7 FURDEV user manual
Contents
1. Determining a kind of average furrow infiltration parameter from Field data on advance times For more background information on this subject see Chapter 3 Section 1 1 The default infiltration input mode is Intake family Geometry All surface flow calculations in the program are based on the furrow geome try expressed in terms of the furrow geometry parameters 01 02 T1 and T2 For more information on these parameters see Section 7 2 1 and Appendix B In the sub sub menu Geometry these parameters can be specified under the Sigma amp tau option Because of the complexity of these parameters how ever FURDEV also offers you the option Cross section type where you can simply indicate one of three cross sectional shapes that is the closest match to the real cross section of the furrow Here you can choose between Triangular Parabolic or Trapezoidal Figure 7 1 Later on in the input windows you will be required to specify the characteristic data for the selected cross section Fl Help Select triangular cross_section Figure 7 1 Selecting a furrow cross section in Furdev 87 eg flow depth side slope top width etc Using these data the program will calculate the corresponding furrow geometry parameters o1 02 T1 and 79 The default geometry input mode is Cross section type and the default furrow cross section shape is Triangular 7 1 5 Sub menu calculation The sub menu Calculation is the o2. Finally there are two groups of secondary output variables in all the calcu lation modes These concern times and depths and are advance time deple tion time recession time and intake opportunity time corresponding to the downstream point Note all the time values are counted from zero ie from the start of the irrigation The duration of a phase is the difference between two times for instance the duration of the depletion period equals the deple tion time minus cutoff time In all calculation modes FURDEYV provides information on the maximum minimum and average infiltrated amounts together with the surface runoff In addition Mode 4 also presents the amount of over and under irrigation as the average amount over that part of the furrow where this has occurred and includes the length of the furrow segment on which it occurs The output results shown are dependent on the combination of Operation and Calculation modes Table 7 4 shows the output results for the operation mode Fixed flow The program also presents the same output results for the Table 7 4 Output results for the Furdev calculation modes Fixed flow system Output parameters Mode 1 Mode 2 Mode 3 Mode 4 Design variables Furrow length o Flow rate o Cutoff time o o 0 Minimum infiltrated depth O Primary performance indicators Application efficiency o o o Oo Surface runoff ratio o o o o Deep percolation ratio O o o o Storage efficiency o Distribution
3. and the minimum flow rate is deter mined by advance considerations Hart et al 1980 Apart from these more theoretical assumptions related to the algorithm and its solutions ie accepting the model as it is the following practical con ditions are assumed for the use of FURDEV The inflow rate is constant during the entire application time apart of course from a possible reduction in case of a cutback operation The soil is homogeneous throughout the length of the furrow The roughness coefficient is constant in space and time The cross section is constant over the furrow length The cutoff time is always greater than advance time The furrow slope is uniform along the length The simulation results obtained with FURDEV will be much in line with field observations provided that the field conditions match the assumptions made in the program and that the consequent limitations are respected As stated in the other programs FURDEV only deals with the technical and hydraulic aspects of furrow irrigation The program should therefore be regarded as an aid in the design operation and evaluation In addition to the findings of the program final decisions in the field will be affected by agricultural economic and social considerations 100 7 6 Program usage The following 10 steps are important in the usage of the FURDEV program 1 2 10 Start the SURDEV package Select FURDEV from the main menu of
4. for the remainder Table 7 1 Furdev menu structure Files Operation Units Parameters Calculation Quit Load Fixed flow Flow rate Infiltration 1 Flow rate View Print Cutback flow Length Geometry 2 Length Tailwater reuse Amount depth 3 Cutoff time Time 4 Min Amount 85 of the application time Tailwater reuse represents a furrow irrigation system with a runoff reuse arrangement Because FURDEV only simulates the flow in one furrow the reuse component is not integrated in the required flow rate of another furrow The default operation mode is Fixed flow 7 1 33 Sub menu units In the sub menu Units you can choose pre determined units for flow rate length amount and time The following units are available Flow rate litres per second US gallons per minute cubic metres per minute or cubic feet per minute Length metres or feet used for furrow length Amount depth millimetres inches cubic metres per metre length of fur row or cubic feet per foot length of furrow These are used for the various supplied and infiltrated amounts or depths Time minutes or hours used not only for advance cutoff deple tion and recession times but also in the infiltration parameters Because FURDEYV simulates the flow in one furrow the spacing of the furrows is a parameter for the actual amount of infiltrated irrigation water When you select millimetres or inches the quantity of infiltrated irrigation water is expr
