit on adequacy For example one may wi
40. from the cropped surface plant and soil Usual units are inches contour irrigation The practice of arranging furrows borders or basins along the natural contours of a field conveyance efficiency see irrigation efficiency conveyance loss cropping pattern crop root zone Water lost from the conveyance system due to evaporation seepage from the conveyance ditch pipe canal etc leakage through control and turnout structures or valves or 15 unaccounted for due to measurement errors The term cropping pattern has two connotations The first 1s the seasonal sequence of crops grown on a single field The second is a more general term describing the distribution of cropped acreages in an area in any one year The soil depth from which crop extracts the water needed for its growth This depth depends on the crop variety growth stage and soil Usual units are inches or feet cumulative intake z Z The depth 2 or volume per unit length 2 of water infiltrating a cutback irrigation cutoff time tco cycle time deep percolation DP deficit irrigation depletion time tq distribution system ditch ditch gate field during a specified period usually the time between the initiation of irrigation and the end of the recession phase Usual units are feet or inches for z and cubic feet per foot of length for furrows The practice of using a high unit discharge during the advance phase and a reduced one d
41. have less impact on efficiency and uniformity than they do in either basin or border irrigation arde URS PRA gt RAG 22 4 4 a COE ee Figure 1 5 Contour furrow irrigation 1 2 2 3 Soil Characteristics Furrow irrigation can be practiced on nearly all soils but there are two important limitations First the risk of erosion is higher in furrow irrigation than in either basin or border irrigation because the flow is channeled and the flow velocities are greater Secondly since the furrow actually wets as little as 20 of the field surface depending on furrow spacing applying relatively large depths of irrigation water in the heavy soils can require extended periods of time and will result in low efficiencies A four or six inch irrigation application is common basin and border irrigation but would not be feasible with a furrow system on a particularly heavy soil Furrow irrigation is more impacted by soil cracks than borders and basins since the cracks often convey flow across furrows Furrows are probably less impacted by restrictive layers due to their inherent two dimensional wetting patterns 1 2 2 4 Water Supply Since the flow on the field 15 substantially less than a basin or border system a major advantage of furrow irrigation 1s that it can accommodate relatively small delivery discharges per unit area As furrows typically apply smaller depths per ir
42. important are the distance from the inlet to the field midpoint and to the end of the field Doing so but consolidating known terms on the right hand side yields the following two volume balance expressions 1 t 6 4 boy c I 55 1 Qt s 51 7 1 F t 151 c Kt 1 1 56 Taking the log of both equations provides a definition of a as follows in y 11 57 log 72 Then 15 computed from 37 in order to find from Eq 50 Then 15 found by substitution back into Eq III 55 I III 58 o t 2 Select 10 20 points along the field length including the inlet and field end and compute the depth of infiltration at each point using Eq III 15 the Kostiakov Lewis equation with the a K and F parameters available from Step 1 along with the intake opportunity time from Eq 48 Then determine the total volume of infiltrated water as demonstrated in subsection III 2 3 7 3 The total volume of infiltration computed in Step 2 should equal the volumetric difference between the inflow and outflow hydrographs for free draining systems or the total inflow for blocked end systems This 15 unlikely for the first iteration unless the value of F is indeed the assumed value Generally the volume of infiltration calculated in the first iteration will be too low F will need
43. in feet 100 feet L E Linet hy Equation IV 10 can be solved for hy as follows 7 EL 7 EL ie 7 H 11 h inte f L 100 Then with a computed value of hy the designer can select the proper pipe diameter from Table IV 4 TABLE IV 4 MINIMUM RECOMMENDED GATED PIPE DIAMETERS FOR VARIOUS FRICTION GRADIENTS Flow zpm Head Loss 700 800 1800 2800 3000 3200 3400 ft 100 ft Z 008 _ 7 S S SS YX gt QW QM WW 2 SAN Gnd C a che D EE m 2n ep e 22 inch E pb zu 2 5 i 2 55 TR HHH ie 2 5 5 i 5 gt L 15 in i ine hte 55 P 2 lt rhe choke chsh ht hb TRIER Ll
44. intervals than furrows or borders by applying a larger depth during irrigation Consequently medium to heavy soils with their high moisture holding capacity are better suited to basins than lighter soils The efficiency and uniformity of basin irrigation depend on the relative magnitude of the field inflow and the soil intake A soil with a relatively high intake characteristic will require a substantially higher flow rate to achieve the same uniformity and efficiency as for a heavier soil since the water may cover the entire basin surface a soil that forms dense crusts upon drying may have detrimental impacts on seed germination and emergence It is common practice to furrow soils of this nature to reduce crusting problems On the other hand basin irrigation 1s an effective means for reclamation and salt leaching Many of the heavier soils will form cracks between irrigations which may be responsible for much of the water that infiltrates during irrigation These soils are also susceptible to forming compacted layers hard pans or plow pans at the cultivation depth The impact of cracking basin irrigation is an increased applied depth while the impact of a plow is to restrict it 1 2 1 4 Water Supply The water supply to an irrigated field has four important characteristics 1 its quality 2 its flow rate 3 its duration and 4 its frequency of delivery The quality of the water added to the field will be reflected i
45. midpoint 3 the time of advance 4 the time of cutoff 5 the time of recession at the field inlet 6 the recession time at the field midpoint and 7 the time of recession Time of Recession Time Cutoff af Advance Time since Irrigation Started A Distance from Field Inlet L Figure III 10 Field measurement points for advance and recession evaluations in the field As a practical matter the start time time of advance and recession time are all available from the inflow and outflow hydrographs if the field is free draining Blocked end fields will require the recession time to be noted when the ponded water vanishes 66 Two simple equations of advance and recession be developed For the advance trajectory a simple power relationship 1s usually sufficient x pt III 41 in which log pou 42 log 5 and p 2 III 43 t where x the distance from the field inlet to the advancing front ft t time from the beginning of irrigation until the advancing front reaches the point x min 51 the time from the beginning of irrigation until the advancing front reaches the field mid point min t the advance time min L the field length ft and r fitting coefficients The recession trajectory can be represented by a quadratic function t h i x j x 44 in which h t III 45 242 pu pw 2 m t t t m 1 OL E where m
46. moisture content 0 and can be expressed as a depth of water as follows SMD 0 0 RD 11 2 1 1 Example 1 of the most important characteristics of soil is its bulk density or bulk specific weight When evaluating soil moisture particularly with the gravimetric method this parameter 15 necessary to accurately estimate SMD MAD etc The following example 15 given to demonstrate these relationships What is the bulk density or bulk specific weight of an undisturbed sample 12 inches long by I inch in diameter and weighing when collected 0 573 lbs The entire sample was oven dried to specification and then saturated with 3 594 cubic inches of water The specific weight of the soil particles is 165 434 lbs ft The solution to this question 15 found Eq III 7 which relates porosity to bulk density and the specific weight of the soil particles Recognizing that the 3 594 in of water occupies the entire pore space in the sample then the porosity from Eq 1 is V Qm hu S 103812 38 156 V 1 4 Then from Eq 7 for yields y 1 9 165 434105 1 0 381 102 404 I5 1 649 2 p ft X cm III 2 1 2 Example 2 The most important uses of soil moisture characterizations are those that assist the irrigator determine when to irrigate and how much to apply A corollary problem for the surface irrigation evaluation 15 determining the soil moisture prior to irrigation so an estimat
47. of leaching is therefore 0 4 inches 990 ft 2 5 ft 12 82 5 The irrigation efficiency from Eq 20 1s 1125 82 5 2502 0 483 or 48 3 III 2 4 Water Measurement One of the simplest and yet most important concepts in surface irrigation can be described mathematically as follows DA 1 26 where Total flow delivered to the field Total time the flow 1s delivered to the field D Depth of water applied to the field A Area of the field As an example if it requires a flow of 10 cfs for 48 hours to irrigate a field of 40 acres the depth that will be applied will be about 12 inches The flow rate delivered to a field is critically important in two respects First the surface irrigation system is highly sensitive to the flow because it determines how fast or slow the field will be irrigated And secondly the efficient surface irrigator must judge the effectiveness of his management by planning a target depth of application for each irrigation and then assessing the performance of the system as it operates In both cases a significant difference between the flow necessary to apply the appropriate depth in the planned period and the actual flow delivered will adversely impact the 63 efficiency and uniformity of the surface irrigation Flow measurement is vitally important in surface irrigation The NRCS uses the Water Measurement Manual of the Bureau of Reclamation U S Department
48. on cropped surface for an extended period of time the oxygen carbon dioxide exchange between the atmosphere and the roots 1s disrupted If the disruption 15 long enough the crops will die This process 15 sometimes called scalding Scalding is perceived as a serious risk in basin irrigation by irrigators in hot dry climates Of course rice farming depends on this process for weed control Another climate related impact of basin irrigation 1s the effect of water temperature on the crop at different stages of growth Irrigation with cold water early in the spring can delay growth whereas the hot periods of the summer it can cool the environment both of which can be beneficial or detrimental in some cases One important advantage of basins in many areas of high rainfall is that they can more effectively capture it than can borders or furrows Thus basins enjoy the benefits of higher levels of effective precipitation and may actually require less irrigation delivery during rainy periods as long as the crops are not damaged by subsequent scalding or flooding 1 2 1 6 Cropping Patterns With its full wetting and large applied depths basin irrigation 1s most conducive to the irrigation of full stand crops like alfalfa grains grass and rice Row crops can be and often are grown in basins as well Widely spaced crops like fruit trees do not require as much of the total field soil volume to be wetted and thus basin irrigation in these in
49. printout of the software s basic input data then the Print Input Data option can be selected 5 1 Printed Output Figure II 4 showed the primary printed output screen Selecting the File 52 Sule option from the main command bar provides nad Existing Output File Save Output File Print Adv Rec Intake Data Print End Depth Runoff Data Units Simulate Design various print and save options Data can be saved in a comma delimited text file but the mini spreadsheets on the form are also Save AdviRec Intake Data to Comma Delimited Text File Microsoft Excel compatible so the user can Save End Depth Runoff to Comma Delimited Text File also drag and drop or copy and paste the data f Ext from the screen directly Tabular output can be either printed or previewed Each selection of the print or save options allows the user to choose one of two sets of data 1 the advance recession infiltration profiles and or 2 the runoff hydrographs A Units option on the main command bar is available to change the units of previewed or printed data 11 5 2 Plotted Output Current Data Plot Options Choosing plotted output reveals the plotting screen The pen Existing Output File screen command bar has two drop down menus accessed by selecting Files or Current Data Plot Options The Files options are either to open and existing output file or to save the current output to a file either of which lead to standard file open save 3
50. puede ML 22 V az z W L 2 3 4 Distribution Uniformity Application or distribution uniformity concerns the distribution of water over the actual field and can be defined as the infiltrated depth or volume the least irrigated 25 of the field divided by the infiltrated depth or volume over the whole field 61 DU 23 2 3 5 Deep Percolation Ratio The deep percolation ratio indicates the fraction of applied irrigation water infiltrating the soil that percolates below the root zone V V DPR 2 24 2 3 6 Tailwater Ratio The tailwater ratio 1s the fraction of irrigation water applied to the field that runs off as tailwater TWR aa ae III 25 2 3 7 Example A furrow irrigated set consists of 27 furrows spaced 30 in apart with a furrow length of 1320 ft At the time that the irrigation event was begun the soil moisture deficit was 4 3 in The estimated leaching requirement was 0 4 inches Each furrow had an inflow of 13 gpm for 24 hours The distribution of infiltrated water depth along the furrow length was as follows Furrow Infiltrated ment CONAMA What were the values of the various efficiencies and uniformities for this irrigation event In most field evaluations the volume of tailwater will be measured The exception of course 1s for the case of basins or blocked end borders where runoff is restricted In this case the volume of tailwater 1s not given
51. rate of a ponded soil surface Usual units are cubic feet per foot of length per minute for furrows and feet per minute for borders and basins Irrigation by flooding level fields The perimeter of basins is usually fully contained by surrounding dikes The practice of using dikes at the downstream end of the surface irrigated field to prevent or control runoff tailwater A surface irrigation configuration in which irrigation is applied to rectangular strips of the field Borders typically have a slope in the direction of irrigation but not laterally Mass of dry soil per unit volume Typical values in irrigated soils range from about 65 pounds per cubic foot Ibs ft 1 05 g cm for a clay soil to as much as 100 15 1 6 g cm for sandy soils An automated surface irrigation system employing a continuously moving plug in sloping gated pipe Outlet flows are highest near the plug and diminish away from it thereby creating a cutback regime Abbreviation for cubic feet per second a common English unit of discharge which is a rate of the flow or discharge equal to 448 8 gallons of water flowing each minute gpm or 28 32 liters per second lps The process of applying chemicals to an irrigated field through irrigation stream Chemigation is also referred to as fertigation when used to define through system fertilizer applications The water extracted by plants from the soil during their growth process or evaporated
52. re computed for each advance distance For this case the value of the field slope 5 1s replaced in Eq 33 by 11 34 x where y 1s the depth of flow ft at the field inlet and x 1s the advance distance in ft Figure III 8 illustrates the basic border basin and furrow shapes Measuring a furrow cross section in the field involves four simple measurements 1 the total depth of the furrow Ymax 2 the base width Base 3 the top width at the Ymax depth Tmax and furrow width at depth of Y4 2 The units of and are feet The values of the furrow geometry and then be calculated as follows 8 For convenience the units used in the input boxes of the SURFACE software are inches The values of 4 02 P1 depend on the units used In the SURFACE software only the metric values are displayed 65 Ymax Furrows Y max Imax Tmid Base 1 0 Figure 8 Cross sectional shapes for furrow and border basin irrigation 022 72 log 35 36 2 7 11 37 A 52 38 66 zi T Cmh 39 log 2 ss 40 Cmh max 3 1 2 Rather than demonstrate these computations in laborious example the reader should open an application of the SURFACE software From the main screen click on the input data button i t
53. recession curve is defined by Eqs III 44 to III 47 h t 1444 min m t t t m 1 o where 7 LL 1015 0 494 L m m L 2050 5 494 1502 1482 1444 494 1 jM 0 04652 2050 5 494 494 pne cp III 3 2 Infiltration Not only 15 infiltration one of the most crucial hydraulic parameters affecting surface irrigation but unfortunately it 1s also one of the most difficult parameters to assess accurately 70 the field The importance of knowing the infiltration function in order to describe the hydraulics of a surface irrigation event along with the inherent difficulties 1n obtaining reliable estimates of this parameter means that the investigator should expect to spend considerable time and effort in assessing infiltration before proceeding with the design of a surface irrigation EF u E system E Se sn In the past the three most commonly employed techniques for measuring infiltration were cylinder infiltrometers ponding and inflow outflow field measurements For furrow irrigation the blocked furrow method has been used while a more recent technique 1s the flowing or recycling furrow infiltrometer III 3 2 1 Volume Balance Equation An alternative to making individual point measurements of infiltration 15 to compute a representative intake from advance recession and the tailwater hydrograph if available This involves a two l
54. the timing of irrigations in these areas is a critical issue If irrigation is completed immediately prior to a large rainfall event water may pond at the lower end and therefore the scalding potential might be substantial 1 2 3 6 Cropping Patterns Borders are used to irrigate most solid planting crops and if furrowed many row crops as well Widely spaced trees are usually not irrigated with borders unless the borders enclose the tree line and leave an empty space between tree rows And rice is not grown in borders Since the water ponds the entire surface crops with sensitivity to scalding may not be well irrigated with borders Likewise borders are better suited to deeply rooted crops like alfalfa than shallow rooted crops like vegetables 1 2 3 7 Cultural Factors Many growers like two things about borders the long travel lengths for their machinery operations and the slope to facilitate the application of water during the initial wetting These advantages are offset by more labor and management than for basins Properly designed and managed blocked end borders will have the same high efficiencies and uniformities as basins Leaching 15 better in borders than in furrows but not as good as in basins 1 2 1 8 Land Leveling Precision land leveling 15 just as important to high performance in border irrigation as it is for either basins where the ponding can compensate for some micro topography or furrows where the channeled flow wil
55. to be judged properly In fact furrow system cutoff times are usually after the completion of advance and for borders they are typically shorter and before the completion of the advance phase Consequently achieving high efficiencies 15 more difficult in border irrigation than in furrow irrigation Traditionally free draining borders have about the same efficiency and uniformity as furrows thereby reducing the economic feasibility of borders that allow tailwater However borders can also be blocked to prevent runoff and achieve efficiencies as high as those for basins thereby becoming slightly more economical than basins 1 2 3 2 Field Geometry Borders are usually long and rectangular in shape Often referred to as border strips borders contain the flow within side dikes to direct the flow over the field Borders can be furrowed where necessary for elevating a seed bed or compensating for micro topography within the border Borders can also be level or nearly level making them effectively the same as basins Distinguishing borders from basins 1s often based on the rectangular shape rather than slope and in any event the differences are only semantic 1 2 3 3 Soil Characteristics Borders do not generally have erosion problems except near outlets and tailwater drains so they are somewhat more flexible irrigation systems than furrows The slope aids advance and recession so border irrigation can be applied to the full range of soils so long a
56. value of f F are basic or long tern intake rates and may be set to zero for short irrigation events which are typical for borders and basins but generally not so for furrows The k or K and a parameters should always be defined Continuous Flow Intake Curve Parameterz for Initial Irrigationz ID 5011 Heavy Light Clay Clay Clay Silty Silty Silty Silty Sandy Sandy Sandy Clay Clay Clay Clay Loam Loam Loam Silty Silty Loam Loam Loam Loam Loam Loam Loam Sandy Sandy Sandy D ft 3 ft nan a ft 3 ft nman 002420 004466 006823 008710 010346 011802 013140 014396 015563 0166271 017740 019730 021591 023352 025004 026596 033620 039805 059571 Fo 0000786 0001981 0003369 00042704 0005974 0007212 0008396 0009548 0010656 0011733 0012777 0014768 0016652 0018417 0020096 0021629 0028384 0033508 0044606 ft Figure 8 The NRCS reference intake family for initial continuous flow furrow irrigations
57. 0014166 0015127 0015921 0016567 0017099 0017543 0018826 0019201 0017793 TABLE 10 SURGE FLOW BORDER BASIN INTAKE FAMILIES LATER IRRIGATIONS Surge Flow Intake Curve Parameterz for Later Irrigations fo ft an 0001624 0003722 0005599 0007064 0008245 0009218 0010065 0010793 0011425 0011989 0012496 0013349 0014044 0014608 0015084 0015473 0016609 0016945 0015692 59 2 3 Irrigation Efficiency Uniformity The effectiveness of irrigation can be described by its efficiency and uniformity Because an irrigation system applies water for evapotranspiration and leaching needs as well as occasionally seed bed preparation germination or cooling there have emerged a number of different efficiencies and ratios to give specific measures of performance The most important indicator of how well the irrigation served its purposes 15 how it impacted production and profitability on the farm When field with a uniform slope soil and crop receives steady flow at its upper end water front will advance at a monotonically decreasing rate until it reaches the end of the field If it 15 not diked runoff will occur for a time before recession starts following cutoff Figure III 7 shows the distribution of applied water along the field length stemming from these assumptions differences in applied depths are non uniformly distributed with characteri
58. 015 In the absence of more detailed information it is probably sufficient to use an value of 0 04 for first irrigations and 0 02 for later irrigations but the user has an opportunity to apply judgment here where necessary The Manning values for borders and basins vary over much wider range than they do for furrows primarily because they are affected by the crop and the geometry of its crown A freshly tilled and prepared border or basin with a bare soil surface probably has an value about the same as for furrows 0 03 0 05 After initial irrigations and before substantial crop growth the n value may be as low as 0 15 0 02 but later as the water is impeded by the crop values can be as high as 0 80 for a crop like an alfalfa grass mix The SURFACE software can be used in conjunction with field measurements of advance and recession to estimate the values and this will be described later II 4 1 3 Field Slope The SURFACE software 1s capable of simulating fields with a compound slope as shown in Fig 6 Up to three slopes can be located in the field by two distance values When the field 27 has only one slope the same value needs to be entered for all three slopes and both distance values should be set to the field length A field with two slopes can be defined by setting the second and thirds slopes to the same value and the second distance to be the difference between the field length and the first distance
59. 0462 constant in Eq A 9 by 0 7 to a new value of 0 7462 The basis of this adjustment 1s described in Chapter 5 Second Edition Furrow Irrigation Section 15 Irrigation or the National Engineering Handbook page 5 30 as account for both vertical intake which 15 influenced by gravitational forces horizontal intake which 1s influenced by suction forces the wetted perimeter 1s increased by an empirical constant of 0 700 This factor 1s an average value derived from studies that indicate that horizontal intake 1s a function of the 0 4 power of intake opportunity time A 4 MODIFICATIONS FOR BORDER BASIN AND FURROW IRRIGATION A 4 1 NRCS Intake Family Designation The basic infiltration rate generally occurs substantially beyond the time when that rate when the change of the rate per hour was one tenth of its value in inches per hour A more rationale and understandable concept for an intake family would be the average 6 hour intake rate A plot of the 6 hour intake rate for each of the previous NRCS intake curves is shown in Figure 1 Given the ambiguity of the definition of basic intake and the problems associated with this definition in the Kostiakov intake equations 1t seems reasonable to modify the concept of the intake family to one based on the average 6 hour intake rate in inches hour Furthermore the ring data originally used to develop the intake families have two very serious limitations First they
60. 1 Border and Basin Facilities and 2 2 2 6100000000000000000004 15 1 3 5 2 Furrow Irrigation Facilities and Automation 20 2 0 00000000000000000000000000 16 I 3 6 up M He 18 Lx IEEIBAHOD cueste M MM LS LT 2 IUE 19 I 3 7 1 Effects oF Surgme on Infilt altOn Is etam A ee ee 20 Lx52 FION OY SUIS idi 20 SURFACE NRCS SURFACE IRRIGATION SIMULATION EVALUATION AND DESIGN SORT WAR BD 22 22 IL2 GETTING STAR 22 Pile Operations and Pxatine SURFACE iecit piis isi Eel 23 E 24 DD OUPO sed en ios asad cash 24 jin EN TE 24 ISo EM 25 IEO 25 ENPU TL accidere ro 25 Entering Field Chatactetiste Sc Oa aes e E 26 4 1 1 ee 27 4 1 2 Mani iio IP C ted 27 4 1 3 ee 24 4 1 4 DIOS M
61. 2 cfg data set Following the procedure outlined above the first step 15 to determine a flow and cutoff time that achieves as high of uniformity and efficiency as possible One of the better options is to simply reduce the inflow from 0 033 cfs per furrow to 0 023 cfs per furrow and leave the cutoff time and target depth as defined This will reduce the tailwater fraction from about 40 to about 20 The volume balance within each furrow 15 Volume Balance in Cubic Feet computed in the performance box in the lower Outflow Infilt Error right hand side of the screen From the design 49874 398 0 4584 8 0 23 panel it can be observed that field during this initial irrigation would need to be divided into three sets Since the field is 2400 feet wide and the furrow spacing is 2 5 feet the tailwater from the first set and the size of the tailwater reservoir would be 2400 feet wide 1 398 fe furrow 2 5 feet furrow 3 sets 43 560 ft 2 92 ac ft From Eq IV 6 the number of furrows that can be irrigated by reuse 15 95 398 fr furrow 2400 ft _ 2 5 ft furrow gt 160 398 ft furrow 023 cfs 60 1440 mn The width of the field that should be irrigated by the main water supply 15 2400 160 x 2 5 2000 feet The value of 2 400 feet in the Field Topography Geometry input panel needs to be replaced by 2 000 feet to reconfigure the field width is
62. 3 85 5 1 0 0 000 0 2000 1394 3 92 7 TH 0 0 000 0 2000 1476 4 101 1 1 0 0 000 0 2000 1558 4 110 3 746 0 0 000 0 000 1640 4 118 7 1 0 J 000 000 1722 4 131 3 7515 Update Inflow Hydrograph Update Outflow Hydrograph Update Advance Recession Data Figure 10 Hydrograph Input panel of the input tabbed notebook The first mini spreadsheet describes the inflow hydrograph These data can be measured in the field or simply input by the user to test a flow change behavior of the system The hydrograph is defined by elapsed time the time since the beginning of irrigation and the discharge into a furrow or border basin unit width It 15 not necessary to develop and input these data on equal time steps as the software includes interpolation algorithms to match computational points with the input points The second hydrograph is for any surface runoff of tailwater that might be recorded or estimated It is not necessary to have tailwater hydrograph if for example the end of the field is blocked Finally a mini spreadsheet 15 available to record advance and recession trajectories In this case the data do not represent a hydrograph and may have points on the two trajectories where data are not available If data are not available for both trajectories or at certain points the user should enter a 1 as shown The software will ignore the negative values and use what data points are available to plot the trajectories B
63. 74 023266 029460 034836 0000667 0001679 0002863 0003993 0005081 0006125 0007136 0008116 0009052 0009967 0010861 0012551 0014155 0015661 0017082 0018428 0024133 0028481 ee EE EE EE EE M 052121 0037921 Sandy TABLE 6 SURGE FLOW FURROW INTAKE FAMILIES LATER IRRIGATIONS Surge Flow Intake Curve Parameters for Later Irrigations ID Soil Hame a K Fo Or Wpr a ft 3 ftz man gpm ft Heavy Clay Clay Clay Light Clay Clay Clay Clay Loam Loam Loam Silty Silty Silty Silty Silty Silty Sandy Sandy Sandy Loam Loam Loam Loam Loam Loam Loam Sandy Sandy Sandy D D 001940 003566 005463 006980 008276 009447 010520 011516 012443 013341 014190 015780 017281 018682 020004 021276 026940 031856 047651 0000592 0001485 0002530 0003531 0004489 0005403 000629 0007158 0007987 0008794 0009580
64. 80 54 14 129 95 239 na 98 2 4153 40 2 89 7 85 22 9 40 2 59 6 3 41 4 80 3 93 6 38 17 5 30 6 42 6 3 wm 212 307 3 ll d LI S 0 1766 1 A 5 and A 0 01282 x I 0 00175 B z0 A 6 Values of 5 and A were then computed for J values corresponding to the SCS now NRCS Intake Family designation 0 05 in hr to 4 in hr Rather than use these values as the basis for the intake families it was decided to convert Eq A 4 to the form of Eq 19 2 7 This was accomplished by using Eqs A 4 A 6 to compute values of for three values of 2 1 3 and 9 inches Then values of a and c were computed from the three points and became the NRCS Intake Family values in use until the publication of this chapter A 3 MODIFICATIONS FOR FURROW IRRIGATION Throughout the 1950 s and 1960 s a small group of SCS personnel also wrestled with the question of how to represent infiltration in furrow irrigation Field data were sparse but there were data which suggested that intake could be related to flow slope and roughness in other words wetted perimeter There was also some understanding that infiltration from the furrow sides was occurring at different rates than from the furrow bottom The methodology for developing intake relationships from advance recession and inflow outflow was not well understood Neverthel
65. Curve No 0 02 0 05 0 10 0 15 0 20 0 25 0 30 0 35 0 40 0 45 0 50 0 60 0 70 0 80 0 90 1 00 1 50 2 00 4 00 25 Initial Continuous Soil Type Flow Irrig 6 hour Intake Rate in hr Heavy Clay 0 022 Clay 0 055 Clay 0 099 Light Clay 0 145 Clay Loam 0 193 Clay Loam 0 242 Clay Loam 0 292 silty 0 343 Silty 0 395 Silty Loam 0 447 Silty Loam 0 500 Silty Loam 0 605 Silty Loam 0 710 Sandy Loam 0 815 Sandy Loam 0 918 Sandy Loam 1 021 Sandy 1 517 sandy 1 994 Sandy 3 966 Later Continuous Flow Irrig 6 hour Intake Rate in hr 0 017 0 042 0 074 0 106 0 138 0 170 0 202 0 234 0 265 0 296 0 326 0 386 0 445 0 501 0 556 0 610 0 855 1 074 1 834 Initial Surge Flow Irrig 6 hour Intake Rate in hr 0 018 0 045 0 080 0 115 0 150 0 185 0 221 0 256 0 291 0 326 0 361 0 429 0 495 0 560 0 624 0 686 0 973 1 234 2 180 e Reference NRCS Itake Family e Cumulative Intake inches NRCS Intake Family Later Surge Flow Irrig 6 hour Intake Rate in hr 0 016 0 039 0 068 0 097 0 126 0 155 0 183 0 211 0 239 0 266 0 293 0 345 0 396 0 445 0 492 0 538 0 745 0 926 1 527 06 Initial Cont Flow Later Cont Flow A Initial Surge Flow EF Later Surge Flow Figure 4 Average 6 hour intake rate for the revised NRCS furrow intake families 54 TABLE III 3 CONTINUOUS FLOW FURROW INTAKE FAMILIES
66. FACE EXE file and several sample input data files with a cfg extension SPECIAL CONTROLS The opening or main screen of SURFACE 1s shown above as Fig II 1 Program controls can be accessed via either a set of speed buttons or a series of drop down menus A closer look at this part of the main screen 15 shown in Fig II 2 22 deu Cg Une Besguu smutM SURFACE Surface Irrigation Evaluation Design and Simulation United States Department of Agriculture National Water and Climate Center Figure II 1 The main SURFACE screen File Input Output Units Simulate Design E35 S Bue erm Figure II 2 The SURFACE command bar The SURFACE software can be run from the Run command of the Windows Start menu by double clicking on NRCS SURFACE EXE from the Windows Explorer by clicking a shortcut icon the user has created In whatever case the first program screen the user sees will be as shown above will involve four basic tasks 1 inputting or retrieving data from a file 2 manipulating data and storing them 3 simulating the surface irrigation system described by the input data and 4 viewing storing and printing results In addition there are two special cases provided the software to manipulate data and or simulations The first 1s to derive infiltration parameter values from field measurements and the second is to simulate alternative system configurations as part of
67. Field Surface Slope Field Length Distance From Field Figure II 6 Illustration of multiple sloped surface irrigated field II 4 1 4 Flow Cross Section The flow cross section is defined and computed with Borgers and Basins four parameters top width middle width base and maximum depth these are entered eight parameters labeled Rhol Rho2 Sigmal Sigma2 Gammal Gamma2 Cch and Cmh are automatically computed It is important that the four dimensions required in the input screen are those that are associated with the unit discharge for border and basins or per furrow for those systems If the Field System selected 15 a border or basin the values of top width middle width and bottom width are the same and equal to the unit width The values of Rhol pj Rho2 Sigmal Sigma2 62 Gammal yj Gamma2 2 Cch and Cmh are based on the following relationships lt Tmax Tmid Base Unit Width WP AR p A _ 10 4 P2 73 10 3 5 71 T Cch yo 6 28 The parameters WP A R and T are the flow cross sectional wetted perimeter cross sectional area depth hydraulic radius and surface top width respectively For borders and basins in which the unit width is b feet the values of the respective parameters are y2 0 1 6 o2 1 p2 10 3 b and Cmh 0 For furrows these parameters take
68. Figure I 3 illustrates the most common basin irrigation concept Figure I 3 Typical basin irrigation system in the western U S 1 2 1 1 Development Costs Basin irrigation is generally the most expensive surface irrigation configuration to develop and maintain but often the least expensive to operate and manage Land leveling 15 most costly development and maintenance requirement although the perimeter diking can also be expensive to form and maintain In areas where turnouts from the delivery system have relatively small discharges development costs may also be increased by necessary changes in the irrigation system upstream of the basin Since basins are typically designed to pond the water on their surfaces and prevent tailwater they are usually the most efficient surface irrigation configurations addition management is almost always simpler 1 2 1 2 Field Geometry In the absence of field slope to aid the movement of water on the field surface the length or distance the water has to advance over the field tends to be minimized Many basins take a square rather than a rectangular shape but this depends entirely on the availability of sufficient flow rates and the intake characteristics of the soil One of the major advantages of basins 15 their utility in irrigating fields with irregular shapes and small fields 1 2 1 3 Soil Characteristics Basin irrigation systems usually operate at less frequent
69. H GATE SIZES FOR SURFACE IRRIGATION SYSTEMS 525 aedes oe desee 103 TABLE IV 3 MINIMUM RECOMMENDED CHECK OUTLET AND LARGE DITCH GATE SIZES FOR SURFACE IRRIGATION SYSTEMS 103 TABLE IV 4 MINIMUM RECOMMENDED GATED PIPE DIAMETERS FOR VARIOUS FRICTION GRADIENTS 106 TABLE A 1 LAYERED SCS RING INFILTROMETER 112 GLOSSARY ac ft advance phase advance time common English unit for water volume called an acre foot It is the volume of water required to cover an acre with water one foot deep One ac ft equals 325 851 gallons or 1 233 cubic meters The period of time between the introduction of water to surface irrigated field and the time when the flow reaches the end of the field The elapsed time between the initiation of irrigation and the completion of the advance phase Usual units are minutes or hours application efficiency Eq see irrigation efficiency available water AW Soil moisture stored the plant root zone between the limits of field basic intake rate f basin irrigation block end border irrigation bulk density cablegation cfs chemigation consumptive use capacity FC and the permanent wilting point PWP Sometimes referred to as allowable soil moisture depletion or allowable soil water depletion Usual units are inches of water per inch of soil depth The final or steady state infiltration
70. NRCS National Engineering Handbook Part 623 IRRIGATION Chapter 4 Surface Irrigation Contents LIST OF FIGURES E di X THE PRACTICE OF SURFACE IRRIGATION ee e eee eee eee eee eee eee 1 INTRODUCTION 22 135 955 49 9009 0902 1 1 1 1 ourface tO AION MEE M Ea I MENU E esL te A Dd 2 SURFACE IRRIGATION CONFIGURATIONS eee eee eee tasses eee ette tensa esee tette toos 2 1 2 1 Basm ee 3 1 2 1 1 Developmen Ae oe Lies 3 22 Fae AG COMING 3 1 2 1 3 POU CITE 4 1 2 1 4 BS el 8 4 12 15 Since x cx 3 I 2 1 6 Cropping Patterson ted tine de ad ee Ii Mee E iE 5 L2 TE ACE OS TL 5 1 2 1 8 AN 5 L22 6 L224 Deyclopment 7 1222 3 1223 Po
71. VAL SYSTEM Figure I 1 Layout and function of irrigation system components Water must be diverted from a stream captured and released from a reservoir or pumped from the groundwater and then conveyed to the field Excess water needs to be drained from the field Each of these components requires design operation and maintenance of regulating and control structures In order for the system to be efficient and effective the flow not only must be regulated and managed but most importantly it must also be measured Thus the on field component surface sprinkle or drip 15 the heart of the irrigation system And while it is necessary to limit the scope of this Chapter of the NRCS National Engineering Handbook to a guide for the evaluation and design of the surface irrigation system itself it should be appreciated that the surface irrigation system 1s entirely dependent on the other components for its performance 11 1 Surface Irrigation Processes There are three general phases in a surface irrigation event 1 advance 2 wetting or ponding and 3 recession These are illustrated graphically Fig I 2 The advance phase occurs between when water 15 first introduced to the field and when it has advanced to the end Between the time of advance completion or simply advance time and the time when water 15 shutoff or cutoff 1s the period designated as the wetting or ponding phase The wetting or ponding phase will not be present
72. a inputs to the simulation programming The Design Panel is only for interactive design functions and will be discussed separately 41 Entering Field Characteristics The first data the user may wish to define are those associated with the field topography and geometry This panel is shown in Figure II 3 and repeated below in Fig II 5 for the border basin input Inflow Controls Field Topography Geometry Infiltration Characteristics Inputs Design Panel 360 0 Flow Cross Section x ield Length m i Width 1 000 Field Width m 200 0 op Width Field CroszSlope 0 00000 Middle Width 1 000 Border Basin Unit Bottom Width 1 000 Width Row 1 00 ottom Width m spacing m Field System L Maximum Depth m 0 120 Border Basin Irrigation Furrow Irrigation Borders and Basins Downstream Boundary Blocked Manning n Values MEUS pE First Irrigations 0 040 Later Irrigations 0 030 Tax Tmld Base Unit Width Compound Slopes First Slope 0 00800 Manning Equation Calculator 1 Second Slope 0 00800 Slope 0 00000 Rho Third Slope 0 00800 Manning n 0 0000 Sigmal First Distance m 360 0 Fe 0 0000 Sigma Second Distance m 360 0 Depth m 0 0000 Gammal The First Distance is the distance Area m 2 0 0000 Gamma from field inlet to the break in slope Cmh between First Slope and Second Top Width m 0 0000
73. a satisfactory coverage when used to irrigate the whole field simultaneously However the general situation 1s that fields must be broken into sets and irrigated part by part 1 e basin by basin border by border etc These subdivisions or sets must match the field and its water supply Once the field dimensions and flow parameters have been formulated the surface irrigation system must be described structurally apply the water pipes or ditches with 80 associated control elements must be sized for the field If tailwater 1s permitted means for removing these flows must be provided Also the designer should give attention to the operation of the system Automation will be a key element of some systems The design algorithms herein utilized are programmed in the NRCS SURFACE software discussed in Section II This section 1s intended to demonstrate the design and improvement processes IV 3 BASIC DESIGN COMPUTA TIONS The difference between an evaluation and a design is that data collected during an evaluation include inflows and outflows flow geometry length and slope of the field soil moisture depletion and advance and recession rates The infiltration characteristics of the field surface can then be deduced and the efficiency and uniformity determined for that specific evaluation Design procedures on the other hand input infiltration functions including their changes during the season and as flows change flow geometry f
74. abor soil and capital resources The context of this section 1s redesigning surface irrigation systems for improving their performance The term design will be used in the discussion and examples in order to be consistent with historical practice IV 1 THE OBJECTIVE AND SCOPE OF SURFACE IRRIGATION DESIGN The surface irrigation system should replenish the root zone reservoir efficiently and uniformly so crop stress 15 avoided It should provide a uniform and effective leaching application when needed And occasionally it may need to be capable of meeting special needs such as seed bed preparation cooling frost protection and chemigation It may also be used to soften the soil for better cultivation or even to fertilize the field and apply pesticides Resources like energy water nutrients and labor should be conserved The design procedures outlined the following sections are based on a target application depth Zreg which equals the soil moisture extracted by the crop between irrigations The value Zreg 15 equivalent to the soil moisture deficit Design is a trial and error procedure A selection of lengths slopes field inflow rates and cutoff times can be made that will maximize efficiency and uniformity for a particular configuration Iterating through various configurations provide the designer with information necessary to find a global optimum Considerations such as erosion and water supply limitations will act as cons
75. acted from the soil profile oven dried and evaluated on the basis of the dry weight moisture fraction W of the soil sample _ sample wet wt sample dry _ 5 sample dry 5 Vp Va Vy F Soil Volume V Volume of air V Volume of water Volume of Soil Particles Volume of Soil Pores Figure III 1 Components of the soil water matrix The dry weight moisture fraction can be converted to volumetric water content as follows 9 1 6 where 15 the bulk density bulk specific weight of the dry soil Also 15 related to the specific weight of the soil particles by y 1 9 7 Field capacity is defined as the moisture fraction of the soil when rapid drainage has essentially ceased and any further drainage occurs at a very slow rate For a soil that has just been fully irrigated rapid drainage will generally cease approximately after one day for a light sandy soil and after approximately 3 days for a heavy soil This corresponds to a soil moisture tension of 1 10 to 1 3 atm bar The permanent wilting point is defined as the soil moisture fraction at which permanent wilting of the plant leaf has occurred and applying additional water will not relieve the wilted condition This point 15 usually taken as the soil moisture content corresponding to a soil moisture tension of 15 bars The volumetric moisture contents at field capacity
76. ade of the system at specified time intervals The wheel actuated gate shown Fig I 11 can be equipped with a small electric motor and gear assembly to automate the offtake In any event whenever automation can be reduced to single gate as for many borders and basins it is much more feasible and reliable than for furrow systems 15 Ww typical gate structure gate with mechanization Figure I 11 A wheel lift slide gate before and after automation 1 3 5 2 Furrow Irrigation Facilities and Automation Furrows are often supplied water by some of the same facilities used in borders and basins For example shown in Fig I 12 are two furrow systems supplied by ditch gates and siphon tubes 16 Furrow ditch gates Siphon tubes Figure I 12 Two methods of supplying water to furrows Perhaps the most common furrow irrigation system 15 one using gated pipe Two examples are shown in Fig 1 13 to illustrate both the rigid and flexible options Rigid gate pipe 15 generally found in aluminum or pvc and range in size from 6 inch to 12 inches with gate spacings ranging from 20 48 inches The flexible gated pipe or polypipe can be purchased in sizes from 12 to 18 inches with wall thicknesses of 7 10 mil An advantage of flexible gated pipe 1s being able to place gates at any spacing desired In fact occasionally gates are not used at all just holes punched in the pipe Figure I 13 Gate pipe options for furrow irrigatio
77. along with changes in the time of cutoff to achieve a feasible and improved irrigation Figure IV 5 1s the design panel after a trial and error series of adjustments Note that in order to satisfy the constraints on total available flow and duration it has been necessary to divide the field into 18 sets all of which are irrigated in 4 hours using a stream size of 22 5 gpm The irrigation efficiency has been increased from about 47 to about 68 user may at this point wish to see if further improvements can be made Inflow Controls Field Topography Geometry Infiltration Characteristics Hydrograph Inputs Design Panel Input Data for Design Parameters Total Available Flow Total 4455 205 o HELDLAYDHT 4000 gpm Total Total Time Flow is Avaliable irmigation 2 0 As Time hr 56 0 Unit 16 671 fax Ve finn Mis chage Run Length fi 531 Design Flow gonvlint Width Hesults of Sets 22 500 Application Efficiency 6783 Imigation Efficiency 50 Requirement Efficiency 2 99 Distribution Uniformity 94 20 Tailwater Fracton 12 80 Deep Percolation Fracton 19 38 262 Senate Dex Poet inpet Dodo an Pesta Panel Figure IV 5 Improved design for initial irrigations Once the design has been made for the initial intake conditions it needs to be repeated for the later intake conditions This can be accompli
78. and must be computed The first step 1s to estimate the total volume of water that has infiltrated the soil from the data above One way 15 to determine a best fit line through the data and integrate the function multiply by the furrow spacing 2 5 ft and length Another 15 simply to average the depths multiply by the furrow spacing and then by the total field length The result of a sophisticated numerical analysis is a total intake of 1 366 ft and that of simple averaging is 1 372 ft The volume of inflow to each furrow was 13 gpm for 24 hours which translates to 2 502 ft The total tailwater is therefore 2 502 1366 1136 ft or the TWR from Eq 25 is 0 454 or 45 4 Note that precipitation during the irrigation event and perhaps within 1 3 days will also contribute to the total amount of water percolating below the root zone The deep percolation ratio 1s intended as a quantitative measure of irrigation performance and does not include precipitation and thus may not represent all the deep percolation that occurs 62 The next question 15 how much deep percolation occurred Analyses based on a numerical procedure are very helpful for this computation since a partial integration 1s necessary One could estimate the deep percolation graphically as well Using the more elaborate analysis the intake profile 1s integrated between 0 and 990 feet at which point the intake 15 less than the soil moisture deficit and it is assumed that no dee
79. aphy Geometry and Infiltration Characteristics The hydrograph inputs are not required because designs are based on a fixed inflow rate There are then five special inputs for the design process 1 total available flow 2 total time flow 15 available 3 maximum non erosive flow velocity 4 the design flow per unit width and 5 the design cutoff time Note that the design flow per unit width and the cutoff time may be different than the Simulated Unit Inflow and the Time of Cutoff entered into the Inflow Controls table Thus if the calculator button is selected on main window command bar simulation will be different than if the Simulate Design button in design panel 1s selected The flow time of cutoff and run length can be different II 7 1 1 Total Available Flow The field water supply 16 defined by its discharge duration and frequency of availability For design purposes the total available flow entry on the design panel should be the maximum available to the field This should be a relatively reliable maximum since the field configuration will depend on this flow for efficient operations In many cases of surface irrigation the available flow from the delivery system will not efficiently irrigate the entire field at one time or with one set Consequently the field must be partitioned into sets which are irrigated sequentially The number of sets depends on total a
80. available sizes being 6 8 10 and 12 inch diameters Polyvinyl gated pipe 15 rigid like the aluminum pipe easy to install and maintain but will not be as rugged as aluminum and therefore should not have the expected life It does however have a lower initial costs and a wider range of sizes Polyvinyl gated pipe can be obtained for same size of pipe as aluminum but for 15 and 18 inch sizes on special order Lay flat plastic gated pipe has become very popular many locations in recent years Its initial cost is low and it may only be useable for one or two seasons It is the disposable alternative to aluminum and polyvinyl pipe It also comes in wide range of sizes 5 22 inches in diameter and 1s provided rolls of several hundred feet rather than the 20 40 foot lengths of the rigid pipe It 1s thus easier to install and remove On the other hand it is more susceptible to tears and punctures and it is very difficult to remove sediments from the pipe due to its length The offtakes can be installed in the field with simple tools and then replaced with inexpensive plugs if the spacing needs to be changed for other crops Thus the lay flat gated pipe 15 the most flexible terms of use Lay flat tubing has two additional disadvantages First the pressure head that it can accommodate 15 substantially below the value for the rigid pipes and second it is generally necessary to prevent the pipe from moving between irrigations due to wind IV 4
81. ches or feet per minute or hour A device instrument or system to measure infiltration rates Grouping of intake characteristics into families based on averge 6 hour intake rates term often used interchangeably with infiltration rate but technical terms is the process of infiltration when the surface geometry is considered such as in furrow irrigation intake reference flow Qing The discharge at which intake is measured or evaluated in a irrigation efficiency surface irrigation system Usual units are cfs or gpm In general terms the efficiency or performance of an irrigation system 1s measured or expressed as the amount of water used beneficially by the crops divided by the total amount of water made available to the crops In order to provide more specific assistance in evaluating irrigation performance of surface irrigation systems at the field level the following terms have been defined Xll application efficiency E ratio of the average depth or volume of the irrigation water stored in the root zone to the average depth or volume of irrigation water applied to the field Inefficiencies are caused deep percolation and tailwater losses conveyance efficiency C of the water delivered to the total water diverted or pumped into an open channel or pipeline at the upstream end Inefficiencies are caused by leakage spillage seepage operational losses and unaccountable water due to poor measure