5. furrow length that is needed to achieve a reasonable performance The program will also give you the required cutoff time and the primary performance indicators as well as vari ous depth and time parameters Here too it is necessary to continue in Modes 3 and or 4 to get the final result Calculation Mode 3 Cutoff Time Here both the flow rate and furrow length are input The required cutoff time is the resulting design variable while also the application efficiency and sec ondary output parameters are given Note in this mode the advance ratio is an output This is because it is impossible to fix advance ratio length and flow rate and at the same time satisfy the requirement that the minimum infiltrated depth equals the required depth 88 Calculation Mode 4 Minimum Depth Here the cutoff time is also specified as input in addition to the furrow length and the flow rate Thus all design variables are now input which means that the required depth at the end of the field will usually not be achieved ie that under and or over irrigation can occur The minimum infiltrated depth that occurs at the far end of the field is the determining factor of whether there is under or over irrigation It is therefore given as first output followed by the primary performance indicators application efficiency storage efficiency and distribution uniformity This mode is most suitable for a performance evalua tion of an existing furrow irrigat
6. in order to get a result For output results the above ranges are ignored So if such an out of range value is subsequently used as input in another mode no warning will be given 7 3 Output windows After all the input has been entered press F2 for the calculations and the output The screen again shows the three input windows but a fourth window has now been added showing the results Figure 7 3 These results are pre sented in various groups separated by a blank line The first group contains the desired decision variable or variables according to the calculation mode you have selected in Mode 1 they are the flow rate and the cutoff time in Mode 2 the furrow length and cutoff time in Mode 3 the cutoff time and i in Mode 4 the minimum infiltrated depth The second group contains the primary performance indicators as discussed in Chapter 3 Section 3 All the calculation modes allow the performance of an irrigation scenario to be evaluated with the application efficiency the surface runoff ratio the deep percolation ratio the distribution uniformity and the uniformity coefficient Mode 4 adds the storage efficiency Note the first three indicators also represent the overall water balance of the furrow FUD PARARISUIaR Di Cut off time Applic efficiency Wsurf run off ratio Deep perc ratio Distr uniformity Unif coefficient F3 Graph F4 Save PgDn Next window Figure 7 3 Results screen in Furdev 95
7. option of just specifying the furrow shape by selecting Cross sectional type If you select Triangular as the cross sectional shape the input window will ask you to specify only the side slope of the furrow cross section If you select Parabolic you need to specify the maximum depth and the corresponding water top width either estimated or obtained from field measurements If you select Trapezoidal you need to enter the side slope and the bed width For all three cross sectional shapes the program will transform the given input values into the corresponding geometry parameters 61 o2 T1 and t2 You can check this by selecting a particular cross sectional shape entering the required input data making a run going back to the sub menu Parameters selecting Geometry and Sigma amp tau mode and returning to the input win dow again When selecting the geometry shape and geometry parameters care should be taken that the geometry and spacing are not conflicting For instance the combination of small spacing with a wide and deep trapezoidal section may be geometrically impossible In such cases if impossible combinations are 91 entered as input FURDEV will flash you a message to that effect on your screen see Section 7 4 Infiltration When the Intake family type of infiltration data is selected FURDEV uses the modified SCS families for furrows as was discussed in Chapter 3 Section 1 1 Seventeen families can be chosen If a
8. run output and input in one file in a separate file or append them to earlier runs in an existing file by pressing F4 Select Files and View Print from the main menu to see what has been done and or to print a file directly or convert it to a print file for a word processor program or convert it to a file to be imported into a spread sheet program where you can make your own graphs 7 7 Sample problems In most cases users will not be satisfied with a solution obtained after one run and will usually do a number of runs to get an acceptable solution Two simple examples are given to illustrate this procedure More elaborate prob lems can be found in Chapter 8 Section 3 101 7 7 1 Determine furrow length A design combination is to be developed for a fixed flow furrow irrigation sys tem in which the available inflow rate into the furrow is fixed at 1 V s The soil is silty loam and can be classified by the Intake Family 0 6 The value of the flow resistance is fixed at 0 04 The net irrigation requirement is 100 mm The furrows have a triangular cross section with a side slope of 1 1 a slope of 0 008 and a spacing of 75 cm Determine the furrow length in such a way that the application efficiency is at least 70 per cent and the cutoff time has a prac tical value The maximum feasible furrow length is 600 m in the direction of the main field slope 1 We want to make a new file and therefore do not need to use the Fil