82. d fo k A f g WP WP r r A 10 in which WP is the reference wetted perimeter at which the furrow families are defined 115
83. d here as Figures IV 1 and IV 2 The specific uniformity and efficiency terms associated with this irrigation are shown in the Simulated System Performance box in the lower right of the simulation screen T ren 109 Ll E iau re np mu 1000 1100 1208 MiP dana dak Figure IV 1 FreeDrainingFurrow 1 advance recession trajectory Das e anam 20 Figure IV 2 FreeDrainingFurrow 1 tailwater hydrograph 63 The distribution of applied water from the main simulation screen 15 reproduced in Figure IV 3 Flow Depth Surface amp Subsurface Flow Profiles TT mtm tn zreq Intake Figure IV 3 Soil moisture distribution from FreeDrainingFurrow 1 data Here 15 a classic case of a field that 15 too long for the soil intake characteristics Even with a furrow stream of 32 gpm the advance is not completed for almost seven hours At the inlet where the intake opportunity time needed was only 160 minutes to apply the 4 inch depth required the actual depth applied 15 almost 9 5 inches To begin examining alternatives to improve this irrigation open the input tabbed notebook by clicking on the input button S Then select the Design Panel shown in Figure IV 4 input Data for Design DESIR Paranerers Total Avaliable Flow gpm Flow 30236 2 FELD LAYEUT asl in 2400 0 Req d gpm E Total irnigation 80 Time hr 16 671 Os chage gpm Run Leng
84. d to be about equal the savings in tailwater may be nearly offset by increases in deep percolation In terms of automation the practicable ways of implementing cutback are the Cablegation system or surge flow 13 7 Surge Irrigation Under the surge flow regime irrigation is accomplished through a series of short duration pulses of water onto the field A typical advance recession plot for a surged system 15 illustrated in Fig I 15 Thus instead of providing a continuous flow onto the field a surge flow regime would replace a six hour continuous flow set with something like six 40 minute surges Each surge is characterized by a cycle time and a cycle ratio 480 i 400 3601 60 Surge 3 80 Continuous Flow Surge Flow p 40 Surge l 0 40 80 120 160 200 240 Distance From Field Inlet m 280 320 360 400 Figure I 15 Advance and recession trajectories for a surge flow system The cycle time is the sum of an on time and an off time which do not need to be equal The ratio of on time to the cycle time is the cycle ratio Cycle times can range from as little as one minute during a cutback phase to as much as several hours low gradient borders and basins Cycle ratios typically range from 0 25 to 0 75 By regulating these two parameters a wide range of surge flow regimes can be produced to improve irrigation efficiency and uniformity 19 1 3 7 1 Effects of Surging Infiltra
85. do not deal with the initial irrigations following cultivation And second they do not 113 represent the physical condition where water flows over the surface and displaces soil Thus a change in how the families are defined can be made without serious physical limitations 4 00 3 50 4 3 00 Original Basic Intake Values 2 50 6 Hour Avergage Intake Rates Average 6 Hour Intake Rate in hr N 0 00 0 0 5 1 1 5 2 2 5 3 3 5 4 NRCS Intake Family Number Figure A 1 Comparison between the average 6 hour intake rate and the basic intake rate of the original SCS intake families 4 2 Adjusting Intake for Furrow Irrigated Conditions Furrow intake is independent of furrow spacing until the wetting patterns between furrows begin to interact or overlap When the original SCS manuals were written with the furrow adjustments based on the ring infiltrometer equations there were few actual furrow intake measurements and measurement methods in place Thus it was necessary and rational to accommodate furrow irrigation by adjusting one dimensional ring functions in the late 1960 s It is no longer rational because more data are available and more sophisticated analyses have been developed In addition there are now two fundamental pieces of data associated with furrow intake measurements that render Eqs A 8 and A 9 obsolete First the flow of each furrow measurement as well as the actual wetted perime
86. dth on a furrow irrigated field may only be 20 of the water flowing over a similar width in a basin Infiltration is two dimensional through the wetted perimeter rather than a vertical one dimensional intake Furrows can be blocked at the end to prevent runoff but this 15 not a common practice unless they are used in basins or borders to compensate for topographical variation or provide a raised seed bed to minimize crusting problems The distinction between a furrowed basin or a furrowed border and furrow irrigation lies in the semantic preference of the user For purposes of evaluation and design both of these situations would fall under the term furrow irrigation prn A e T p aj E x Amex pou ug prem Figure 1 4 Furow irrigation using siphon tubes from a field bay 1 2 2 1 Development Costs Furrow irrigation systems are the least expensive surface irrigation systems to develop and maintain primarily because minimal land leveling 15 required to implement a furrow system and less precise land smoothing is necessary for maintenance The furrow themselves can be formed with cultivation equipment at the time of planting While less expensive to implement furrow systems are substantially more labor intensive than basins Variations 1n individual flows slopes roughness and intake alter the advance rate of each furrow and there are often substantial differences ho
87. e Field System to furrows by checking the appropriate box Then in the Flow Cross Section boxes enter the channel shape Finally move the cursor to the Manning calculator and enter the respective parameters 11 4 2 Infiltration Characteristics The tabbed notebook where infiltration functions are defined 16 shown in Fig 7 These data comprise the most critical component of the SURFACE software Four individual infiltration functions can be defined 1 a function for first conditions under continuous flow 2 a function for later irrigations under continuous flow 3 a function for first irrigations under surge flow and 4 a function for later irrigations under surge flow The user is referred to Section for a detailed discussion of how these parameters are defined and measured but they are important enough to be given further attention here Note that the model does not allow a cracking term for surge flow since it 18 assumed the cracks will close during the first surge on the dry soil portion of the field 2 The values of and also depend on the units used The SURFACE software only displays the metric values even when English units are used for input 29 Inflow Controls Field Topography Geometry Infiltration Characteristics Hydrograph Inputs Design Panel Tu f x Mog teta Initial Later Continunus Continuous Flow Initial Surge Later Surge Flow Flaw Conditions Conditions F
88. e capacity and availability of the water supply This process can be divided into a preliminary design stage and a detailed design stage IV 2 1 The Preliminary Design The operation of the system should offer enough flexibility to supply water to the crop in variable amounts and schedules and thereby allow the irrigator some scope to manage soil moisture for maximum yields as well as water labor and energy conservation and changes in cropping patterns Water may be supplied on a continuous or a rotational basis in which the flow rate and duration may be relatively fixed In those cases the flexibility in scheduling irrigation 15 limited by water availability or to what each farmer or group of farmers can mutually agree upon within their command areas On demand systems should have more flexibility than continuous or rotational water schedules and are driven by crop demands During preliminary design the limits of the water supply in satisfying an optimal irrigation schedule should be evaluated It 1s particularly important that water measurement be an integral component of the water supply and that it is capable of providing the appropriate depth of water to the field as indicated by Eq HI 24 79 The next step the design process involves collecting and analyzing local climate soil and cropping patterns to estimate the crop water demands From this analysis the amount of water the system should supply through the season can be estimated Co
89. e fields 1s the increased equipment turns during cultivating planting and harvesting operations 1 2 1 8 Land Leveling Before the advent of the laser guided land grading equipment it was common to find surface elevations as much as one or two inches lower or higher than the design elevations of the field Land leveling operators varied in skill and experience Today the precision of land grading equipment is much greater and does not depend nearly as much on operator skill and experience It should come as no surprise that since the field surface must convey and distribute water any undulations will impact the flow and therefore the efficiency and uniformity Basin irrigation is somewhat less dependent on precision field topography than either furrow or border systems because of high flows or the ponding but many users of basin irrigation insist that the most important water management practice they have is lasering Precision land leveling is an absolute prerequisite to high performance surface irrigation systems including basins This includes regular precision maintenance during field preparations land smoothing 1 2 2 Furrow Irrigation Furrow irrigation is at the opposite extreme of the array of surface irrigation configurations from basins Rather than flooding the entire field small channels called furrows and sometimes creases rills or corrugations are formed and irrigated as shown in Fig I 4 The amount of water per unit wi
90. e for the furrow irrigation families since furrow intake 1s proportional to the wetted perimeter and must be adjusted based on the actual flow 1n the furrow The values of the reference wetted perimeter and flow are given in Tables 3 6 Figure III 6 shows the relationship of reference flow to intake family Reference Furrow Dischage e e Reference Flow gpm gt A 0 10 0 00 0 50 1 00 1 50 2 00 2 50 3 00 3 50 4 00 NRCS Intake Family Figure 6 Reference flow for the NRCS intake families 57 TABLE III 7 CONTINUOUS FLOW BORDER BASIN INTAKE FAMILIES INITIAL IRRIGATIONS Continuous Flow Intake Curve Parameterz for Initial Irrigations ID 5011 Hame a k fo Heavy Clay Clay Clay Light Clay Clay Loam Clay Loam Clay Loam Silty Silty Silty Loam Silty Loam Silty Loam Silty Loam Sandy Loam Sandy Loam Sandy Loam Sandy Sandy ft an a 006640 011176 015113 017420 019006 020137 021010 021706 022273 022731 023140 023780 024291 024702 025034 025316 026270 026846 0002155 0004963 0007458 0009411 0010974 0012303 0013420 0014397 0015244 0015996 0016666 0017799 0018729 0019482 0020116 0020637 0022143 0022590 AA coclccocococoococoocooooococco coclccocococoococoocooo
91. e of efficiency can be made This example is a typical exercise as part of a surface irrigation evaluation A number of soil samples from throughout a 65 acre border irrigated field were collected and evaluated gravimetrically The bulk density field capacity and wilting point were estimated for each soil depth during earlier evaluations All the data were averaged by depth and are presented along with the average dry weight soil moisture fraction in the table below How much water should the surface irrigation system apply based on these data 50 Soil Depth Soil Bulk gt W W Density gml The data presented above are presented on a dry weight basis not volumetric basis and need to be converted as follows Soil Depth Soil Moisture D in in 006 0 300 0 163 0 200 1 200 0 364 0 182 0 234 1 404 24 36 0 462 0 210 0 364 4 368 36 48 0 434 0 196 0 392 4 704 Depth Weighted Average Values for two key soil moisture parameters that can be determined from the above data are as follows 1 TAW 0 412 0 195 48 inches 10 416 inches 2 SMD 0 412 0 321 48 inches 4 368 inches or 41 9 of TAW If the irrigation were to occur at this point the volume the system should apply 15 4 368 inches and this will require 4 368 11 12 1n ft 65 ac 23 66 acre feet If the reader works through this example one will note that expressing bulk density in em cm makes 9 a dimensionless number since 1 gm o
92. eDrainingFurrow 2 cfg The FreeDrainingFurrow 2 data describe a 113 acre field supplied by a canal The typical canal flow that 15 available to the field 15 10 0 cfs The field 15 currently irrigated by furrows on 30 inch spacings with a required depth of application of 3 5 inches The soil 15 a clay 43 loam with an average 6 hr intake rate of 0 052 ft ft hr or 0 25 in hr Curve No 0 25 over the 2 5 foot spacing of the furrows An inflow of 0 033 cfs 1s being applied over a 24 hour set time The maximum non erosive velocity was assumed to be 49 ft min The uniformity of this irrigation 1s excellent at nearly 9796 but the application efficiency is poor at only 52 primarily because nearly 40 of the applied water 15 lost as tailwater There 15 about 7 5 percent deep percolation which 15 excessive given the leaching fraction of 5 8 3 FreeDrainingBorder 3 cfe This data set describes a 33 acre field supplied by a well with a capacity of 3400 gpm The soil 15 a clay but with an average 6 hr intake rate of 0 54 in hr part because of a cracking component The field 1s currently irrigated as a free draining border using 1200 foot runs and a unit flow of 13 5 gpm ft The inflow 15 cutoff at 4 hours and before the end of the advance phase The resulting application efficiency 1s 69 The field requires a leaching requirement of 9 but this irrigation configuration produces a 20 deep percolation In addition more than 11 of the inflow resu
93. ed notebook has been included to provide a convenient way to input three important field measurements which might be useful in the three main uses of the software 34 These three field measurements 1 an inflow hydrograph 2 tailwater or runoff hydrograph and 3 advance and recession trajectories On the panel are three mini spreadsheets as shown in Fig II 10 Data in these spreadsheets can be input from or output to Microsoft Excel spreadsheets with simple drag and drop or copy and paste operations Inflow Controls Field Topography Geometry Infiltration Characteristics Hydrograph Inputs Design Panel B A B 1 Inflow Hydrograph 1 Advance and Recession B Tailwater Elapse Inflow 1 Hydrograph Distance Advance Recession Time gpm Elapse Outflow From Time Time mn Ji 17 594 2 mn 26 0 6 0 17 594 206 0 1 427 82 0 3 1 705 0 20 0 16 484 270 0 2 695 164 0 6 9 1 0 56 0 16 167 238 0 3 329 246 1 11 5 715 0 135 0 12 680 318 0 2 695 328 1 15 5 1 0 145 0 12 680 495 0 3 963 410 1 20 5 202 0 12 522 520 0 3 963 492 1 25 4 4 0 256 0 10 778 530 0 4 121 514 1 29 0 T23 5 360 0 11 254 650 0 4 280 656 2 33 5 1 0 5450 0 12 0465 0 000 738 2 38 5 726 5 705 0 000 0 2000 820 2 44 2 1 0 0 000 0 2000 902 2 50 0 728 0 0 000 0 000 984 2 56 3 1 0 0 000 0 000 1065 3 1 0 733 3 0 000 0 2000 1148 3 69 5 1 0 0 000 0 2000 1230 3 735 5 0 000 0 000 1312
94. een furrow border basin configurations This feature 15 provided in the Units Furrow System System software to allow the user to compare the furrow border basin intake parameters for various unit widths furrow geometries and flow rates The simulations can be run from this point if the user wishes to compare furrow and border irrigation performance if the field has a slope or level furrows and basin irrigation if the field 1s level Finally at the right of the intake parameters are three input boxes and a button labeled Two Point The software uses what 15 called the two point volume balance procedure to estimate the a and k or K intake parameters A more detailed explanation of this procedure will be provided later in Section III 3 2 Usually field measurements of advance time to the field midpoint and end are made to adjust intake parameters thus this tool 1s part of the software s evaluation capability 4 3 Inflow Controls T wa Paint TL min 415 0 T 5L min 41 0 OL ft 590 5 The SURFACE programming 15 controlled by the model control parameters as shown in Fig II 9 User input 1s required for three options 1 Simulation Shutoff 2 Inflow Regime and 3 Run Parameters Inflow Controls Field Topography Geometry Infiltration Characteristics Hydrograph Inputs Design Panel Simulation Shutoff Control By Elapsed Time or
95. elow the spreadsheets are three buttons labeled Update Inflow Hydrograph Clicking on each of these buttons 1s necessary to record the data the software arrays for use and storage later Any input data not updated with these buttons will not be available to the computational algorithms of the software nor for later storage files However once updated the hydrographs and trajectories are stored in the cfe file and will reappear upon opening such a file It 1s not necessary to update these data once recorded unless changes are made And it 35 should be noted that any updated data in these spreadsheets will be plotted in the graphic output screens discussed below whenever the Continuous Inflow Hydrograph check box is checked 4 5 Design Panel The interactive design capabilities of the SURFACE software will be discussed in a separate section below It has been included with the input tabbed notebook to facilitate data entry and change during the interactive design process ILS OUTPUT The SURFACE software includes both tabular and graphical display output capabilities Output is accessed from the main screen by selecting Output and then choosing either Display Output Results printed or plotted output from the drop down menu Printed Pletted Results output can be accessed directly by clicking once on the ALD S ds button and likewise plotted output can be directly accessed by the 2 button If the user would like a
96. ems can be made by automating existing control structures and perhaps by a new control structure Generally the surge cycle time for these systems must be 2 4 times as long as in furrow systems to allow complete recession between surges 21 Ill SURFACE NRCS Surface Irrigation Simulation Evaluation and Design Software OVERVIEW The practices of surface irrigation evaluation and design have changed significantly since the first publication of the SCS National Engineering Handbook Section 15 Irrigation Chapters 4 and 5 describing border and furrow irrigation Two generations ago engineers relied on tables nomographs and slide rules to choose a flow and a field length Rules of thumb led to choices of flow length of run and slope A generation ago the slide rule was replaced by programmable handheld calculators and computer models supplemented available tables nomographs Calculation of advance and recession trajectories allowed the irrigation specialist to more accurately evaluate uniformity and efficiency Realistic assessments of the impact of changing flows length and slopes were possible Today the personal computer has replaced all of its predecessors Information is on line and real time Rules of thumb are almost entirely unknown in current curricula and very few graduating engineers have even seen a slide rule Analyses now focus on hydrodynamic zero inertia or kinematic wave models T
97. ences the time water 15 allowed to infiltrate along the field 1ntake opportunity time Low efficiency 1s caused by intake exceeding soil s ability to store it the root zone of the crop deep percolation If the unit flow 15 13 incrementally increased both uniformity and efficiency will increase and this increase will continue in a positive manner for basin irrigation but not for border and furrow irrigation In free draining furrow and most border systems the incremental increase in unit discharge with a corresponding decrease in cutoff time so the volume required 1s approximated will reach a point where the efficiency reaches a maximum and begins to decline even as uniformity continues to increase The cause of this peaking of efficiency 1s the gradual increase in field tailwater that will more than offset the decreases in deep percolation as uniformity improves One of the problems in surface irrigation 15 that the first irrigation of the season following planting or cultivation often requires two or three times the flow rate that subsequent irrigations need to achieve acceptable uniformity infiltration rates are higher during these initial irrigations and thus the need for higher inlet flows As the soil intake diminishes during the season the inlet flows can be reduced Thus the design and operation of surface irrigation systems requires adjusting the inlet flow and its duration to achieve maximum efficiencies 1 3
98. end of the field is not diked Note that neither the advance recession nor the runoff hydrograph are intended to be quantitative as no units are included in the plot These details are presented in the plotted and printed output from the model IL7 DESIGN The SURFACE software includes an interactive field design program located within the input data tabbed notebook This panel is shown in Fig II 15 Inflow Controls Field Topography Geometry Infiltration Characteristics Hydrograph Inputs Design Panel Input Data for Design esum Paraneiers Tota Available Flow apm Flow 30236 2 E FLD PAGS 3600 0 eq d ERES Total Total Time Flow is Avaliable Avrigation 80 Ars Time hr 96 0 fax Unit 23 439 Vern Hmm Dischaqge 42 7 Run Length ft Design Flow gp mt Width Results 32 000 Application Efficiency X 46 91 Efficiency 51 92 Timo mn Requirement Efficiency 998 38 480 0 Distribution Uniformity A 33 48 Tailwater Fracton 1 01 Deep Percolation Fracton 52 08 Run Width ft 2352 ret Arpa Dolo ane fies Desin Figure II 15 The SURFACE design panel 39 II 7 1 Input Data for Design Although the interactive design process does not require all of the data needed for the respective input tables it 1s prudent to enter all of the information for the input tabbed notebook table Inflow Controls Field Topogr
99. es not usually equal the distance between furrows The duration of the water application for border and basin systems 15 usually short enough that the intake rate derived from Eq 13 will not significantly underestimate infiltration at the end of irrigation However it generally will in furrow irrigation systems A more generally applicable relation for furrows is Kostiakov Lewis Equation which adds term for final or basic intake rate f ft min for borders and basins or ft ft min for furrows The Kostiakov Lewis function for furrows 15 14 and for borders and basins is fit 15 It should be noted that will have different values in Eqs 13 and Eq 15 due to width implied as will the values of in Eqs III 12 and 14 For this manual it will be assumed that the exponent a has the same value for both furrow and border basin irrigation The cumulative intake 1n furrow can be expressed as an equivalent depth by Zw 16 where w 1s the furrow spacing However Eq 16 assumes complete later uniformity between furrows which 15 generally not the case Nevertheless it 1s often convenient to express the required intake necessary to refill the root zone as a depth and then determine the corresponding required furrow intake 2 using Eq 16 One note of caution 15 that Eq 16 does not imply that or that f F w These relations are described be
100. ess SCS personnel were making field 112 measurements and attempting to determine intake parameters the late 1960 s these analyses generally centered on adjusting the original intake family coefficients for wetted perimeter Specifically furrow irrigation intake was expressed as z kr 1 8 in which wp is the furrow wetted perimeter feet is the irrigated furrow spacing in feet The wp w adjustment was limited to a value no greater than 1 0 A substantial effort was made to express wetted perimeter as a function of flow Manning n furrow slope and furrow shape Values of Manning were typically 0 03 or 0 04 and the furrow shape was generally represented as trapezoidal The concept of a furrow based basic intake rate was maintained In the end the concept of relating basic intake rates in cylinder and furrow tests was abandoned Instead a fairly large number of values of wetted perimeter were computed using trapezoidal shapes ranging from a 0 2 ft bottom width and 1 1 side slopes to 0 5 ft bottom widths with 2 1 side slopes Values of flow slope and Manning were included in the analysis The data were then simulated by the following relation 0 0 4247 wp 0 2686 0 0462 9 JS where wp 15 the wetted perimeter in feet is the flow in gpm 5 1s the furrow slope and 15 the Manning n The differences between lateral and vertical infiltration were introduced by adjusting the 0
101. evel iterative procedure Assuming a furrow configuration for purposes of demonstration the first level uses a volume balance computation 1 600 1 A x to Kt x Ft x t III 49 1 r in which is the inflow per unit width or per furrow at the upstream end of the field cfs tx 15 time since inflow was initiated 1n min 15 the surface flow shape factor A is the flow cross sectional area at the flow s upstream end at time tx in ft x 1s the distance from the inlet that the advancing front has traveled in f minutes ft o 15 the subsurface shape factor described by atr 1 t1 Inge 50 where 15 the exponent in the power advance equation Eq III 41 The value of o is generally assumed to be constant with values between 0 75 and 0 80 However its value actually changes with field slope flow shape slope of advance trajectory and field length At the time of the writing of this manual no general guidelines were available for selecting a value of o except that to assume it has a constant value of 0 77 temporary estimation 1s provided as follows but users of this manual should be aware that new information will provide a better approximation in the future The flow velocity at the advancing front when it has reached the field midpoint can be found by differentiating Eq 41 and then dividing the result by the average velocity at the inlet to define a dimensionles
102. f maximum discharge and head As an example recall that in the example present in Section V 3 1 1 a furrow flow of 22 5 gpm was suggested From Table IV 1 it can be noted that when the head on the siphon or spile 15 about one foot or less a 2 1nch tube diameter should be selected If the head 1s one foot or greater the tube diameter can be reduced to 1 5 inches Another example using the information from Section IV 4 above is also illustrative suppose the diversion from the ditch 1s to be accomplished by siphon tubes and assume further the elevation of the water surface in the field 1s equal to the non diked water elevation The head on the siphons would therefore be the maximum water surface elevation in the ditch at a depth of 2 7 feet minus the field elevation of the field water surface at a ditch depth of about 2 feet or 0 7 feet or about 8 inches From Table IV 1 six inch siphons would carry about 350 gpm and thus 1 would require 13 such siphons to divert the 10 cfs 4490 gpm ditch flow A better and less labor intensive solution would be either larger ditch gates or check outlets both of which are discussed below IV 4 1 2 Sizing Small Ditch Gates small ditch gates as illustrated 1n Fig IV 16 typically have round entrances and may be flush with the ditch side or recessed and vertical The conduit through the ditch berm is also circular as a rule and submerged at the field side making the offtake a submerged orifice Commercial s
103. f water has a volume of 1 This allows the evaluator to express the equivalent depth in any units desired III 2 2 Infiltration 2 2 1 Basic Theory Infiltration 15 perhaps the most crucial factor affecting surface irrigation This parameter controls the amount of water entering the soil and secondarily impacts the duration of both advance and recession In other terms infiltration has an important impact on the duration of the irrigation itself Unfortunately infiltration exhibits very large variability over field and 15 51 difficult to characterize on a field scale because of the large number of measurements generally necessary One of the simplest and most common expressions for infiltration 1s the Kostiakov Equation which can be written general terms for furrow irrigation as 7 12 which 7 is the cumulative volume of infiltration per unit length ft ft The coefficient K has units of ft ft min while a is dimensionless The intake opportunity time ft has units of minutes In a border or basin where a unit width can also be defined infiltration 1s expressed as z kr 13 where 2 is the cumulative depth of infiltration ft the coefficient has units of ft min and a is dimensionless as before The units of Eqs III 12 and III 13 must be different since a unit width such as that used for borders and basins cannot be used for furrow systems The wetted perimeter of the furrow do
104. factors affecting furrow irrigation are the same as those noted previously for basin irrigation higher labor requirements require resource in US agriculture that is becoming critically short The lower efficiencies are problematic in an era of diminishing supplies competition by urban needs and the detrimental impact of salts and sediments on the quality of receiving waters when efficiencies are low When polypipe 15 used to distribute water to the furrows an environmental concern with its disposal is raised On other hand furrow irrigation 15 more flexible than either borders or basin as the configuration 15 easily changed by simply increasing or decreasing the number of furrows being irrigated simultaneously or by irrigating alternate furrows 1 2 2 8 Land Leveling While precision land leveling 1s not as critical to furrow irrigation as 1t 1s to basin and border irrigation an irrigator cannot expect to achieve high uniformities and efficiencies without it Precision land leveling will reduce the furrow to furrow variations in advance times and will improve both uniformity and efficiency Land leveling for furrow systems is also much less intrusive since field slopes can run in both field directions thereby reducing the volume of soil that has to be moved Land smoothing while not as important is nevertheless a good practice on a regular basis 1 2 3 Border Irrigation Border irrigation looks like basin irrigation and operate
105. fety checks are made to insure that the appropriate characteristics of the surface irrigation system are defined simulation programming utilizes a fully hydrodynamic analysis of the system Input data options are provided to increase or decrease the execution speed to suit the visual appearance of the graphics screen that presents the simulation results time step by time step A more detailed discussion of the simulation functions will be given later along with some example problems 11 3 6 Design The Design option on the main menu bar will open the input data tabbed notebook to the Design Panel This can also be accessed through the input options noted earlier The design programming allows the user to simulate and modify various design configurations in an interactive mode IL4 DATA INPUT Providing input data to the SURFACE software involves two activities 1 defining the characteristics of the surface irrigation system and 2 defining the model operational control parameters 25 The input tabbed notebook shown earlier as Fig II 3 be accessed from the Input menu command or the speed button The tabs are from left to right 1 Inflow Controls 2 Field Topography and Geometry 3 Infiltration Characteristics 4 Hydrograph Inputs and 5 Design Panel Input data for the first three panels are required for all applications of the SURFACE software The fourth Hydrograph Inputs 1s an optional feature to allow field dat
106. gns described above the flow required was less than the total available This assumes the supply flow rate 15 flexible If the design processes are repeated with the delivery fixed at 2 400 the efficiency at the field level might be reduced considerably the case of the FreeDrainingFurrow example setting the Design Flow to 22 86 gpm for the initial irrigations reduces the irrigation efficiency by only one percent The later irrigations in this case are not a serious problem By reducing the unit flow to 7 62 gpm it is possible to accommodate the entire 2 400 gpm supply and achieve about the same application efficiency of nearly 72 IV 3 1 2 Example Free Draining Border Design In an open instance of SURFACE load the FreeDrainingBorder 4 cfg and execute simulation for the initial irrigation conditions Figures IV 7 and IV 8 show the advance and recession trajectories and the tailwater hydrograph The resulting soil moisture distribution shows that most of the border length was under irrigated The application efficiency 15 only 3995 primarily due to a 43 loss of tailwater The 10 leaching fraction 15 more than satisfied with a nearly 17 deep percolation loss Both the unit discharge and the time of cutoff time are too large By iteratively reducing unit inflow and the duration of the irrigation it 15 possible to substantially improve the performance of this irrigation In this case it is not necessary to adjust the field
107. h the primary supply VON 6 01 in which N 1s the number of unit widths or furrows that can be irrigated by the reuse system and Nr is the total unit widths or furrows in the field And 94 IV 3 4 1 F N w JV ena IV 7 where F is the field width in feet 15 the number of furrow or unit widths to be irrigated by the main water supply and w is the unit width or furrow spacing in feet Steps 1 3 should then be repeated with an adjusted field width equal to the actual width F minus the width of the field to be irrigated with the recycled tailwater w The application efficiency E of this system 15 Sre F L E 100 IV 9 maximum volume of tailwater reservoir would be equal to the total volume of recycled tailwater NpQotco 1f the reuse system only operates after the primary supply has been shut off or directed to another field A smaller reservoir is possible if the recycling can be initiated sometime during the irrigation of the main sets Unless land 15 unavailable the simplest system uses the maximum tailwater storage The tailwater during later irrigations may not be greater than during the initial irrigations However performing the design for both is since the capacity of the tailwater reservoir will be dictated by the maximum runoff Example Furrow Tailwater Reuse Design As an example of this procedure consider the FreeDrainingFurrow
108. has been cut in half Likewise by clicking on the buttons of sunzenott the horizontal up down button the field width can be ss subdivided In this case the field has been subdivided into 4 IDEO width sections Each rectangular subdivision represents one set the irrigation scheme in the case here there 8 sets Run Vidi m The easiest way to interactively design a surface 2n irrigate field with the SURFACE software 15 to determine the most efficient unit discharge and then subdivide the field until the constraints on total available supply and total available time are satisfied This will be demonstrated in a following section In many situations the fields that require re design have irregular shapes It may be necessary to partition the field into two or more separately managed units to achieve a square or rectangular layout In other cases it may be necessary to design for a single field dimension like the average run length or a set of average run lengths corresponding to the dimensions of the expected set layout It 15 always good practice to evaluate the extreme conditions like the maximum and minimum run lengths to anticipate the management problems the irrigator will face II 7 3 Simulation of Design The interactivity of the SURFACE design programming 15 accessed by clicking on the Simulate Design button at the bottom of the design panel The run time advance recession tailwater hydrograph and results wil
109. have proven to work well during field research and demonstration studies Cablegation involves mechanized plug attached to a cable which is extended at a fixed rate from the upper end of the system The flows from gated openings near the plug have higher rates than those away from the plug and thus as the plug moves along the pipe the flow in the upstream furrows decrease Figure I 14 shows a schematic of a typical Cablegation system Cablegation is an interesting form of a more general concept called cutback irrigation Cablegation has not found widespread use due to its complex hardware difficult management requirements and lack of standardized and commercial equipment Pipe cross sections showing water levels upstream from plug Plug has no Flow almost plug influence stopped 6b maximum flow Ba Reel for cable with speed control 15 o ee EE Am ater level 7 77 Being irrigated PVC pipe partially Traveling Outlet or fully buried plug 25 oy To be irrigated Figure 1 14 Schematic Cablegation system 16 As a concept cutback is an attractive way to improve furrow irrigation performance practice it 15 almost impossible to implement field and it 1s inflexible Of course with simple furrow irrigation system using siphons it can be done with substantial labor But since the advance time and wetting time nee
110. hecking the Continuous Flow w Cutback box and inputting 0 60 for the value of Cutback Ratio and 1 05 for 9 the CB Length Fraction Atter looking at the data click on the run button El The simulated flow will complete the advance phase and then the inflow will be reduced resulting in the tailwater hydrograph shown in Fig 12 fate 5 Tiris Houe Figure IV 12 Simulated tailwater hydrograph using the CutbackDesign cfg data file If the cutback ratio 1s too small the reduced inflow wave will reach the end of the field and the downstream end of the field will dewater For example set the cutback ratio to 0 50 and repeat the simulation The version of the SURFACE software provided at the time of this manual cannot simulate this condition reliably Consequently an alert such as shown below will be presented on the screen as shown below and the simulation stopped instructed the user should adjust either the Cutback Ratio or the CB Length Fraction until the downstream does not dewater 92 Mrcs surface Cutback Dewatered the downstream end of the Field You will need increase the value of the Cutback Ratio and or increase the the Cutback Length Fraction IV 3 4 Design of Systems with Tailwater Reuse The efficiency of free draining surface irrigation systems can be greatly improved when tailwater can be captured and reused If the capture and reuse 1s to be applied to the field currentl
111. iated the application efficiency would decrease to 51 as the tailwater losses increase from 21 to about 49 of the total inflows The soil of this field is a clay loam with an average 6 infiltration rate of 0 ft ft hr or 0 24 in hr Curve No 0 25 over the 2 5 foot spacing of the furrows The target applied depth is 2 5 inches which is not quite satisfied There is also a 5 leaching to consider 45 Surface Irrigation Evaluation INTRODUCTION An evaluation of a surface irrigation system will identify various management practices and field layouts that can be implemented to improve the irrigation efficiency and or uniformity The evaluation may show for example that achieving better performance requires a reduction in the flow and duration of flow at the field inlet or it may indicate that improvements require changes the field size and topography Perhaps a combination of several improvements will be necessary Thus the most important objective of the evaluation is to improve surface irrigation performance The procedures for field evaluation of irrigation systems are found in the NRCS National Engineering Handbook Part 652 National Irrigation Guide particularly Chapter 9 Irrigation Water Management This section will not attempt to repeat each of the various procedures applicable to surface irrigation but to supplement some of them in more detail or with more recent developments IIL2 SOME IMPORTANT SURFACE
112. ield slope and length to compute advance and recession trajectories the distribution of applied water and tailwater volumes or pond The design procedures also determine efficiencies and uniformities However the design process can be applied to many more field conditions than an evaluation to determine efficiencies and uniformities through of the surface irrigation model NRCS SURFACE There are five basic surface irrigation design problems Free draining systems Blocked end systems Free draining systems with cutback Free draining systems with tailwater recovery and reuse and Surge flow systems i ui ad ox The philosophy of design suggested here 15 to evaluate flow rates and cutoff times for the first irrigation following planting or cultivation when roughness and intake are at their maximums as well as for the third or fourth irrigation when these conditions have been changed by previous irrigations This will yield a design that will have the flexibility to respond to the varying conditions the irrigator will experience during the season of the specific data required for design were enumerated in Section II IV 3 1 Free Draining Surface Irrigation Design All surface irrigation systems can be configured to allow tailwater runoff However this reduces application efficiency may erode soil from the field or cause similar problems associated with degraded water quality It is therefore not a desirable surface irrigation conf
113. iency of 66 The 5 leaching fraction 1s exceeded by a deep percolation of about 33 8 6 Basin 5 The Basin 5 data comes from a 19 7 acre field irrigated by a canal water supply limited to 5 3 cfs over a 48 hour period The soil has a 6 hour intake rate of 0 95 inches hour which 15 typical of silt loam soil The target depth of application 15 4 inches 44 A simulation of the data as given shows an application efficiency of about 57 due primarily to a deep percolation loss of about 4396 The flow barely completes the advance phase in the 7 hours of application so there 15 also substantial under irrigation near the downstream end of the basin 8 7 Basin 6 cfe The Basin 6 data comes from a large 193 acre basin system with a clay soil the average 6 hour intake rate 1s 0 47 in hr An irrigation district supplies water to the field with an upper limit on flow of 16 cfs and availability of 96 hours per irrigation Under present operations the application efficiency 15 about 63 5 leaching requirement is exceeded by a deep percolation loss of more than 36 of the inflow 8 8 CutbackDesign cfg A furrow irrigated field of about 21 acres is supplied by a well with a capacity of 1200 gpm Each furrow 15 initially irrigated with a flow of 14 gpm which 15 reduced to 8 4 gpm after the advance phase is completed The total set time is 12 hours and the resulting application efficiency 15 more than 79 If the cutback is not init
114. if the inflow is terminated before the advance phase 15 completed a typical situation in borders and basins but a rarity in furrows The wetting phase 1s accompanied by tailwater runoff from free draining systems or by ponding on blocked end systems After the inflow 1s terminated water recedes from the field by draining from the field and or into the field via infiltration This 1s the recession phase numerical models of surface irrigation attempt to simulate these processes Time of Recession Recession Time of Cutoff Wetting or Ponding Time of Advance Advance Phase Time since Irrigation Started Distance from Field Inlet Figure 1 2 The basic phases of a surface irrigation event L2 SURFACE IRRIGATION CONFIGURA TIONS Choosing a particular surface irrigation system for the specific needs of the individual irrigator depends on the proper evaluation and consideration of the following factors 1 costs of the system and its appurtenances 2 field sizes and shapes 3 soil intake and water holding characteristics 4 the quality and availability timing of deliveries amount and duration of delivery of the water supply 5 climate 6 cropping patterns 7 historical practices and preferences and 8 accessibility to precision land leveling services 1 2 1 Basin Irrigation Basin irrigation is distinguished by a completely level field with perimeter dikes to control and or prevent runoff
115. iguration However where water is inexpensive the costs of preventing runoff or capturing and reusing it may not be economically justifiable to the irrigator In addition ponded water at the end of the field represents a serious hazard to production if the ponding occurs over sufficient time to damage the crop scalding Furrow irrigation systems normally allow the outflow of tailwater Tailwater outflow from border systems is less common but remains a typical feature As rule tailwater runoff is not a feature included in basin irrigation except as an emergency measure during high rainfall events or when the irrigators over fill the basin Thus the design algorithms herein for free draining field conditions apply primarily to furrow and border systems 81 The basic design procedures for free draining systems involve eight steps 1 identify the field control point 2 determine the required intake opportunity time Treg 3 select a unit flow and compute the advance time tz 4 compute the cutoff time 5 evaluate uniformity and efficiency 6 iterate steps 1 5 until the optimal system is determined usually on the basis of maximum irrigation efficiency subject to a lower limit on storage efficiency 7 repeat the design computation for the later irrigation conditions 8 configure the field into sets that will accommodate the water supply and 9 determine how to uniformly apply water using pipes ditches and contro
116. igurations for the project is in fact an integral part of the project planning process In either case the data required fall into six general categories These were noted in Section I and are provided here for emphasis l the nature of irrigation water supply in terms of the annual allotment method of delivery and charge for water discharge and duration frequency of use and the quality of the water 2 the topography of the land with particular emphasis on major slopes undulations locations of water delivery and surface drainage outlets 3 the physical and chemical characteristics of the soil especially the infiltration characteristics moisture holding capacities salinity and internal drainage 4 the cropping pattern its water requirements and special considerations given to assure that the irrigation system 1s workable within the harvesting and cultivation schedule germination period and the critical growth periods 3 the marketing conditions in the area as well as availability and skill of labor maintenance and replacement services funding for construction and operation energy fertilizers seeds pesticides etc and 6 the cultural practices employed in the farming region especially where they may constrain a specific design or operation of the system IV 2 THE BASIC DESIGN PROCESS The surface irrigation design process is a procedure to determine the most desirable frequency and depth of irrigation within th
117. ime Another alternative is to use expanding cycles for example if the Variable Surge Flow box 15 selected and a value of 15 minutes 15 entered into the Surge Adj Time box and the number of surges reduce to 4 the application efficiency can be increased another 6 97 0 100 200 300 400 500 600 700 800 900 1000 1100 1200 Distance along Field feet Figure IV 15 Surge flow advance and recession plot for FreeDrainingFurrow 1 example IV 4 HEADLAND FACILITIES Water supplied to the surface irrigation system is distributed onto the field by various combinations of head ditches or pipelines equipped with outlets such as gates siphons spiles and checks Some of these are illustrated in Section I and are collectively known as headland facilities The design of surface irrigation headland facilities should satisfy three general criteria 1 the water supply to the system must be distributed onto the field evenly 2 the capacity of the headland facilities must be sufficient to accommodate the supply discharge and 3 the headland facilities should prevent erosion as the flow emerges onto the field It 1s not necessary for the individual outlets to be calibrated and capable of measuring flow but they should be adjustable enough to regulate the outlet flows IV 4 1 Head Ditch Design A number of standards and manuals exist for the design of open channels and these should be reviewed in designing surface irrigation head ditches This par
118. infiltration rates independently of Tables III 7 10 The second case occurs where intake coefficients might be modified 1s where one wishes to delineate the effects of wetted perimeter variations along a furrow The basic argument for not making this adjustment 15 that simultaneous adjustments must also account for varying roughness and cross section both of which tend to minimize the effect of wetted perimeter And the third case occurs when the furrow infiltration coefficients have been defined using furrow advance data and derived from one value of inflow slope length of run etc but then the simulation or design analysis 1s based on a different values of field parameters This 1s the most important of the three possible reasons for adjusting infiltration coefficients since improving simulation or design capabilities inherently implies field definition of infiltration The infiltration coefficients a and in Tables III 3 III 6 and Eq III 14 are defined 76 for furrow irrigation at a specific discharge and therefore a specific wetted perimeter If the simulated flow 15 significantly different from the discharge where infiltration 1s defined intake coefficients should be adjusted Although there are a number of studies that have examined ways to adjust infiltration for wetted perimeter most require a substantially more rigorous treatment of infiltration than can be accommodated here Consequently a relatively simple ad
119. ing borders or basins also reduces the effect of topographical variations Some soils are too coarse textured for efficient surface irrigation but practices armed at incorporating crop residues and animal manures not only change intake rates but also 1mprove soil moisture holding capacity When water advance over a freshly cultivated field 1s a problem due to high intake a limited discharge or an erosion problem the surface 1s often smoothed and compacted by attachments to the planting machinery 1 3 4 Tailwater Recovery and Reuse In order to convey water over the field surface rapidly enough to achieve a high degree of application uniformity and efficiency the discharge at the field inlet must be much larger than the cumulative intake along the direction of advance As a result there remains a significant fraction of the inlet flow at the end of the field which will run off unless the field is diked or the tailwater 15 captured and reused In many locations the reason to capture tailwater 15 not so much for the value of the water but for the soil that has eroded from the field surface Other 14 conditions exist where erosion is not a problem and the water supply is abundant so the major emphasis 15 merely to remove the tailwater before waterlogging and salinity problems emerge Finally it may be cost effective to impound the tailwater and pump it back to the field inlet for reuse or store it for use on lower lying fields A typical tailwate
120. it width or volume per furrow spacing of water necessary to replace the soil moisture deficit V 15 the depth of water per unit width or volume per furrow spacing of irrigation water that 1s actually stored in the root zone Vai 1s the depth of water per unit width or volume per furrow spacing that represents under irrigation Vap 15 the depth of water per unit width or volume per furrow spacing of water that percolates below the root zone 15 the depth of water per unit width or volume per furrow spacing of water that flows from the field as tailwater Vy is the depth of water per unit width or volume of per furrow spacing of water needed for leaching Vig 15 the average depth per unit width or volume per furrow spacing of infiltrated water the least irrigated 25 of the field 2 3 1 Irrigation Efficiency The definition of irrigation efficiency represents the fraction of water applied to the field that could be considered beneficially used y V V V III 20 V tV in 2 3 2 Application Efficiency Application efficiency 1s a subset of irrigation efficiency which evaluates only how well the irrigation water was stored in the root zone V V eu z 21 Vin Es Vp ru III 2 5 3 Storage or Requirement Efficiency A measure of how well the root zone was refilled is called storage or requirement efficiency and 15 described as V