9. therefore include the two dimensional infiltration process In other words these parameter here should have been obtained from furrow infiltration trials and do not represent the infiltration characteristics of the soil for a flat surface Converting the intake parameters to values other than default units can be done as follows Go back to the Units menu change time and amount depth units and return to the Field Parameters input window where the new val ues and their units will appear When the Field data option is selected enter the data obtained from field infiltration tests as input based on which FURDEV will calculate the corre sponding infiltration parameters Logically these are the furrow infiltration parameters already including the two dimensional aspect To estimate the infiltration parameters of the modified Kostiakov equation the two point method Elliott and Walker 1982 is applied in the program The data you now need to prescribe are flow rate stable tailwater runoff the runoff rate after the runoff hydrograph levels off advance time to downstream end of furrow advance time to halfway down the furrow furrow length and furrow bed slope Note only the spacing belonging to the field measurements must be 92 entered under parameters Field For more information on this option see Appendix B The above difference between soil parameters and furrow parameters implies that one has to be carefu
10. wrong number is typed you will get an error message on your screen with a list of acceptable numbers To select a particular family you can get Help by pressing F1 while the cursor is on the family number A help screen will pop up from which you can make your selec tion using the upward and downward arrow keys Upon selection of a family number the corresponding values A k and fy of the Kostiakov Lewis equation as shown in Table 3 3 will give you the soil infiltration parameters as determined from infiltrometer measurements for instance To simulate the furrow infiltration these are converted to furrow infiltration parameters In furrows infiltration takes place along the wetted perimeter of the furrow and is assumed to spread in the soil over the width of the furrow spacing see Jensen 1980 and Walker 1989 The values of Table 3 3 are therefore adjusted by using the ratio of wetted perimeter to furrow spacing Once you make a run with FURDEYV this is automatically done with in the program You can check this by selecting a family number making a run going back to the sub module Infiltration selecting the Kostiakov Lewis equation mode and returning to the input window again where you then see the adjusted furrow infiltration parameters When you select the Kostiakov Lewis equation you can specify the values of the intake parameters A k and f directly Note these values represent the furrow values and
11. 7 FURDEV user manual FURDEV is a modular menu driven computer program developed to solve problems in the design operation and evaluation of furrow irrigation systems FURDEV deals with the flow in one furrow and does not provide suggestions for field layout design You start the program by selecting it in the SURDEV package The installation procedure of this package was discussed in Chapter 4 Section 1 7 1 Menu structure There are six main menu items five of which have sub menus that you can select by moving the highlight with the arrow keys and pressing ENTER or by typing the red bold character Table 7 1 shows the structure of the main menu and its first layer of sub menus 7 1 1 Sub menu files The sub menu Files has two options Load and View Print With Load you can select an existing file and continue with the calculations With View Print you can select an existing file the contents of which will subse quently be displayed on the screen Pressing F5 gives you the option to print this file or to save it as a text file or a spreadsheet file For more information on these topics see Chapter 4 Section 4 3 7 1 2 Sub menu operation You can select the appropriate system operation mode from the sub menu Operation Selecting Fixed flow means that a constant inlet flow rate is used to irrigate the furrows during the entire application time Cutback flow means that at the end of advance the initial inflow is reduced once
12. DEV but also provide you with a deeper insight into the complex nature of the furrow irrigation process 104 Table 7 6 Furdev program for furrow irrigation File name EXAMPLE2 Run no Type of system Calculation mode Input data Flow rate Length Cutoff time Required depth Flow resistance Furrow slope Furrow spacing Maximum velocity Side slope Intake family Output data Flow rate Cutoff time Application eff Storage eff Uniform Coeff Distrib Unif Deep perc ratio Runoff ratio Advance time Depletion time Recession time Opportunity time Avg inf Depth Max inf Depth Min inf Depth Surface runoff Over irr Under irr Over irr Length Under irr Length min 400 100 0 04 0 008 0 75 13 8 0 6 2 1 4 1 21 400 480 100 0 04 0 008 0 75 13 8 0 6 84 97 91 75 243 486 534 291 106 116 80 10 12 283 117 n 1 5 400 480 100 0 04 0 008 0 75 13 8 0 6 69 100 95 88 11 20 157 486 538 381 115 121 101 29 15 400 _ 1 5 400 420 100 0 04 0 008 0 75 13 8 0 6 105