121. ith a 16 inch pipe The pressure head at the 90 turn into the field is 6 feet Three valves are situated at the upper to regulate flow to the left and right branches of the gated pipe as well as to control to the lower section At the mid section of the field a two way valve can be located to shift the flow into the right or left branches The gated pipe sections extend in either direction for 1180 feet From Fig IV 18 a flow of 22 5 gpm will require a head of about 0 6 feet Thus the friction gradient computed from Eq IV 11 for the pipes running uphill 1s 6 0 0 0001 x 1180 0 6 h M 0 448 fi 100 ft 1180 100 From Table IV 4 the gated pipe should be at least 16 inches in diameter Generally pipe this big could only be supplied as lay flat plastic tubing Control Valve d Inlet Valve SES BBB ee Buried Mainline Gated Pipe Run Length 591 Run Width 252 Figure IV 19 Layout of FreeDrainingFurrow 1 gated pipe system It may not be desirable to use large diameter lay flat diameter gated pipe In order to reduce the diameter and allow the irrigator a choice between aluminum and lay flat pipe the main supply pipes need to be reconfigured 108 Figure IV 20 shows an alternative design which the gated pipe layout is subdivided in order to reduce the size of the pipe In this case the supply pipes still carry the entire 2 400 gpm and are the same diameter as above There are nearly 1 200 feet
122. izes from 2 inches to 24 inches are available For 6 inch and smaller the design 15 the same as siphons and spiles detailed in Section IV 4 1 IV 4 1 5 Sizing Check Outlets and Large Ditch Gates A typical check outlet was shown Fig IV 16 They are usually equipped with simple slide inserts to close the opening when not in use although many check outlets are situated above the water level of the normal water flow the ditch These outlets normally operated at or near a free flow regime and therefore their flows are dependent only on the water level the ditch The head on these outlets 1s defined as the difference between the water elevation in the ditch and the elevation of the check crest 101 b Figure IV 17 Typical operational conditions of surface irrigation siphons and spiles TABLE IV 1 MINIMUM RECOMMENDED SIPHON AND SPILE SIZES FOR SURFACE IRRIGATION SYSTEMS
123. justment 15 used Using From Eqs III 27 III 28 and 30 the wetted perimeter be extracted and defined for the flow where the coefficients are determined 72 0 4529 0 72 7 1 07 56 of I where is the flow where the infiltration coefficients have been determined in ft min and WP 1 the corresponding wetted perimeter in ft Then the coefficient 6 is defined as WP Infilt m m 57 in which WP 15 the actual wetted perimeter at the field inlet Then the Kostiakov Lewis equation 15 revised by multiplying and parameters by 7 Ke 58 3 2 5 General Comment The adjustment of infiltration for wetted perimeter variation along furrow 15 one topic of interest to model developers It has generated some interesting debate On one hand the wetted perimeter 1s known to vary along the furrow with the decreasing flow and should be adjusted accordingly at each computational node This concept 1s technically correct so far as discharge variation 1s concerned but relies also on the assumption that hydraulic roughness and cross section are constant along the furrow an assumption that 1s known to be weak The other side of the argument 15 that two other important parameters are varying in a fashion compensates for the diminishing discharge along the furrow The roughness increases along the furrow as the effects of less water movement produces less s
124. l keep the water from concentrating in one location of the field With precision land grading a border flow will advance uniformly to the end of the field and apply a uniform and efficient irrigation Land smoothing to maintain the surface profile 15 also important 11 One of the interesting features of borders as with furrows 15 that the field slope does not need to be the same In some heavy soils the slope can be flattened over the lower 25 of the border to increase uniformity at the end of the field 1 2 4 Summary of Surface Irrigation Methods Choosing one type of surface irrigation over another 1s very subjective because of the number of criteria to consider and the complicated interactions among the criteria Table 1 below gives a general summary of the discussion above and some typical comparsions TABLE I 1 A GENERAL COMPARISON OF SURFACE IRRIGATION METHODS Selection Criteria Furrow Irrigation Border Irrigation Basin Irrigation Development Costs Field Geometry Amount and Skill of High labor and high Moderate labor and Low labor and Labor Inputs Required skill required high skill required moderate skill required Land Leveling and Minimal required but Moderate initial Extensive land Smoothing needed for high investment and leveling required efficiency regular smoothing 15 initially but Smoothing needed critical smoothing is less regularly critical if done periodically Soils Light to moderate Moderate to heavy M
125. l shown on the main screen The results will also be posted on the design panel as noted below During the design simulation the input tabbed notebook will be hidden until the simulation is Some esa completed If the simulation 15 interrupted the user will need to click on the button to make the tabbed notebook re appear Iteratively choosing the design flow cutoff time and then if necessary the run length will allow the user to develop designs that produce maximum efficiencies and uniformities 42 II 7 4 Results Each design simulation produces an estimate of its Results performance with six indicators Application Efficiency 2 75 18 Irmigation Efficiency 81 51 l Application Efficiency the percentage Of the Requirement Efficiency X 99 14 field delivery that was captured in the root zone of Distribution Uniformity X 95 05 the crop Tailwater Fracton 16 43 Deep Percolation Fracton 8 38 2 Irrigation Efficiency an extension of Application Efficiency to include leaching water where a leaching fraction has been specified 3 Requirement Efficiency the percentage of the root zone deficit that 15 replaced during the irrigation 4 Distribution Uniformity the ratio of applied water in the least watered 25 of the field to the average over the entire field 5 Tailwater Fraction the fraction of applied irrigation water that runs off as tailwater and 6 Deep Percolation Fraction the frac
126. lay Light Clay Clay Clay Clay Loam Loam Loam Silty Silty Silty Silty Silty Silty Sandy Sandy Sandy Loan Loam Loam Loam Loam Loam Loam Sandy Sandy Sandy ID 5011 Hame Clay Clay Clay Light Clay Clay Clay Clay Loam Loam Loam Silty Silty Silty Silty Silty Silty Sandy Sandy Sandy Loam Loam Loam Loam Loam Loam Loam Sandy Sandy Sandy amp d IRRIGATIONS k Etran aj 005820 009766 013223 015250 016616 017617 018370 018976 019483 019881 020250 020810 021251 021602 021894 022146 022980 023486 024461 D 005310 008936 012083 013950 015196 016107 016810 017356 017803 018181 018500 019020 019431 019752 020024 020256 021020 021476 022361 D D D D DDD fo itan 0001831 0004208 0006338 0007990 0009333 0010449 0011407 0012238 0012950 0013589
127. length since advance 15 relatively rapid Figure IV 9 shows the design panel after several iterations The irrigation efficiency has been improved to about 73 and the leaching requirement has been met on average although not uniformly The irrigation set time has been decreased to 3 hours from the original 4 hours and the unit inflow has been reduced from 0 036 cfs ft to 0 026 cfs ft 86 a 100 E 400 Sieh 500 Field feed Figure IV 7 FreeDrainingBorder 4 advance and recession plots for initial irrigations 1 4 5 T amp 9 10 1 12 13 Figure 8 Tailwater hydrograph for FreeDrainingBorder 4 data 87 Inflow Controls Field Topography Geometry Infiltration Characteristics Hydrograph Inputs Design Panel x Input Data for Design Design Parameters Total Flow E FELD LAYLI Total Available Flow Reg d cfs ES Total Total Time Flow is Avaliable irrigation 20 0 hrs Timo hr 46 0 Unt 4r 157 Max Ver fimm 40 0 cis Run Length fi 820 Design Flow Width Results No of Sets 0 009 Application Efficiency X 62 11 2 Irrigation Efficiency 58 12 Cuttoff Timo mmn 00 0 Requirement Efficiency Distribution Uniformity 5 g2 74 Tailwater Fracton 28 58 Deep Percolation Fracton 9 31 Run Width 656 ant Jape Data dis Desig Pa
128. locked end surface irrigation system 15 in determining the cutoff time In practice the cutoff decision 1s determined by where the advancing front has reached This location may be highly variable because it depends on the infiltration characteristics of the soil the surface roughness the discharge at the inlet the field slope and length and the required depth of application Until the development and verification of the zero inertia or hydrodynamic simulation models there were no reliable ways to predict the influence of these parameters or to test simple design and operational recommendations d Figure IV 10 Stages of a blocked end irrigation One simplified procedure for estimating the cutoff time 15 based on the assumption that the field control point 1s at the field inlet for blocked end systems By setting the field control point at the upstream end of the field the cutoff time 1s approximated by the intake opportunity time Teg and is independent of the advance time specific cutoff time feo may be 69 adjusted for depletion as follows KT IV 3 co req where x is a simple fraction that reduces tco sufficiently to compensate for the depletion time As a rule would be 0 90 for light textured sandy and sandy loam soils 0 95 for medium textured loam and silty loam soils and 1 0 for clay and clay loam soils The volume of water the designer would like to apply to the field 1s as follows
129. low since surface irrigation 1s often applied to the heavier soils and some of these tend to crack Eqs III 14 and III 15 can be extended to include a combined term for cracking and depression storage c C 17 52 18 The units of c and are same as 2 Z respectively To date there no general recommendations for the cracking terms One can observe that if f is set to zero Eq III 17 has the same form as the NRCS infiltration family equations pedis 19 1 2 2 2 Revised NRCS Intake Families The original SCS intake families based on Eq 19 with a fixed c value have provided users with a starting point in the design and evaluation of surface irrigation systems These original intake family curves are revised in this manual to correspond to Eqs III 14 and III 15 In order to provide the revised families that are typical of values found in field measurements there are several assumptions that have been made The availability of data in form of Eqs III 14 and 15 is much greater for furrow systems than for either borders or basins Consequently the reference family structure is formulated for furrow irrigation and then modified for borders and basins 2 The intake families should encompass both initial and later irrigations since the intake characteristics are usually reduced after the first irrigation The reference family of curves is for
130. low Conditons Conditions Twa Faint 0 356 0 000 0 259 0 000 min k m mn a 0 00967 0 00000 0 01240 0 00000 a min fo 0 000587 10 000000 0 000518 10 000000 00 c m 0 00000 0 00000 m infilt_ 0 0 Ips 2 000 2 000 Tables Tables T ables _Tables Simulate Root one Soil Moisture Depletion zreq meters 0 100 0 000 0 100 0 000 Required Intake Opportunity Time min Units of Measure English cfs Surface Imigation Configuration English gpm Border Basin Irrigation C Furrow Irrigation Figure II 7 The Infiltration Characteristics panel of the input tabbed notebook Just below the four intake parameters are two boxes labeled Qinfilt which are used to enter the flow at which the intake parameters are defined Furrow intake parameters are always defined for a unique flow whereas border and basin parameters are not The SURFACE software uses the values of Qinfilt to adjust furrow intake parameters for changes in flow Note that Qinfilt boxes are not provided for the surge flow conditions as they must be the same as the respective continuous flow value In other words the Qinfilt value for the initial surge flow condition 1s assumed to the same as that for the initial continuous flow condition It 15 not necessary to define infiltration for each of the four conditions However they must be defined fo
131. ls At the end of this procedure the designer should consider whether or not the field geometry should be changed reducing the run length for example or perhaps targeting a different application depth Since the design computations can be made quickly the designer should examine a number of alternatives before recommending one to the irrigator The location of the field control point 15 where the minimum application will occur In free draining furrows this point is at the downstream end of the field In borders the field control point may be at either end of the field depending on the recession processes and cannot be determined until the irrigation regime is simulated by the SURFACE software The cutoff time is approximated by the sum of the required intake opportunity time and the advance time fr for furrows Recession can usually be neglected in furrow irrigation if the design computations are being made manually For borders the cutoff time 15 either of two conditions 1 when the difference between the recession time 7 and the advance time amp equals the required intake opportunity time Treg for the case where the field control point is at downstream end of the field or 2 when the recession time at the field inlet or depletion time t equals the required intake opportunity time in the case where the field control point is at the field inlet There are volume balance procedures for accomplishing the free drai
132. lted tailwater This field has a grass surface which 15 described by a Manning n value of 0 18 during both initial and later irrigations 8 4 FreeDrainingBorder 4 The FreeDrainingBorder 4 data describe a 24 7 acre field irrigated by canal water supply having a maximum flow rate of 6 cfs and a maximum availability of 48 hours The soil intake characteristics were selected on the basis of NRCS curve 0 50 which has an average 6 hour intake rate of 0 5 in hr Based on the simulation of this field using the NRCS 0 50 intake curve a unit flow of 0 036 cfs ft applied for 4 hours the application efficiency of this system would be about 39 due primarily to a loss of almost 44 of the inflow to tailwater 10 leaching requirement was more than satisfied with the nearly 17 of deep percolation 8 5 BlockedEndBorder cfg This data set describes a border irrigated field of 33 acres having 1 200 foot dimensions It has a relatively steep slope of 0 00264 but also relatively rough surface indicated by a Manning n of 0 24 for initial and later irrigations due to a crop like alfalfa growing in the border The six hour intake rate for this soil 1s 0 55 in hr The target application depth 1s 3 inches and with the intake coefficients given will require an intake opportunity time of about 312 minutes for initial irrigations and 441 minutes for later irrigations With a unit flow of 0 025 cfs ft the field irrigates with an application effic
133. ltrometer intake family intake rate see chemigation A narrow strip at the head of an irrigated field which is constructed slightly below field elevation used to redistribute water flowing from a pipe or ditch before flowing over the field The dry weight soil moisture fraction in the root zone when vertical drainage has effectively ceased following irrigation or heavy rainfall Generally field capacity 1s assumed to occur at a negative one third atmosphere or one bar of soil moisture tension The dimension of the irrigated field the direction of water flow Usual units are feet The volume of water passing a point per unit time per unit width q or per furrow Another term for flow rate 1s discharge also unit discharge surface irrigation flow rate 1s typically expressed units of cfs or gpm An alternative expression for surface irrigation The practice of surface irrigation using small individually regulated field channels called furrows creases corrugations or rills Portable pipe with small individually regulated gates installed along one side for distributing irrigation water onto a field Acronym for gallons per minute See also cfs unit discharge A small channel along one part of a field that 1s used for distributing water in surface irrigation The process of water movement into and through soil The time dependent rate of water movement into an irrigated soil Usual units are in
134. ly as illustrated Figure IV 16 Unlike small ditch gates the large gates are almost always rectangular in shape Table IV 3 gives the sizing of check outlets and large ditch gates TABLE IV 3 MINIMUM RECOMMENDED CHECK OUTLET AND LARGE DITCH GATE SIZES FOR SURFACE IRRIGATION SYSTEMS Flow cis 26 28 30 35 40 45 so 60 70 80 90 100 120 160 18 0 20 0 25 0 J NN DNE gt 222 wan 1 foot 2 feet 3 feet 4feet IV 4 2 Gated Pipe Design Gated pipe 15 generally used for furrow irrigation although in some cases it has been used for border and basin systems Usually borders and basins require larger flows than would normally be available through gated pipe systems Gated pipe is available in aluminum rigid plastic polyvinyl and lay flat po
135. lypipe from various manufacturers Aluminum pipe 15 available 5 inch 6 inch 8 inch 10 inch and 12 inch diameters Polyvinyl gate pipe 15 usually available in 6 inch 8 inch 10 inch and 12 inch Lay flat is available in the same sizes as well as 9 inch 15 inch 16 inch 18 inch and 22 inch 103 The design of gated pipe involves three steps 1 choosing a pipe material 2 selection and location of the gated outlets and 3 the selection of the pipe size IV 4 2 1 Choosing a Pipe Material In selecting a particular type of irrigation gated pipe irrigators must balance their needs against the cost availability operation and maintenance of aluminum rigid plastic and lay flat pipe Aluminum gated irrigation pipe has been used the longest for furrow irrigation It 1s the most expensive gated pipe but one that has the longest useful life 10 15 years when proper maintenance 15 applied Aluminum gated pipe typically costs about 50 more than polyvinyl and three times as much as the lay flat gated pipe It 1s easy to move and install and since it 1s supplied in 20 30 or 40 foot lengths it is easy to store and clean One of the disadvantages of aluminum gated pipe aside from its high initial cost 1s the leakage from the pipe joints when maintenance is not adequate Once the gates are installed the flexibility of alternative furrow spacing 15 reduced as well The sizes of aluminum pipe are somewhat restricted with the most generally
136. m the field design the unit or furrow discharges are known along with the total flow available to the field The water supply to the field should also be characterized by its energy or head at the field inlet This information may need to be developed from the elevation of the water source if coming from a canal or ditch or from the pressure in the main supply pipeline if otherwise If the field cannot be irrigated a single set its subdivisions should also be known This information will establish the length of gated pipe segments Finally the field topography should yield the slope along which the gated pipe will be laid For purposes of design the discharge in the gated pipe will be assumed to be the total field supply flow even though where the outlets are opens the flow diminishes along the pipe This assumption is made to insure an adequate pipe diameter in the reaches which are simply conveying water to the irrigating location The hydraulics of the pipe are thus described by the Bernouli equation H inlet h L 100 EL EL inlet IV 10 in which Hinet the total head pressure plus velocity at the inlet end of the gated pipe in feet 105 the minimum head at the end of the pipe necessary to deliver the design unit flow feet length of the gated pipe in feet elevation of the end of the gated pipe feet elevation of the pipe inlet feet and the friction gradient in the pipe
137. made within the design panel as shown in Figure 14 Computations now need to be repeated for the later irrigation conditions After a few simulations it be suggested that the target depth be decreased to 3 inches the time of cutoff be increased to 30 hours 1 800 mn the furrow stream reduced to about 4 5 gpm This will result in a tailwater loss of about 123 per furrow and the field can be irrigated in two sets with the 10 cfs available Following the same process as before the number of furrows that can be supplied by the tailwater reuse system 1s 98 The reservoir volume would only need to be about 3 25 ac ft for this condition as opposed to about 2 9 ac ft for the initial irrigations IV 3 5 Design of Surge Flow Systems A rational design procedure for surge flow systems has not been developed and thus 1s not included in the design features of the SURFACE software This does not mean that design 15 not possible The simulation capabilities of the software can simulate any surge flow configuration and through a trial and error process a design can be derived that 1s efficient and effective Inflow Controls Field Topography Geometry Infiltration Characteristics Hydrograph Inputs Design Panel input Data for Design Design Parameters Total Flow LARGEST Total Available Flow 6 1 cfs ES EN Imi Total Total Time Flow is Avaliable irigation 720 Ars Timo hr 96 0 Unit 0 034 fax Ver
138. ment irrigation efficiency At the field level irrigation efficiency 1s the ratio of the average depth or volume of irrigation water stored in the root zone plus the depth or volume of deep percolation that 1s needed for leaching to the average depth or volume of irrigation water applied Inefficiencies are caused by failwater and deep percolation losses above the leaching requirement storage or requirement efficiency Ratio of the amount of water stored in the root zone during irrigation to the amount of water needed to fill the root zone to field capacity Inefficiencies are caused by under irrigating part of the field irrigation interval interval between irrigation events Usual units are days irrigation requirement Quantity of water exclusive of effective precipitation that is required for crop demands including evapotranspiration leaching as well as special needs such as seed bed preparation germination cooling or frosts protection Where there is an upward flow from a shallow groundwater it should reduce the amount of water required from the irrigation system The irrigation requirement is often called the net irrigation requirement Recognizing that no irrigation system can exactly supply the irrigation requirement due to inefficiencies a gross irrigation requirement is often estimated by dividing the irrigation requirement by an irrigation efficiency term Usual units are inches irrigatio
139. moothing of the furrow surface thus increasing wetted perimeter Also with less flow along the furrow the flow cross section 15 less eroded and therefore less efficient The result 1s that wetted perimeter remains nearly constant over substantial length of furrow in spite of discharge reduction This assumption was made in nearly all early versions of surface irrigation models Report after report shows this to be adequate Another important issue in this regard is the spatial variability of infiltration and roughness A number of studies have shown that measurements of roughness a and F will exhibit a great deal of variation over a field The analysis above assumes the values input will be representative of nearly average values for the field Thus while attempts have been made to adjust infiltration and roughness for the effects noted above there are no provisions for spatial variation IV Redesigning Surface Irrigation Systems The vast majority of design efforts the surface irrigation arena will be devoted to modifying or fine tuning systems already in place rather than the development of entirely new systems Perhaps a more descriptive term would be redesign One can readily see different design objectives in the two views of surface irrigation design The focus of new system design 1s to create a workable profitable and effective system The focus of redesign or design modification 1s conservation of water l
140. more of these pipes however The individual gated pipes are now only 390 feet long The friction gradient for this case 15 6 0 0 0001 x 390 0 6 h m 1 375 fi 100 fi 390 100 From Table IV 4 this would probably require only a 12 inch pipe and therefore could be lay flat aluminum or polyvinyl However the irrigator and designer might consider it unlikely that the savings in gated pipe cost would compensate for the additional buried mainline m BEBE EE 7 e Control Valve Inlet Valve Buried Mainline Gated Pipe Run Length 591 Run Width ft 262 Figure IV 20 Alternative gated pipe layout for FreeDrainingFurrow 1 IV 4 3 Comparing Alternatives for Headland Facilities This section 15 not meant to be a comprehensive treatment of headland facility design but to illustrate some basic principles methodologies Keeping in mind that most work to modernize or improve surface irrigation systems will occur within existing systems a workable if perhaps suboptimal solution will present itself upon initial inspection Specifically one indication of what should be done to improve the function and efficiency of headland facilities 15 to improve what already exists There are no reliable criteria that would allow a designer to determine the best head ditch or pipe with their various offtake options without a site assessment One only need visit an irrigated area to find many c