13. SURDEV If you want to use an existing file retrieve it with the Load command under the Files menu If you want to make a new file go straight to the Calculation menu bypassing the Files menu and you will get a set of default data If you want to simulate Cutback flow or Reuse go to the Operation menu and select the operation mode to work with The program default opera tion mode is Fixed inflow Select the Units menu only when you want to work with units other than the default units The default infiltration mode is the Modified SCS families If you want to work with another infiltration mode go to the Parameters menu and select the Infiltration menu The program default geometry is the triangular cross section under the heading cross sectional shapes Changes can be made under Parameters and Geometry Select a mode to work in from the Calculation menu Most work will be done in Modes 3 and or 4 Less experienced users can start in Mode 1 or 2 to get a first estimate of the flow rate or field dimensions respectively and then continue in Mode 3 and or 4 Mode 4 can be used to evaluate an existing situation or to do sensitivity analyses You can specify field parameters and decision variables in the input win dow after which the program can be run by pressing the key F2 You can view the results of each run in tabular form in the output win dow or in graphical form by pressing F3 You can save the results of one simulation
14. advance time requirement by selecting the appropriate value of flow rate in Mode 1 or furrow length in Mode 2 In Calculation Mode 1 the advance time associated with the maximum non erosive flow rate can be longer than that of the required advance time In such a situation the required advance time cannot be achieved without using a flow rate that is greater than the maximum non erosive one This is clearly unacceptable The only way out of this problem is to reduce the furrow length and or increase the advance ratio In addition there are cases in which the flow rate corresponding to the required advance time is less than the mini mum flow rate required to advance to the downstream end of the furrow When this happens FURDEV will advise you to increase the furrow length and or the advance ratio In Calculation Mode 2 with some parameter and variable combinations it is possible that the required advance time is greater than the advance time that corresponds to the maximum length to which the user specified flow rate can advance To overcome this difficulty FURDEV will recommend that you increase the flow rate and or decreasing the advance ratio Cutoff time problem In Calculation Modes 1 2 and 3 the cutoff time is RE so that the min imum infiltrated amount is equal to the required amount In Mode 4 the cut off time is an input If the user specified cutoff time is too short it is possible that the calculated advance time will exce
15. cent and the distri bution uniformity is 86 per cent Over the lower 75 m of the furrow the average depth infiltrated would be 4 mm less than that required The upper 225 m of the furrow would receive an average over irrigation depth of 8 mm These results are acceptable Table 7 5 can be made with FURDEV The procedure is as follows Save Run 1 with F4 and prescribe a particular file name EXAMPLE1 FURDEV auto matically adds the extension FDR to this file name Save Runs 2 and 3 with F4 under the same file name using the Append option Go back to the main 102 Table 7 5 Furdev program for furrow irrigation Filename EXAMPLE1 Run no Type of system Calculation mode Input data Flow rate Length Cutoff time Required depth Flow resistance Furrow slope Furrow spacing Maximum velocity Side slope Intake family Output data Flow rate Length Cutoff time Application eff Storage eff Uniform coeff Distrib unif Deep perc ratio Runoff ratio Advance time Depletion time Recession time Opportunity time Avg inf depth Max inf depth Min inf depth Surface runoff Over irr Under irr Over irr Length Under irr Length min e 338 596 71 100 93 16 14 226 602 647 421 122 131 100 19 22 338 _ 300 100 0 04 0 008 0 75 13 8 0 6 536 70 100 95 87 10 20 163 541 584 421 115 121 100 28 15 300 _ 300 480 100 0 04 0 008 0 75 13 8 0 6 T
16. e sum of deep percolation losses and surface runoff losses is at its minimum Cutoff time For all three irrigation methods cutoff is usually done some time after the end of advance to achieve infiltration of the required depth at the downstream end If the cutoff time is much later than the advance time it will have a clear effect on the deep percolation and surface runoff losses If cutoff is too early this will often result in not achieving the required depth at the end of the field Cutback ratio The cutback ratio defined as the ratio of reduced flow rate to the initial flow rate must be such that the reduced flow is sufficient to keep the entire field 93 length wetted for as long as is necessary while at the same time reducing the surface runoff In the simulation process cutback is assumed to be done when the water has reached the end of the field Advance ratio n The advance ratio defined as the ratio of advance time to cutoff time is of spe cial interest with cutback systems where it can be simulation input or output depending on the purpose of the simulation Too low a ratio means too short a cutoff time and a high ratio a long cutoff time both with the consequences mentioned under Cutoff Time A small advance ratio means a fast advance and hence a higher flow rate which is generally recommendable Tailwater reuse ratio The tailwater reuse ratio giving that part of the surface runoff that is reused allows u