141. mparing the net crop demands with the capability of the water delivery system to supply water according to a variable schedule can produce a tentative schedule Whichever criterion crop demand or water availability governs the operating policy at the farm level the information provided at this stage will define the limitations of the timing and depth of irrigations during the growing season The type of surface irrigation system selected for the farm should be carefully planned Furrow systems are favored conditions of relatively high bi directional slope row crops and small farm flows and applications Border and basin systems are favored in the flatter lands large field discharges and larger depths of application great deal of management can be applied where flexibility frequency and depth are possible IV 2 2 Detailed Design The detailed design process involves determining the slope of the field the furrow border or basin inflow discharge and duration the location and sizing of headland structures and miscellaneous facilities and the provision of surface drainage facilities either to collect tailwater for reuse or for disposal Land leveling can easily be the most expensive on farm improvement made in preparation for irrigation It 1s a prerequisite for the best performance of the surface system Generally the best land leveling strategy 1s to do as little as possible 1 e to grade the field to a slope that involves mini
142. ms should have a high flow capacity and therefore the outlets are generally slide gates or checks The smaller ditch gates siphons and even gated pipe should not be ruled out where the soils have low intake rates and or the fields have relatively high slopes Furrow irrigation systems on the other hand work best when flows to individual furrows be regulated This can be accomplished by siphon tubes spiles or ditch gates from a head ditch or by gated pipe Since the gated pipe outlets are more easily regulated than siphons spiles or ditch gates many irrigators engaged in improving their systems performance choose gated pipe Another important factor 1s the flexibility to accommodate changes in cropping patterns The crop rotations of some farming units involve border irrigation for some crops and furrow irrigation for others A head ditch with ditch gates works well both circumstances but gated pipe might be equally effective particularly if intake rates are low Finally labor is rapidly becoming the farm s most critical shortage and any surface irrigation system modernization and improvement program must reduce the labor required to operate it effectively if efficiency 15 to be increased Automation 15 the ultimate labor saving technology Thus all things being equal the best headland facilities might be those that can be automated However the headland facilities are selected they must be capable of delivering the proper unit fl
143. mum earth movement Exceptions occur where other considerations dictate a change in the type of system say basin irrigation and yield sufficient benefits to offset the added cost of land leveling If the field has a general slope in two directions land leveling for a furrow irrigation system 1s usually based on a best fit plane through the field elevations This minimizes earth movement over the entire field and unless the slopes in the direction normal to the expected water flow are very large terracing and benching would not be necessary A border must have a zero slope normal to the field water flow and thus will require terracing in all cases of cross slope Thus the border slope 15 usually the best fit sub plane or strip Basins of course are level 1 no slope in either direction Thus terracing 15 required both directions When the basin 1s rectangular its largest dimension should run along the field s smallest natural slope in order to minimize leveling costs Field length becomes a design variable at this stage and again there 1s a philosophy the designer must consider In mechanized farming long rectangular fields are preferable to short square ones This notion 15 based on the time required for implement turning and realignment The next step in detailed design 1s to reconcile the flows and times with the total flow and its duration allocated to the field from the water supply On small fields the total supply may provide
144. n 17 Furrow systems can also be served by field bays or narrow shallow channels at the head of the field that create a small reservoir from which individual furrows are supplied water Figure 1 4 presented earlier showed an example of this furrow irrigation configuration In this case water 1s diverted from a head ditch into the field bay and then diverted into the furrows with siphons 1 3 6 Cutback In order to achieve the most uniform surface irrigation the advance phase has to occur fairly quickly and to do so requires a relatively large unit flow In border or basin irrigation the inflow is terminated in most cases before the advancing front reaches the end of the field In furrow irrigation however it 15 nearly always necessary to maintain inflow well beyond the completion of advance in order to refill the root zone Consequently the runoff or tailwater volume can be high and the efficiency low One way of overcoming this problem 15 to allow a high flow during the advance phase and then reduce it to a smaller value during the wetting phase and thereby minimize tailwater This is called cutback A simple example is the use of two siphons per furrow during the advance phase and then reducing the flow by eliminating one of the siphons during the wetting phase Furrow irrigation automation has not been very successful until the advent of the surge flow concept although systems like Cablegation system developed in Idaho
145. n set A subdivision of the field that is individually irrigated Sets are generally required whenever the supply flow is too small to irrigate the entire field at once land leveling A general reference to the process of shaping the land surface for better movement of water A more correct term is land grading When land grading is undertaken to make the field surface level the term land leveling can be used as a Specific reference Related terms are land forming land smoothing and land shaping leaching The process of transporting soluble materials from the root zone the deep percolation The most common of these materials are salts nutrients pesticides herbicides and related contaminants leaching fraction LF Ratio of the depth of deep percolation required to maintain a salt balance in the root zone to the depth of infiltration Also referred to as the leaching requirement xili An abbreviation for management allowable depletion maximum allowable deficiency 15 the soil moisture at which irrigations should be scheduled In the evaluation or design of surface irrigation systems MAD 15 referenced as a required depth per unit length or a volume per unit length per unit width or furrow spacing Zreq opportunity time Treg The cumulative time between recession and advance at a specific point on the surface irrigated field Usual units are minutes or hours permanent wilting poin
146. n the quality of the water throughout the root zone Salinity is usually the most important quality parameter in surface irrigation and the higher the salinity in the irrigation water the higher will be the concentration of salts in the lower regions of the root zone However since basins do not apply water to the crop canopy as does sprinkle irrigation water supplies with relatively high salinities can be used Some water supplies also have poor quality due to toxic elements like Boron The most important factor in achieving high basin irrigation uniformity and efficiency while minimizing operational costs 1s the discharge applied to the field In basin irrigation the higher the available discharge the better constrained only by having such a high flow that erosion occurs near the outlet The duration of irrigation 1s dependent on the depth to be applied the flow rate onto the field and the efficiency of the irrigation Basin irrigation s typically high discharges and high efficiencies mean that basin irrigations may require less total time than borders and furrows This coupled with the fact that basins usually irrigate heavier soils and apply larger depths means that the irrigation of basin 15 typically less frequent than borders or furrows The duration and frequency of basin irrigation impose different requirements on the water supply system than systems operated to service border and furrow systems 1 2 1 5 Climate Whenever water ponds
147. ncreasing the bottom width to 30 inches would yield a depth Top Width ft 7 6787 of just over 2 feet The maximum depth in the ditch should not wetted Perimeter ft 3 2533 exceed 90 of the depth or 2 7 feet 99 Border Basin Siphons Border Basin Check Outlet Border Basin Gate Figure IV 16 Typical surface irrigation head ditch configurations 100 This ditch 1s somewhat large due to the relatively flat cross slope of the field It be useful to construct the ditch on a steeper grade by elevating the inlet IV 4 1 1 Sizing Siphon Tubes and Spiles Siphon tubes and spiles act as simple orfices For the purpose of design minor losses at their entrance and friction losses are assumed to be negligible The design of these devices involves choosing a diameter that will accommodate the necessary flow There are two conditions that typically exist the operation of the siphons and spiles The first 15 when the downstream end of the siphon or spile 1s submerged by the water level the field as shown in Fig IV 17b The second condition occurs when the downstream end discharges freely into the air as shown in Figs IV 17a and IV 17c The head on these structures should be the typical difference between the operational level of the head ditch and either the field water level or the center line of the freely discharging spile or siphon Table IV 1 provides guidelines for selecting siphon and spile diameters as a function o
148. nd recession and subsequent advance without problems but the numerical failures are common enough that the software has been programmed to discontinue simulation for all case of front end recession during cutback 4 3 3 Leaching Fraction Although the software does not simulate or evaluate Leaching Fraction 0 10 water quality parameters like salinity the definition of irrigation efficiency includes a leaching fraction term A more detailed discussion of efficiency is given in Section III 4 3 4 Simulation Speed and Graphical Presentation Simulation Speed Modern computers will execute the most intensive of the 4 SURFACE programming too fast for clear run time graphical 4444444 presentation In order to adjust computational speed the software has Graphic Profile Slope built in delays that can be adjusted by moving the Simulation Speed aE track bar to the right faster or left slower The lower track bar will adjust the plotting slope of the run time surface and subsurface profiles This feature has been included solely for presentation purposes and has no computational or physical ramifications 4 4 Hydrograph Inputs Three of the important uses of software such as SURFACE 1 to evaluate the operation of existing surface irrigation systems 2 to simulate the design of a surface irrigation system and 3 to compare the simulated and measured conditions The Hydrograph Inputs panel of the input tabb
149. ne Figure IV 9 Design Panel for the final design of the FreeDrainingBorder 4 initial irrigation example The design for the later intake conditions requires adjustments to the flow and cutoff time By decreasing the flow to 0 01 cfs ft and extending the cutoff time to 10 hours the field can be irrigated three sets achieving an application efficiency of 57 Although this irrigation example has been substantially improved the performance is relatively poor and demonstrates two inherent problems with free draining borders First there can be as much as 5 times the amount of water on the field surface at the cutoff time as a furrow system and therefore tailwater can be a major problem Secondly if a substantial leaching requirement 15 needed high tailwater losses are unavoidable The best performing borders like basins are those with blocked ends as will be demonstrated below The designer must now address the issue of whether or not the field has to accommodate the full 6 cfs during each irrigation or whether it can be operated with a flexible supply flow For the first irrigations the field would need to irrigate with six sets each having a reduced flow of about 0 027 cfs ft The irrigation efficiency would decrease to 69 indicating that the efficiency cost would be about 4 due to fixing the field supply rate Later irrigations would remain the same IV 3 2 Blocked end Surface Irrigation Design Blocking the end of basin b
150. ng initially that intake could be represented by the function 1 in which z is cumulative intake in inches 15 intake opportunity time in minutes and and are empirical constants The definition of basic intake rate 75 in inches per hour was then 2 abs 0 10 A 2 This relationship occurs when 600 a 1 A 3 The basic intake rate thus defined was extracted from the ring infiltrometer data and grouped into 10 layers represented by averages of all the tests within the layer The time to infiltrate 1 2 3 4 and 6 inches were interpolated from each of the 5 reading averages and then averaged over the layer as shown in Table A 1 Then the Philip equation was used to fit the data in Table A 1 The expression of the Philip equation 15 z Sv A 4 in which S is the soil sorptivity and A is the soil transmissivity and the resulting fit with the layer ring data produced the following relations Philip 1957 The Theory of Infiltration 4 Sorptivity and the Initial Moisture Content and 5 Influence of the Initial Moisture Content Soil Science 84 257 337 111 TABLE 1 LAYERED SCS RING INFILTROMETER DATA Average Range of J No of Test Ip in hr Groups in hr Under 0 1 021040 0 29 49 73 180 onon 49 405 23 66 onis 102 0 648 18 U6 33 126 1
151. ning design process and they work reasonably well for furrow irrigation They can be used for free draining borders but the recession computations are inaccurate Consequently it is not recommended that volume balance be used in design but rather the hydrodynamic features of the NRCS SURFACE software or a similar program such as SRFR 9 Simulated System Performance software Advance Time min 405 3 Application Efficiency 75 47 51 Requir e mt Efficiency Yo 99 29 IV 5 1 1 Example Free Draining FurrowDesign Open an instance of SURFACE load the FreeDrainingFurrow l cfg data file supplied with the Irrigation Efficiency 52 62 software and execute the simulation programming Distribution Uniformity 93 75 for the initial intake condition At the end of the Dist Efficiency 4 47 94 dT simulation observe the distribution of infiltrated water and runoff as well as the various efficiencies and uniformity that were determined Then click on the plot output Tailwater Fraction 0 89 Deep Perc Fraction 51 60 Strelkoff T S Clemmens A J and Schmidt B V 1998 SRFR v 3 31 Computer Program for Simulating Flow in Surface Irrigation Furrows Basins Borders U S Water Conservation Lab USDA ARS 4331 E Broadway Phoenix AZ 85040 82 results Be and from the drop down menu Current Data Plot Options select Advance Data and then Tailwater Data These two plots are reproduce
152. ntake parameters using the volume balance procedure click first on the Infiltration Characteristics panel and set the Qinfilt box to 0 033 cfs Make sure the Continuous Inflow Hydrograph radio button in the Input Control is selected and that the Two Part parameters in the boxes below the are set to 352 7 minutes 116 minutes and 1013 feet respectively Then click the button and notice that the a and parameters are adjusted to 0 2473 and 0 01859 respectively Repeat the simulation using these data by clicking on the button Finally activate the advance recession and tailwater runoff hydrograph plots as presented below in Figs 13 and 14 73 Elapeed se 2 E ae ee AAA m S x E e X e E mH e PEN M i 1 rs no pu po pa a go uy 8 pou ooo u quu P uu EUF ruu 1008 7100 1200 1100 71400 1600 zuuu z199 alang fari Figure 11 Advance recession curve for the example FreeDrainingFurrow_2 cfg data Runo Rate UU us m o 1 E Lapsed Tire Is Figure III 12 Tailwater hydrograph for the example FreeDrainingFurrow 2 cfg data 74 Blapeud Tiro Days LX NN CN PX KM m A KM m X X NUNC X K OMM es NUR m ce X m a m e m RP aur 340 2 00 9 cdi 0 100 300
153. o illustrate the problem of irrigating a long Advance Time min 248 furrow in a relatively high intake soil This is also one of the Application Efficiency 68 18 conditions that surge flow was originally thought to offer X Bequire mt Efficiency 99 04 Irrigation Efficiency 74 61 some advantage If this file 15 loaded into the SURFACE ytriirtinn Uniformity 84 19 software it can be modified to simulate various surge flow Dist Efficiency 81 10 options For purposes of example the Inflow Regime in the Tailwater Fraction 15 94 Inflow Control panel of the input tabbed notebook can be Deep Perc Fraction 15 59 changed to a surge flow regime by checking on the box labeled Fixed Cycle Surge Flow Then under the headings of Run Parameters the number of surges can be set to a number like 7 and the surge cycle on time to a value like 40 minutes For the purposes of this demonstration the furrow stream has left at 32 gpm but the target depth of application reduced to 3 inches Also the time step Dtm should be reduced to 0 5 minutes Figure IV 15 shows the resulting advance recession plot performance of the system is shown at the right The implementation of surge flow in this case increased the application efficiency by 14 since the nearly 52 deep percolation loss and 1 tailwater loss under continuous flow became a 15 deep percolation loss and a 24 tailwater loss under the surge flow reg
154. o open the input tabbed notebook with the software s default data set as shown in Fig 9 below Inflow Controls Field Topography Geometry Infiltration Characteristics Hydrograph Inputs Design Panel 1181 1 Flow Cross Section ba ield Length Top Width 14 173 Field Width ft 656 2 Field 5 0 00000 Middle Width in 11 024 asin Unit Bottom Width i 3937 Width ft or Row SET j 5 pacing ft Field System Maximum linj 4 724 Border Basin Irrigation F Furrow Irrigation Downstream Boundary Free Draining Manning n Values First Irrigations 0 040 Later 0 030 Compound Slopes First Slope 0 00800 Manning Equation Calculator Second Slope 0 00800 Slope 0 00000 Rho Third Slope 0 00500 Manning 0 0000 Sigmal First Distance ft 1181 1 Flow gpm 0 0000 Sigma Second Distance ft 1181 1 Depth ft 0 0000 Gammal The First Distance is the distance Area ft 0 0000 Gammaz from field inlet to the break in slope Cmh between First Slope and Second Top Width ft 0 0000 E LT E Es LT Wetted Perimeter ft 0 0000 Figure III 9 Example cross section evaluation using the SURFA software Make sure the field system 15 furrow irrigation by noting the checked Furrows radio button Then enter 15 0 inches for the Top Width 12 inches for the Middle Width 2 inches fo
155. oderate to heavy texture soils textured soils textured soils Solid stand crops Solid stand crops Water Supply Low discharge long Moderately high High discharge short duration frequent discharge short duration infrequent supply duration infrequent supply supply rainfall to moderate rainfall Efficiency and Relatively low High with blocked High Uniformity ends L3 WATER MANAGEMENT IN SURFACE IRRIGATION SYSTEMS Surface irrigation is difficult to manage at consistently high levels of performance efficiency and uniformity because the basic field characteristics change from irrigation to irrigation crop to crop and year to year For example the soil intake changes dramatically between the first irrigation following cultivation and the next The field 1s also smoother so long as the crops do not grow in the flow path but will become rougher as the season progresses 12 when they do These variations cause the water to not only infiltrate at different rates but also change how fast the water advances over the field and recedes from it after the flow 1s turned off If an irrigator misjudges the behavior of the system the performance will decline It is not surprising that surface irrigation efficiencies worldwide are low At the appraisal design or rehabilitation stage the essential questions to be asked about the surface irrigation system are what kind of surface system should be selected what unit flows to choose when to t
156. of the Interior as its water measurement guide Section 15 Chapter 9 National Engineering Handbook This manual is also available from your state irrigation specialist or IT personnel or can be downloaded directly from http www usbr gov pmts hydraulics_lab pubs index html FIELD EVALUATIONS III 3 1 Standard Field Evaluation Procedure The basic objective of a surface irrigation field evaluation 1s to establish a water balance for the field and thereby identify each of the components necessary to determine the efficiencies and uniformities noted Eqs III 20 through III 25 Standard practices are developed other NRCS manuals and will not repeated here detail However based on recent experience a number of simplifications and modifications can be suggested III 5 1 1 Flow Shape In order to estimate flow depths it 1s necessary to describe the shape of the flow cross section For borders and basins this shape 1s generally assumed to be a wide rectangular sheet which can be evaluated by examining a unit width within the border or basin In furrow irrigation however it 1s necessary to describe the actual shape so that relationships between depth and area and or wetted perimeter can be calculated Furrow shapes are nearly always irregular but can be described using a series of power functions The following analysis uses the Manning equation as the primary relationship between depth slope cross section and flow
157. ombinations of headland facilities doing essentially the same tasks 109 but doing so manner that suits the irrigator best Historically selecting irrigation facilities has been primarily concerned with the cost side of cost effectiveness However with the goal of modernization mind and anticipating that effectiveness will become increasingly important irrigation efficiency will be substantially more important in the future Perhaps one of the most important features of surface irrigation systems of the future will be the capability to precisely regulate the unit flows onto the field This requires that the total flow to the field be known accurately and that the unit flows can be achieved precisely Earlier sections of this chapter have demonstrated that when the proper flow 1s added to a border basin or furrow high uniformities and efficiencies will result This suggests that adjustable gates are better selections than checks spiles or siphons Seepage and leakage losses from the headland facilities should be minimized which suggests lined head ditches or pipelines One of the most important factors in choosing a particular type of headland facility a head ditch or pipe for instance 1s the type of surface irrigation system being serviced As a rule pipes that carry the flow necessary for border or basin irrigation are far more expensive than lined or unlined ditches Outlets from head ditches for border and basin irrigation syste
158. omorrow most of what 1s carried brief case will be carried in a shirt pocket And perhaps a new generation of biosensors will be available that will allow surface irrigation systems to be managed on line and real time In recognizing the need to update Section 15 the NRCS also recognized the need to provide modern tools for simulating evaluating and designing surface irrigation systems The NRCS SURFACE program was written to fulfill this need SURFACE 1s a comprehensive software package for simulating the hydraulics of surface irrigation systems at the field level selecting a combination of sizing and operational parameters that maximize performance and a convenient way to merge field data with the simulation and design components The programming uses 32 bit C language to encapsulate the numerical procedures which describe the hydrodynamic theory in general use today The software has been written for compatible micro or personal computer systems utilizing Microsoft Corporation s Windows 95 or later operating systems This section provides the reader with a user s manual for the SURFACE program and some detailed data sets that demonstrate its use 2 GETTING STARTED SURFACE and its companion files can be obtained from your state irrigation specialist or IT personnel The local IT person can provide help installing the program There are a number of files included in the package These include the NRCS SUR
159. oocoocao Sandy 027951 0020930 TABLE 8 CONTINUOUS FLOW BORDER BASIN INTAKE FAMILIES LATER IRRIGATIONS Continuous Flow Intake Curve Parameterz for Later Irrigations ID Soil a k fo Heavy Clay Clay Clay Light Clay Clay Loam Clay Loam Clay Loan Silty Silty Silty Loam Silty Loam Silty Loam Silty Loam Sandy Loam Sandy Loam Sandy Loam Sandy Sandy Sandy Etran 005640 009476 012843 014820 016136 017117 017860 018446 018923 019331 019660 020210 020641 020982 021274 021526 022330 022826 023761 exe 0001713 0003965 0005981 0007516 0008779 0009843 0010736 0011508 0012195 0012797 0013324 0014245 0014976 0015588 0016086 0016508 0017718 0018069 0016748 58 TABLE 9 SURGE FLOW BORDER BASIN INTAKE FAMILIES INITIAL Surge Flow Intake Curve Parameterz for Initial Irrigations Heavy ID Soil Hame Clay Clay C
160. order or furrow systems provides the designer and operator with the ability to achieve potential application efficiencies comparable with most sprinkle systems While blocked end fields have the potential for achieving high efficiencies they also represent the highest risk to the grower Even a small mistake in the cutoff time can result in substantial crop damage due to the scalding associated with prolonged ponding on the field 88 Consequently all blocked end surface irrigation systems should be designed with emergency facilities to drain excess water from the field Figure IV 10 shows the four stages of typical blocked end irrigation In Fig IV 10a water 15 being added to the field and 15 advancing In Figure IV 10b the inflow has been terminated and depletion has begun at the upstream end of the field while the flow at the downstream end continues to advance This 1s important Typical field practices for blocked end surface irrigation systems generally terminate the inflow before the advance phase has been completed In Figure IV 10c the depletion phase has ended at the upstream end the advance phase has been completed and the residual surface flows are ponding behind the downstream dike Finally in Figure IV 10d the water ponded behind the field dike has infiltrated or been released and the resulting subsurface profile is uniform along the border and equal to the required or target application The dilemma for the designer of a b
161. original SCS intake families eere 114 Vil LIST TABLES TABLE 1 1 A GENERAL COMPARISON OF SURFACE IRRIGATION METHODS M 12 TABLE 1 AVERAGE ROOTING DEPTHS OF SELECTED CROPS IN DEEP WELL DRAINED SOILS 49 TABLE III 2 AVERAGE 6 HOUR INTAKE RATES FOR THE FURROW BASED REFERENCE INTAKE 1 85 1 1 eterne unen eene 54 TABLE 3 CONTINUOUS FLOW FURROW INTAKE FAMILIES INITIAL IRRIGA TIONS T M 55 TABLE 4 CONTINUOUS FLOW FURROW INTAKE FAMILIES LATER IRRIGA TIONS arisen 55 TABLE III 5 SURGE FLOW FURROW INTAKE FAMILIES INITIAL IRRIGA TIONS T 56 TABLE 6 SURGE FLOW FURROW INTAKE FAMILIES LATER IRRIGA TIONS 56 TABLE III 7 CONTINUOUS FLOW BORDER BASIN INTAKE FAMILIES INITIAL IRRIGA LIONS 58 TABLE 8 CONTINUOUS FLOW BORDER BASIN INTAKE FAMILIES LATERAIRRIGATIONS iiec eire 58 TABLE 9 SURGE FLOW BORDER BASIN INTAKE FAMILIES INITIAL IRRIGA TIONS er 59 TABLE 10 SURGE FLOW BORDER BASIN INTAKE FAMILIES LATER IRRIGATIONS 5 59 TABLE IV 1 MINIMUM RECOMMENDED SIPHON AND SPILE SIZES FOR SURFACE IRRIGATION SYSTEMS ecce eee ee eee eene nuu 102 TABLE IV 2 MINIMUM RECOMMENDED DITC
162. ot Depth Crop ft Crop ft Alfalfa 5 Grapes 3 Almonds 7 Ladino clover and grass mix 2 Apricots 7 Lettuce 1 Artichokes 4 5 Melons 5 Asparagus 3 0 Milo 4 Barley 4 Mustard 3 5 Beans dry 3 5 Olives 5 Beans green 3 Onions 1 Beans lima 3 5 Parsnips 3 5 Beets sugar 3 Peaches i Beets table 3 Pears 7 Broccoli 2 Peas 3 Cabbage 2 Peppers 3 Cantaloupes 5 Potatoes Irish 3 Carrots 2 Potatoes sweet 4 5 Cauliflower 2 Prunes 6 Celery 2 Pumpkins 6 Chard 3 Radishes 2 Cherries 4 5 Spinach 2 Citrus 4 5 Squash summer 3 Corn field 4 Strawberries 5 Corn sweet 3 Sudan grass 5 Cotton 4 Tomatoes 3 Cucumber 4 Turnips 3 Eggplant 3 Walnuts 7 Figs 7 Watermelon 5 Grain and Flax 4 The management allowed deficit MAD 15 the soil moisture that can be used by the crop before irrigation should be scheduled For deeply rooted and stress tolerant crops like alfalfa the 49 MAD be as much as 60 65 of TAW whereas for shallow rooted and stress sensitive crops like vegetables the MAD level should not exceed 35 40 of TAW Some crops like cotton and alfalfa seed require a stress period 1n order to produce lint or seeds and MAD may need to be as much as 80 of TAW for some irrigations late the maturation period In the absence of specific information in a locality assuming a MAD level of 50 of TAW can be generally used to schedule irrigations The soil moisture deficit SMD is the depletion of soil moisture at particular soil
163. ow to the field under varying conditions through the season and year to year 110 Appendix A Note on the Development of the Original NRCS Intake Families and Their Modifications for Furrow Irrigation 1 INTRODUCTION In the 1950 s various personnel of the Soil Conservation Service SCS of the USDA began a concerted effort to develop general intake relationships to support surface irrigation assessments when field measurements were not available In the 1950 s 1670 ring infiltrometer tests were made in grass and alfalfa fields of Colorado Wyoming North Dakota South Dakota and Nebraska Most but not all of the tests were conducted within irrigated fields The individual tests were averaged in groups of five for analysis In 1959 J T Phelan proposed the intake families now found the USDA SCS National Engineering Handbook Section 15 Chapters 4 Border Irrigation and 5 Irrigation As the need to revise the NEH to make it current with existing surface irrigation technology emerged in the late 1990 s so too did the need to re examine and revise the intake families A 2 EVOLUTION OF THE ORIGINAL CONCEPT The ring infiltrometer data collected 1n the 1950 s were evaluated in several ways using principally regression One of first concepts explored was that of the basic intake rate which was defined as that rate when the change of the rate per hour was one tenth of its value in inches per hour In assumi
164. p percolation occurs This yields a total intake over the portion of field where deep percolation occurs of 1 226 2 of which 886 ft are captured in the root zone 990 feet 4 3 inches 2 5 ft 12 in ft The total estimated volume of deep percolation is therefore 340 or DPR 340 2502 0 136 or 13 6 The total intake in the last 330 feet of furrow can be calculated similarly and should equal about 140 making the total water stored in the root zone 1 026 140 886 The application efficiency from Eq III 21 1s therefore 1 026 2502 0 410 or 41 0 The sum of application efficiency tailwater ratio TWR and the deep percolation ratio DPR should total to 10096 In this case the total 1s 100 If the root zone had been completely refilled the volume there would have been 1 183 ft 4 3 inches 1320 ft 2 5 ft Since only 1 026 ft was stored the storage or requirement efficiency from Eq III 22 is 1 026 1 183 0 8756 or 87 6 The distribution uniformity DU can now be found from Eq III 23 as 4 140 1366 0 410 or 411095 This 15 a very poor irrigation would be a candidate for much better management and or design However some improvement in the numbers at least 15 possible by including the leaching the evaluation An approximate volume of leaching can be found by assuming leaching occurs wherever deep percolation occurs in this case over the first 990 feet of the furrow The volume
165. phase tailwater see runoff tailwater reuse system An appurtenance for surface irrigation systems where there 15 tailwater runoff The tailwater 1s first captured a small reservoir and then diverted or pumped back to the irrigation system 1 e either to the same field or to anther in proximity uniformity Irrigation uniformity 15 a qualitative measure of how evenly water 15 applied by the surface irrigation system distribution uniformity DU surface irrigation the distribution uniformity 15 the ratio of the depth or volume infiltrated in the least irrigated quarter sometimes called the low quarter of the field to the average depth or volume infiltrated in the entire field unit discharge The discharge or flow rate of water applied to an irrigated field per unit width or per furrow Typical units are cfs and gpm wetted perimeter Length of the wetted contact per unit width between irrigation water and the furrow border or basin surface measured at right angles to the direction of flow Usual units are inches or feet wetting or ponding phase The period of time in an irrigation event between the completion of advance phase and the cutoff time wild flooding surface irrigation system where water 1s applied to the soil surface without flow controls and without management of flowrate and cutoff time XV 1 The Practice of Surface Irrigation LI INTRODUCTION surface irrigation 15 the oldest and most common method of
166. phase This value is specified in the Simulated Unit Inflow box Note that this flow is discharge into each furrow or into each unit width of border or basin Occasionally during efforts to evaluate surface irrigation systems an inflow hydrograph 15 measured and the user would like to evaluate the effect of inflow variations This option requires the Continuous Inflow Hydrograph check box to be selected and an input hydrograph specified in the Hydrograph Inputs panel in the tabbed notebook Under a surge flow regime there are two cycle options The first 1s a fixed cycle on time surge flow system and the second 15 a variable on cycle time option It 15 assume that the off time equals the on time and thus the actual cycle time 1s double the on time In other words the cycle ratio on time divided by cycle time 1s always 0 50 SURFACE offers two ways to vary the surge to surge cycle on time The first 1s by multiplying the first surge on time by a user specified fraction See the Surge Adj Ratio edit box For example if the first surge on time is 30 minutes and it is desirable to expand surges by 10 each cycle then the Surge Adj Ratio can be set to 1 1 The second way of 33 varying the surge cycle time 15 by adding a fixed amount of time to each surge on time via the Surge Adj Time parameter If one begins with a 60 minute cycle and wishes to expand it by 10 minutes each surge then the Surge Adj Time parameter 15 set to 10 In both
167. r the Bottom Width and 4 inches for the Maximum Depth these numbers are entered the 67 metric values are displayed in the boxes below labeled Rhol Cch and will change as Eqs 31 to 32 and Eqs 35 to 40 are executed by the software suppose this furrow had a slope of 0 0001 a Manning Equation Calculator Manning of 0 025 and was conveying a flow of 17 gpm What would the depth wetted perimeter and cross slope 0 00010 sectional area be The answer can be found by entering the Manning n 0 0250 slope Manning n and flow in the Manning Equation Flow gpm 17 0000 Calculator as shown here What would the flow depth be Depth ft if the system was a border of the same slope This can icki 0 2113 determined by clicking on the Border Basin check box and re entering slope Manning n or flow The result Top Width ft 1 0550 will be 0 094 feet Wetted Perimeter ft 1 2763 1 3 1 3 Advance and Recession Most general evaluation procedures recommend that advance and recession be measured at several points along the field However these data do not provide sufficient information to justify the added labor associated with the evaluation and certainly not the problems associated with trafficking within the field The readings that are most important are those shown in the advance recession graph in Fig III 10 namely 1 the start time 2 time of advance to the field
168. r Number of Surges or when the downstream end of the field has received a depth of water approximately equal to Zreq As a numerical safety measure the Time of Cutoff will always terminate the simulated inflow even when the check box By Target Application zreq 15 checked Thus to let inflow control to be managed by z 4 the cutoff time must be entered as a large value Likewise the number of surges specified for surged systems dominates the applied depth control and should be set to a large number If controls the shutoff time the control value is the same as specified in the Infiltration Characteristics panel The simulation portions of the models also require a time step which is designated as Dtm The software always computes a default value which can be overridden with an input value particularly if the Din mn 2 10 software 15 encountering convergence or stability problems in the numerical procedure The discharge the program will use in the simulation 1s specified by the user s entry into the Simulated Unit Inflow box 4 3 2 Inflow Regime Simulated Unit Inflow gpm 31 701 The SURFACE software will simulate both continuous and surge flow irrigation There are three continuous and four surge flow regimes as shown in Fig 9 The user may select one regime at a time by clicking on the respective check box Generally surface irrigation systems are designed with a fixed inflow during the advance
169. r reservoir and pump back system is shown in Fig I 9 Figure I 9 A typical tailwater recovery and reuse system 1 3 5 Automation and Equipment High labor requirements are a disadvantage of surface irrigation that many irrigators cite as reasons for converting to sprinkle or drip irrigation Automation which can regulate the supply flow to various parts of the field and properly adjust unit flows and cutoff times 15 a critical need in surface irrigation Unfortunately experience to date has been mixed because a standard technology has not been developed for widespread use 1 3 5 1 Border and Basin Facilities and Automation some of the common facilities for border and basin irrigation are shown in Fig I 10 They include single gate offtakes ditch gates siphons alfalfa valves and simple check dividers to show a few options The automation for basin and border involves mechanizing and controlling individual outlets and 15 comparatively straight forward for the single gate offtakes For instance the jack gate shown in Fig 1 10 can readily be equipped with a remotely controlled actuator such as a pneumatic piston Where water control involves siphons or ditch gates automation 15 generally impractical As a rule automation of border and basin offtakes involves retrofitting mechanization to the gate and then connecting it via wire telephone or radio to a controller where the irrigator can make remote changes or where regulation can be m
170. r the cases the user wishes to simulate evaluate or design by having checked the boxes next to the Simulate label Specifically looking at the figure below 1f the user 15 interested in only simulating initial continuous flow then the values necessary are just in that column If surge flow is to be evaluated the intake coefficients Tables Tables Tables Tables are necessary in the first and third columns By changing the check box selections the user can simulate later irrigation conditions as well The surge flow check boxes are deactivated since it 15 necessary for the simulation of an initial surge flow or later surge flow condition that the associated continuous flow intake be used for the flow of water over the dry portion of the field The SURFACE software includes sets of values for k fo and or a Fy and which can be accessed by clicking on one of the buttons The intake functions represented are based on the original USDA SCS intake families modified to be consistent with 30 for the intake equations used in the SURFACE software See Section 2 2 Figure 8 show one of these tables for a furrow system set of values can be selected by clicking on the associated radio button on the left of the table The corresponding values will then be automatically entered the boxes of Figure II 7 The c or values terms to adjust for large field cracks and may set to zero The
171. rder Basin Infiltration and Furrow 114 1 LIST OF FIGURES Figure I 1 Layout and function of irrigation system components ee 1 Figure 1 2 The basic phases of a surface irrigation event 2 Figure 1 3 Typical basin irrigation system in the western 17 5 3 Figure 1 4 Furow irrigation using siphon tubes from a field bay 6 Figure I 5 Contour furrow irrigation ccccccccccsssssssssssssssssssssssscccccccccssssscssssssssssssssssssscecs 7 Figure I 6 Border irrigation in 8 1 eene eee e eee eee e tease eee 9 Figure 1 7 Illustration of contour border irrigation ccce eee e creen eene 9 Figure 1 8 Tailwater outlet for a blocked end border system 11 Figure 1 9 A typical tailwater recovery and reuse system cc eecc eee e eee eene 15 Figure 1 10 Typical border and basin field outlets 16 Figure I 11 A wheel lift slide gate before and after automation 16 Figure I 12 Two methods of supplying water to furrows ecce eere eene 17 Figure 1 13 Gate pipe options for furrow irrigation eee eee e eere eene nne 17 Figure 1 14 Schematic Cablegation system
172. recession plot from the SURFACE graphics output 37 Figure II 12 A typical runoff hydrograph from the SURFACE graphic output 37 Figure II 13 A typical plot of intake distribution for the SURFACE graphics output 38 Figure 14 The main simulation 1 1 38 Figure 15 The SURFACE design panel ccccscssssssssssccccccccccssccccccssssssssssssssscees 39 Figure 1 Components of the soil water matrix eee eee e eere eene nenne 47 Figure 2 Components of soil 48 Figure 3 Variation of available soil moisture with soil type 49 Figure III 4 Average 6 hour intake rate for the revised NRCS furrow intake families PA IIR 54 Figure 5 Reference wetted perimeters for the revised NRCS intake families 57 Figure 6 Reference flow for the NRCS intake families 57 Figure 7 Distribution of applied water in surface irrigation 60 Figure 8 Cross sectional shapes for furrow and border basin irrigation 66 Figure III 9 Example cross section evaluation using the SURFACE software 67 Figure 10 Field measurement points for advance and recession evaluations in the Re
173. rigation the availability of delivery must be more frequent and for longer durations More water on a volumetric basis 1s required for furrow irrigation because of its lower application efficiency in most cases salts can accumulate between furrows and therefore the quality of irrigation water 1s more important in furrow systems than in basins or borders 1 2 2 5 Climate The climate over a surface irrigated field does not have significant impacts on the furrow irrigation Scalding 1s seldom a problem even when the furrow ends are blocked High winds can retard the furrow advance but this 1s rarely a problem The effect of water temperature 1s less furrows than in borders or basins because the wetted area 15 less 1 2 2 6 Cropping Patterns Furrows are ideally suited for row crops of all kinds but are also used 1n solid plantings like alfalfa and grains When the seed bed 1s between furrows and must be wetted it is necessary to apply water to the furrows for extended periods and efficiencies of these emergent irrigations be very low lateral movement of water or subbing wetting across etc is relatively slow process so many irrigators of higher value crops like vegetables use portable sprinkle systems for the emergent irrigations Special crops like rice are generally not irrigated with furrows because of the need for a uniform submergence to control weeds 1 2 2 7 Cultural Factors Most of the cultural
174. s like furrow irrigation Figure I 6 illustrates a typical border irrigation system in operation Fields may have a slope along the traditionally long rectangular fields but cannot have a cross slope The flow covers the entire surface and may be blocked at the downstream end to prevent runoff Borders can also follow the contour lines in terraced fields as shown Fig 1 7 REPERTUS Em E T pa axe PA vua m Fig wa us icy pero in t a emm ird VENE Border irrigation in progress ure I 6 Figure I 7 Illustration of contour border irrigation 1 2 3 1 Development Costs The two major development costs for borders are land leveling and border construction Land leveling 1s more extensive than for furrows and less extensive than for basins particularly if the field 1s leveled along the existing slope in the direction of flow The border dikes do not have to be as high as for basins but do need to be maintained in order to prevent cross flow into adjacent borders and care should be taken to intercept the flow that can occur the dead furrow created by the diking equipment Borders do not generally require as much labor as furrow irrigation but do require more than for basins since the time of cutoff has
175. s the flow per unit width 1s selected properly However as with basins borders are better suited to the heavier soils and crusting soils may require special care such as furrowing 1 2 3 4 Water Supply Typical water applications under border irrigation are similar to basin systems usually larger than furrows In general border systems require 3 5 times as much flow per unit width as furrow systems and somewhat less than basins For example it would not be unusual to irrigate furrows on a spacing of at 2 5 feet with a 15 gpm flow 6 gpm ft and to irrigate a border with the same soil with a flow of 20 gpm ft The same water quality constraints noted for basins apply to borders as well Consequently water supplies for borders should be relatively high discharges for relatively short durations on relatively long intervals 1 2 3 5 Climate Scalding 15 a more serious problem in blocked end borders than in basins because the end depths are greater and require longer to drain from the field It is common practice to provide blocked end borders with surface drainage capability case an error 15 made the time of cutoff and too much water ponds at the end of the field Figure I 8 shows one of these end drains in a border irrigated alfalfa field 10 Figure 8 Tailwater outlet for a blocked end border system In areas of high rainfall ponding and subsequent scalding may be a problem without a surface drainage capability And
176. s velocity dx r pt E V 51 and when the advance has reached the end of the field 71 dt rpt V III 52 i y The value of o at both midpoint and the field length can then be estimated as 0 776 gt 7 222 20 III 53 1 3636 0 776 ar III 54 x 0 5L I 363e s 5L 3 2 2 Volume Balance Estimate of Kostiakov a and Data from field evaluation will have defined and therefore Ao as well as tr fr and therefore r V V and The unknowns in Eq 49 are the intake parameters and F or a k and c if the border basin evaluation is being conducted The value of the cracking term or C must be input separately if it is known Solving for these Eq 49 provides the methodology for evaluating the average infiltration function along the length of a field using basic evaluation data As noted above the procedure for finding intake parameter is iterative The steps are as follows for furrow systems specifically and are the same for border basin systems with the appropriate intake parameters Note that the software accomplished these steps interactively as will be demonstrated below l Assume an initial value of F to be zero Equation III 49 can then be solved for any distance from the field inlet to define the volume balance at any time during the advance phase but perhaps the two most
177. selectable option accessed via the Units menu at the top of the main screen as shown here Units may also be selected from the Infiltration Characteristics File Input Output Simulate Design Pe glish cFs E a English gpm Metric panel in the input tabbed notebook 24 Output Preview File Units B C D Distance in Time of Time of Cummul feet Advance Recession in 1 min in min inches 0 00 6 79384 2 00 6 79499 4 00 B rrr88 5 00 6 79809 8 00 6 76744 10 00 6 75165 12 00 6 73854 CO Foster Alecia Deaths 14 00 6 72359 16 00 6 70173 18 00 6 68284 20 00 6 66273 22 00 6 64327 24 00 6 62111 26 00 6 59866 28 00 6 57552 30 00 5 55238 32 00 6 52865 34 00 6 50303 36 00 6 48325 38 00 6 45952 40 00 6 43514 42 00 6 41046 44 00 6 38556 Figure 4 The SURFACE tabular output screen There are three options two for English and one for a metric system of units The default selection 1s English gpm as shown The selected system of units 1s stored with the input data file so each time the user loads the particular file those units will be displayed and used Thus the unit selection should be made before entering input data and or before saving the input data file 3 5 Simulation The selection of Simulate on the main menu bar or the speed button will cause the simulation programming to execute using whatever data are currently stored in memory A number of sa
178. sh to find the flow that maximizes irrigation or application efficiency while insuring that at least 95 of the field root zone deficit has been replaced by the irrigation 7 1 5 Cutoff Time shutting the flow off when irrigation 15 complete 1s one of the most important operational parameters in surface irrigation and one that 15 often most difficult to determine Many irrigators choose convenient cutoff times also called set times in order to reduce irrigating time or move the delivery from set to set at easily scheduled times 41 As rule designed cutoff times should be an integer fraction of a day and hourly For instance one could have 1 2 3 4 6 8 and 12 hours set times in one day Setting a cutoff time of 252 minutes is unworkable without automation Having said this however under severe water supply constraints many irrigators manage their water on intervals that are highly variable and often at intervals of much less than an hour 7 2 Field Layout On the right side of the design panel the SURFACE software includes a field divider tool Two up down buttons are provided at the top of a rectangular representation of the field Note the width and length scales are not equal so that very pep wide fields still assume the vertical rectangular shape By clicking on the top or bottom button of the vertical up down button the field can be subdivided along its length axis As shown the field length
179. shed by selecting the check box for the later irrigation conditions on Infiltration Characteristics panel input tabbed notebook as shown in Fig IV 6 and repeating the procedure noted above The design for the later irrigations will be left to the reader to do but as a hint try reducing the number of sets to 9 increasing the cutoff time to 11 hours and reducing the furrow stream to 7 5 gpm 65 Inflow Controls Field Topography Geometry Infiltration Characteristics Hydrograph Inputs Design Panel t T Z kr req reg 9 Initial Later Continuous Continuous Flow Initial Surge Later Surge Flow Flow Conditions Conditions Flow Conditons Conditions Two Point 0534 2 0331 0391 0 405 TL min K ft 3 f mn a 0 03014 003509 0 00476 0 01615 4150 000058 0000958 001897 E C ft 3 ft 0 00000 0 00000 5L ft Qinfilt gpm 31 701 31700 590 6 Tables Tables Tables Simulate E 7 Root Zane Soil Mgisture Depletion zreq inches 3993 2992 3937 Required Intake Opportunity Time min 2 160 559 28 475 English Units V Furrow System Metric Units Border Basin System Figure IV 6 Selecting the later irrigation conditions One of the most difficult aspects of surface irrigation 1s the reconciliation of the water supply characteristics and the on field irrigation requirements It can be observed that in the desi
180. stances 1s less useful Although it should be noted that mini basins formed around each tree and then irrigated pass through or cascade fashion are found many orchard systems Cascading systems are usually less efficient and have low uniformity due to poor water control Basin irrigation 15 also more effective with deep rooted crops like alfalfa than with shallow rooted crops like vegetables Crops which react adversely to crown wetting do not favor basins 1 2 1 7 Cultural Factors Because surface irrigation depends on the movement of water over the field surface whose properties change from year to year and crop to crop as well as from irrigation to irrigation surface irrigation management 15 a difficult task to do well and consistently Basin irrigation reduces this burden by eliminating tailwater from the management process However where basin irrigation has not been practiced previously the added costs and the uncertainty associated with a lack of experience are often substantial barriers to its adoption Basin irrigation 15 less common in the US than either border or furrow systems but has been shown to have significant advantages Nevertheless most irrigators will stay with practices that have been used previously in their area rather than take the risk associated with a new technology Consequently demonstrations are often necessary to introduce basin irrigation One of the criticisms of basin irrigation when used with squar
181. stic shape skewed toward the inlet end of the field Distance From Field Inlel x 0 751 L gt Va Root Zone Siorage V 7 Ta i Under V4 PPE EP EE EEE EL EE EEE PEE PF T gt Deep Percolation Vay Leaching Requirement Vr Figure III 7 Distribution of applied water in surface irrigation The amount of water that can be stored in the root zone is Lxz but as shown some region of the root zone has not received water owing to the spatial distribution of infiltration The depth of water that would refill the root zone 15 beyond which water percolates below the roots and is lost to the drainage or groundwater system Generally these flows return to receiving waters where they can be used elsewhere Thus they are lost in terms of the local condition but perhaps not to the regional or basin locale The negative connotations of loss should be kept even though this water may be recovered and reused The quality of these flows is nearly always degraded and the timing of when they are available elsewhere may not be useful Computing each of these components requires a numerical integration of infiltrated depth over the field length For the purposes of this discussion it 15 convenient to define the components as follows 60 Vin 15 the total depth per unit width or volume per furrow spacing of water applied to the field is the total depth per un
182. t Moisture content on a dry weight basis at which plants can porosity pump back system recession phase recession time t no longer obtain sufficient moisture from the soil to satisfy water requirements and will not fully recover when water is added to the crop root zone Classically this occurs at about 15 atmospheres 15 bars of soil moisture tension The ratio of the volume of pores in a soil volume to the total volume of the sample See tailwater reuse system A term referring to the drainage of water from the field surface following the termination of inflow The interval between the initiation of irrigation and completion of the recession phase Usual units are minutes or hours resistance coefficient n A parameter in the Manning Equation that provides an expression return flow run length runoff run time saturation S siphon tube of hydraulic resistance at the boundary of the flow Deep percolation tailwater conveyance seepage and spills from an irrigation system which flow into local streams rivers lakes or reservoirs Distance water must flow over the surface of a field to complete the advance phase The field length is the longest run length Usual units are feet A general term describing the water from precipitation snow melt or irrigation that flows over and from the soil surface In surface irrigation runoff is used interchangeably with tailwater
183. t of the National Engineering Handbook will not replace these documents but will present a few simple tools and guidelines for the design of head ditches 9 USDA NRCS 1977 Design of Open Channels Technical Release No 25 USDA NRCS 1997 National Engineering Handbook Part 652 Irrigation Guide 98 Head ditches come various configurations lined and unlined and equipped with different ways to divert water onto the field some of which are shown in Fig IV 16 These can be designed so far as capacity is concerned with the Manning Equation Calculator found on the Field Characteristics panel of the input tabbed notebook of the SURFACE software There are three general criteria for effective head ditch design The first is that flatter side slopes are better than steep ones When the head ditch 1s diked up to allow the diversion of water onto the field ditches with flat side slopes have greater storage capacity at the higher ponded depths Most small head ditches have slopes ranging between 1 1 to 1 5 1 The second criterion for head ditch design 1s that the ditch capacity should carry the design flow at two thirds of the ditch s constructed depth when it 15 not diked up for irrigation This will allow offtakes such as spiles and ditch gates to be located above the water level in the areas of the field not being currently irrigated The third criterion is that the maximum depth the ditch should not exceed 90 of the constr
184. ter is known It is no longer necessary to approximate neither Manning nor the furrow shape Consequently the reference state for any furrow intake measurement 15 the flow and wetted perimeter in the furrow at the time of the measurement Any adjustment for different flows or different shapes and wetted perimeters on the same soil should be made on the basis of an adjusted wetted perimeter and not the furrow spacing The revised intake families of Section III are based on this modification A 4 3 Converting Between Border Basin Infiltration and Furrow Intake At the time of this manual preparation the number of furrow intake measurements available for evaluation in the general sense is substantially greater measurements 114 corresponding to border basin irrigation Consequently it 15 suggested that the historical practice found in earlier NRCS documents in which the furrow intake is derived from border basin infiltration should be reversed Furthermore it is no longer realistic to ignore the intake characteristics of the initial irrigations In this manual the reference intake family has been based on the estimated 6 hour intake rates of freshly formed furrows with a corresponding reference flow and wetted perimeter Estimates of border basin infiltration curves are then derived by multiplying the furrow and F and parameters by the ratio of furrow wetted perimeter to the unit width to determine their border basic counterparts an
185. tes for later irrigations However from the earlier simulation in which more than 26 of the inflow as deep percolation the 3 inch application 1s probably too small A more realistic value 15 4 inches As a starting point assume the values of x and w Eqs IV 3 and IV 4 0 70 and 1 15 respectively Accordingly the times of cutoff can be estimated to the nearest on half hour as 330 minutes and 420 minutes respectively after rounding to the half hour From Eq IV 4 the volume needed to replace the soil moisture depletion is 460 ft ft so that from Eq IV 5 the unit inflow should be 0 023 cfs ft 1nitially 460 7 330 min 60 sec min and then 0 018 cfs ft later If these values are simulated the SURFACE software the results shown in Figure IV 11 indicate an irrigation efficiency of more than 80 in both cases but the uniformity 1s poor near the end of the field Succeeding iterations can be simulated by making small adjustments to the cutoff time and the inflow but these will produce only small improvements Further improvements will require either shortening the run length or flattening the lower 25 of the 90 field to improve uniformity at the end of the field Flow Depth Surface amp Subsurface Flow Profiles Initial Irrigations Flow Depth Surface amp Subsurface Flow Profiles Later Irrigations Figure IV 11 Simulation of the BlockedEndBorder data IV 3 3 Design Procedure for Cutback Systems The
186. th 1181 Design Flow gprm mt Width Results No of Sets 32 000 Application Efficiency 47 55 1 Efficiency 52 b EUM Hequirement Efficiency 4 99 36 Distribution Uniformity 2 93 56 Tailwater Fracton 1 02 ES VEHIT Deep Percolation Fracton 51 44 2362 Design Data anm Desa Fares Figure 4 SURFACE Design Panel for initial FreeDrainingFurrow 1 condition 84 The first observation that can be made is the total flow required to irrigate the entire field simultaneously shown in red is more than 30 000 gpm which is more than 12 times the flow available 2400 gpm Click on the right field layout up down button l until the conflict between available flow and required flow 15 resolved by irrigating in sets Thirteen sets are required to satisfy the flow constraint but in doing so total time the supply needs to be available has increased to 104 hours whereas only 96 hours are allowed Consequently there does not appear to be a feasible design option irrigating the full length of these furrows In cases where both time and flow constraints be managed the next step would be to determine if different flows and cutoff times would improve the irrigation Thus the next redesign option 15 to change run length This can be accomplished clicking on the left up down button l to cut the run length in half Then the furrow stream size can be reduced
187. the initial irrigations Changes due to previous irrigations have been estimated from field experience and expressed as a modification of the reference family 3 The intake families are denoted with numbers varying from 0 02 to 4 00 These family categories are the average infiltration rate over the first six hours of irrigation For initial continuous flow irrigations the average 6 hour intake rate 1s essentially the same as the family designation but 6 hour intake rates for subsequent irrigations are less The Table III 2 below shows the average 6 hour intake rates for each soil and irrigation regime 4 effect of surge flow for initial irrigations 1s approximately the same as the effect of previous irrigations under continuous flow Intake under surge flow systems during subsequent irrigations 1s based on adjustment of the initial irrigation surge flow intake 5 t has been assumed that the exponent a Eqs 14 and 15 are the same value 1 the a exponent 15 the same for furrow and border basins for each soil A comparison of the total 6 hour cumulative intake for the reference family and the three other furrow irrigated conditions 1s shown Fig III 4 The intake parameters for furrows are shown in Tables III 3 III 6 A review of how the original SCS intake families were developed 15 included in Appendix 53 TABLE 2 AVERAGE 6 HOUR INTAKE RATES FOR THE FURROW BASED REFERENCE INTAKE FAMILIES NRCS
188. tion Downstream Boundary Free Draining Flow Cross Section Top Width 0 360 Middle Width m 0 280 Bottom Width 0 100 Maximum Depth 0 120 Furrows Manning n First Irrigations 0 040 Later Irrigations 0 030 Base Compound Slopes First Slope 0 00800 Manning Equation Calculator Rhol Second Slope 0 00800 Slope 0 00000 Rho2 Third 5lope 0 00800 Manning n 0 0000 Sigmal First Distance m 360 0 Bhp He 0 0000 Sigma2 Second Distance m 360 0 Depth m 0 0000 Gammal The First Distance is the distance Area m 0 0000 2 from field inlet to the break in slope Cmh between First Slope and Second Top Width m 0 0000 ud on on C d orhe Ee Wetted Perimeter m 0 0000 Figure II 3 The SURFACE input tabbed notebook 3 3 Output The SURFACE software includes tabular as well as graphical presentation of simulation results These options can be accessed from the main menu by clicking on Output and then choosing displayed numerical or plotted results File Input Units Simulate Design ES Display Output Results m al Lar Two speed buttons are also available for displayed and plotted E results Figure II 4 illustrates the displayed data window Both will be discussed more in sections below II 3 4 Units The input data and results of simulation design and evaluation can be displayed in metric or English units This 1s a user
189. tion Since its introduction in 1979 surge flow has been tested on nearly every type of surface irrigation system and over the full range of soil types Results vary depending on the selection of cycle time cycle ratio and discharge Generally the intermittent application significantly reduces infiltration rates and thus the time necessary for the infiltration rates to approach the final or basic rate To achieve this effect on infiltration rates the flow must completely drain from the field between surges If the period between surges 15 too short the individual surges overlap or coalesce and the infiltration effects are generally not created The effect of having reduced the infiltration rates over at least a portion of the field 15 that advance rates are increased Generally less water 1s required to complete the advance phase by surge flow than with continuous flow Surging 15 often the only way to complete the advance phase in high intake conditions like those following planting or cultivation a result intake opportunity times over the field are more uniform However since results will vary among soils types of surface irrigation and the surge flow configurations tests should be conducted in areas where experience 15 lacking in order to establish the feasibility and format for using surge flow 1 3 7 2 Surge Flow Systems The original surge flow system involved automating individual valves for each furrow using pneumatic controls
190. tion of applied water percolating below the root zone 7 5 Printed Output A printout of the principle input data and a graphical print of the design panel can be i rry obtained by clicking the tint Data This Desi Fore faint input Date and this Design Panel button The graphical printout of the design panel will be the same as illustrated in Fig 16 and will require a graphics capable printer IL8 SAMPLE DATA SETS 8 1 FreeDrainingFurrow_1 cfg FreeDrainingFurrow 1 data set describes a 64 acre furrow irrigated field supplied by a well with a capacity of 2400 gpm The furrows are irrigated on 30 inch spacings The soil is a silt loam with an average 6 hr intake rate of 0 2585 ft f hr which within the 2 5 foot furrow spacing 15 1 24 in hr Curve No 1 00 1 50 The target depth of application is 4 inches The furrow stream is 32 gpm with a 8 hour cutoff time The maximum non erosive velocity of 39 feet min was taken from the table shown earlier A simulation of these data reveals that substantial over irrigation occurs at the upper end of the field and substantial under irrigation occurs at the downstream end The application efficiency is about 48 primarily because more than 51 of the inflow was lost in deep percolation For a 4 inch irrigation it would require only 160 minutes to infiltrate the desired depth The 8 hour cutoff time 15 necessary to allow completion of the advance time 8 2 Fre
191. to be increased If F is initially set to zero and the resulting volume of infiltration from Steps 1 3 above 15 too low the values of a and as good as the volume balance can provide A revised value of should be made based the error in the infiltrated volume and steps one two and three repeated using revised values of the Kostiakov Lewis parameters When the least error is produced the best estimate of the average field intake has been made with the volume balance methodology III 3 2 5 Example To demonstrate this procedure open an application of SURFACE and load the data file designated as FreeDraining Furrow 2 cfg and then open the input notebook by clicking on the input button 5 Select the Input Control panel and click the Continuous Inflow Hydrograph radio button Then simulate the system by clicking on the run button The resulting in the advance recession plot 1s shown in Figure III 11 and the tailwater hydrograph 1s shown in Figure III 12 Except for the recession curve the hydrograph data in the FreeDrainingFurrow 2 cfg data set are not simulated too well and the intake parameters need to be adjusted Actually the hydrograph data were derived from different from a furrow of similar characteristics but different intake parameters Note that the inflow for the hydrograph data 1s 0 033 cfs whereas the intake parameters in the data set were derived from an inflow of 0 022 cfs In order to calibrate the i
192. traints on the design procedures Many fields will require a subdivision to utilize the total flow available within a period of availability This 1s a judgment that the designer must make after weighing all other factors that are relevant to the successful operation of the system Maximum efficiencies the implicit goal of design will occur when the least watered areas of the field receive a depth equivalent to Minimizing differences in intake opportunity time will minimize deep percolation and maximize uniformity Surface runoff should be controlled or reused The design intake opportunity time 1s defined in the following way from Eqs III 17 and III 18 Z C for furrows req IV 1 ftu for borders and basins lt req o req where 4 4 is the required infiltrated volume per unit length and per unit width or per furrow spacing and is the design intake opportunity time In the cases of border and basin irrigation Zreq 15 numerically equal to However for furrow irrigation the furrow spacing must be introduced to reconcile and Zreg as follows 78 2 where w 1s the furrow to furrow spacing Whether the irrigation specialist 15 designing a new surface irrigation system or seeking to improve the performance of an existing system the design should be based on careful evaluation of local soil topography cultural and climatic conditions The selection of system conf
193. ucted depth This criterion will come into focus as the ditch 1s diked to divert water onto the fields and therefore the design of offtakes should be such that the total flow can be diverted without exceeding the 90 limit The remaining 10 of the ditch depth is freeboard and 15 necessary as a safety measure For example in Section 3 2 1 Blocked End Border Example the flow required from the main supply was 10 0 Width 114 000 If it 1s assumed that the head ditch is to be a trapezoidal concrete ditch running on the 0 0001 cross slope then the question 1s what the ditch dimensions should be It should be kept mind that only certain sizes of these ditches may be Maximum Depth 36 000 available from local contractors due to equipment limitations For the purposes of this example a ditch with a 3 foot depth a 2 foot bottom width a slope of 1 25 1 and a Manning n of Manning Equation Calculator 0 018 a typical value concrete ditches can be ins 0 00010 selected Then using the Manning Equation Calculator in a 0 0180 trial and error manner a channel can be designed Flow cis 10 0001 Middle Width in 69 000 Bottom Width in 24 000 As be seen at the right this ditch would carry 10 cfs flow at a depth of 2 236 feet which is slightly more than 2 2382 the 2 0 feet specified under the two thirds rule noted above Area ft 2 10 8773 I
194. uring the wetting or ponding phase to control runoff Cumulative time since the initiation of irrigation until the inflow is terminated Also referred to as set time Usual units are minutes or hours Length of water application periods typically used with surge irrigation Usual units are minutes The depth or volume of water percolating below the root zone The depth or volume of deep percolation divided by the average depth or volume of water applied to a field 1s the deep percolation ratio DPR The practice of deliberately under irrigating a field in order to conserve water or provide a capacity to store expected precipitation The elapsed time between the initiation of irrigation and the recession of water following cutoff at the field inlet Usual units are minutes The network of ditches or pipes and their appurtenances which convey and distribute water to the fields Constructed open channel for conducting water to fields Small controlled opening or portal in a ditch used to divert water directly to furrows borders or basins distribution uniformity DU See uniformity effective precipitation Portion of total precipitation which becomes available for plant growth evapotranspiration see consumptive use fertigation field bay field capacity Wf field length flow rate q Q flood irrigation furrow irrigation gated pipe head ditch infiltration infiltration rate 1 infi
195. urn the inflow off what the field slope should be as well as its length what structures and facilities are needed and what should be done about tailwater if the field is to allow it At the operational stage the questions are what the unit flow should be and when it should be shut off In other words water management in surface irrigation systems involves both design and operational questions that involve the same set of parameters The following are some general guidelines More specific tools will be presented subsequent sections 1 3 1 Choosing a Surface Irrigation System The eight factors discussed under basin furrow and border irrigation above will generally dictate the type of surface system that should be employed in a particular situation but the irrigation specialist advisor or extension agent should not be surprised if it is not the last factor a cultural factor that 15 the deciding factor The crops to be irrigated may determine the system immediately For instance 1f paddy rice 1s the major crop basins will nearly always be the logical choice Not always however Some rice areas in the southern US prefer low gradient blocked end borders to facilitate drainage and to better accommodate second crops like corn Future water quality goals for watersheds may be such that the surface irrigation systems must have a higher efficiency than can be achieved with furrows and therefore dictate basins blocked end borders or furrow s
196. vailable flow as follows LW L R where is the number of sets required to irrigate the field 1 the width of the field w is the unit width in the same units as is the total available flow is the design flow in same units as L is the length of the field and Rz is the run length in the same units as L As an example suppose the field is 2361 feet in width and should be irrigated by furrows spaced at 3 foot intervals and with a unit flow of 24 gpm The field is 1180 feet long but will be subdivided into 590 foot long furrows If the available flow to the field is 2376 gpm the number of sets will be 8 _ 24 2361 feet 1180 feet 2376 3 feet 590 feet 7 1 2 Total Time Flow is Available Depending upon the policies of the delivery system there may be a limit on the time the flow will be made available to the field For instance many systems operate on a rotational delivery scheme where the field can receive water every 7 21 days for a fixed number of hours Suppose the set time or the time required by each set to completely irrigate it is 4 hours or 240 minutes The time needed to irrigate the entire field 15 T N t l6sets 4 hrs set 64 hours in which 77 is the total required time and tco is the cutoff time for each set 40 The required total time to irrigate the field has to be less than the actual total time the flow 1s available or else the
197. w long it takes the water to reach the end of the furrow In addition some furrows are compacted by the wheel traffic of planting and cultivation equipment and have substantially different characteristics non traffic furrows Irrigators compensate by adjusting the furrow flows and thereby need to be at the field longer Further they also have to assess how long to allow the water to run off the field before shutting it off as opposed to shutting the flow off in a basin when the correct total volume has been added to the field Because most furrow systems allow field tailwater they are seldom as efficient as basin systems and thereby require more water per unit area Measures such as the capture and reuse of tailwater can be employed to increase efficiency Another alternative is a concept called cutback that involves reducing the furrow inflow after the flow has reached the end of the furrow Surge flow and cablegation systems are examples of automated cutback systems 1 2 2 2 Field Geometry Furrow irrigated fields generally have slopes in both the direction of the flow and the lateral direction These slopes can vary within a field although the slope in the direction of flow should not vary significantly unless it 1s flattened at the end of the field to improve uniformity Figure I 5 illustrates the use of contour furrows to irrigate irregularly sloped fields One of the major advantages of furrow irrigation 15 that undulations in topography
198. y being irrigated the tailwater reuse design is somewhat more complex than the procedure for traditional free draining systems because of the need to utilize two sources of water The major complexity of reuse systems 15 the strategy for re circulating the tailwater One alternative 15 to pump the tailwater back to the head of the field it originated from to irrigate some part of the field Or water captured from one field can be reused on another field In any case the tailwater reservoir and pumping system need to be carefully controlled and coordinated with the primary water supply Experience suggests that the costs of water from tailwater recycling can be as much as ten times the cost of water from an irrigation company or irrigation district Further the recycling system can be so difficult to manage and maintain that irrigators abandon them resolve these and related problems it 15 suggested that recycling be very simple irrigate the field it originates from primarily and not be mixed with the primary supply but rather irrigate a portion of the field independently To illustrate the design strategy for reuse systems a manual design procedure for this simple configuration 15 first presented and following an example using the SURFACE software A typical reuse system shown 15 schematically in Fig IV 13 and 15 intended to capture tailwater from one part of the field and irrigate one of the sets 93 Main Water Head Ditch _ Supply
199. ystems with tailwater reuse In many cases there may not be a definite advantage associated with any form of surface irrigation The system selected must be based on farmer preference cropping pattern or environmental constraints Land leveling is nearly always the most expensive operation on the field itself and choosing a border or basin system over a furrow system must consider these capital costs in lieu of the savings in operational costs like water labor and maintenance that emerge over a period of years Consequently leveling costs are probably the first indicator Consider for example a field that would require 300 per acre to level it for basins If the water cost is 15 per acre foot a not unusual figure 1 would require many years to recapture the investment costs of the leveling with water savings alone On the other hand 17 labor 15 critically expensive and short perhaps the basins would be a more feasible choice In short if a change in surface irrigation system 1s contemplated examining the leveling costs after considering cultural factors will prove useful 13 2 Inlet Discharge Control Practices There is an interesting trade off between the inflow rate and the time of cutoff which influence uniformity and efficiency differently If the discharge per unit width 15 too small the water will advance very slowly over the field resulting in poor uniformity and low efficiency The problems with uniformity will be due to the large differ

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