17. ed it This is a situation that cannot be handled by FURDEV When such a problem is encountered the screen message will recommend decreasing the furrow length and or increasing the flow rate and or increasing the cutoff time Check furrow cross section The message is generated based on an assumed furrow depth of 20 cm and a ridge width of 20 cm For the given side slope of a triangular furrow of 1 5 1 the furrow spacing should then be 2x1 5x20 20 80 cm If your spacing input 98 value is less than this 80 cm this message appears on the monitor together with the results of the simulation Spacing and section are incompatible This message deals with the same geometrical check as explained above but instead of the assumed furrow depth the actual flow depth calculated in the simulations is used considering no freeboard The width of the ridge is still assumed to be 20 cm If the input furrow spacing is less than the calculated required minimum one the message that will appear on the monitor is spac ing and section are incompatible meaning physically impossible Therefore you will get no results and will have to change one of the input values Calculated flow velocity is more than maximum permissible The meaning of this message is obvious The flow velocity calculated by the program is more than the permissible value of the input field parameters Nevertheless the calculation results will show up on the screen The idea is that you
18. es sub menu Note the default operation units and parameter modes must be used in this problem so you can go directly to the Calculation menu and select Mode 2 Furrow length Enter the above values in the two input win dows and make a run F2 2 The results of this run Table 7 5 Run 1 show that with an available flow rate of 1 Vs a furrow 338 m long can be irrigated with an application effi ciency of 71 per cent This requires a cutoff time of 596 minutes The cor responding uniformity coefficient is 93 per cent and the distribution uni formity is 82 per cent From these values it will be clear that a furrow length of 600 m is too long for an application efficiency of 70 per cent Suppose the field can be divided into two parts each 300 m long Run FURDEV in Mode 3 to see the effect when the furrow length is reduced to 300 m 7 3 The results of this run Table 7 5 Run 2 show that a slightly shorter fur row reduces the application efficiency from 71 to 70 per cent which is acceptable The cutoff time however has an impractical value 536 min Run FURDEV in Mode 4 to see the effect when the cutoff time is reduced from 536 to 480 minutes 4 The results of this run Table 7 5 Run 3 show that this reduction in cut off time results in a slight under irrigation the minimum infiltrated depth is now 90 mm instead of 100 mm while the uniformity coefficient is 95 per cent The application efficiency has increased to 77 per
19. essed as the depth of water and the program transforms this value inter nally to a volume per metre length of furrow by taking into account the select ed furrow spacing When you select cubic metres or feet per metre or foot length of furrow then the actual depth of infiltrated irrigation water will depend on the chosen spacing of the furrows The selected units are maintained throughout the program and are also saved with the file When the program is started default units are litres per second for flow rate metres for furrow length millimetres for infiltrated depths and minutes for time 7 1 4 Sub menu parameters The sub menu Parameters allows you to select the mode in which you want to characterise the infiltration characteristics of the soil Unfiltration as well as the geometry of the furrow cross section Geometry Infiltration Within the program all infiltration calculations are based on the infiltration characteristics of a soil as described by the Kostiakov Lewis equation Equation 3 4 86 D kT foT where Dj is the cumulative infiltration depth after an infiltration opportunity time T k is the infiltration constant A is the infiltration exponent and fo is the basic infiltration rate The menu offers three options for entering the soil infiltration characteristics These are Indirectly by using Intake family Directly by specifying values for A k and f in the Kostiakov Lewis equa tion
20. i 99 95 86 18 163 485 528 365 105 111 23 225 75 menu then to the Files menu and select View See the results and select F5 Print Save and then use the option Text file FURDEV now automatically adds the extension TXT to the file name EXAMPLE1 If you now go out of FURDEYV you can load the results in a word processing program by retriev ing the file EXAMPLE1 TXT The above problem uses the Fixed flow operation mode Nevertheless a similar line of reasoning can be employed in the use of the other two opera tion modes 103 7 7 2 Determine flow rate A design is to be made for an existing field with 400 m long furrows The soil is silty loam and can be classified by the Intake Family 0 6 The net irriga tion requirement is 100 mm The furrows have a triangular side slope of 1 1 a slope of 0 008 and a spacing of 75 cm Determine the flow rate in such a way that the application efficiency is at least 70 per cent and the cutoff time is not more than 420 minutes 1 Go to the Calculation menu and select Mode 1 Flow rate Enter the above values in the two input windows and make a run Save the results as EXAMPLE2 2 This run Table 7 6 Run 1 shows that at a flow rate of 1 21 l s this furrow can be irrigated with an application efficiency of 71 per cent A cutoff time of 587 min will then be required so the cutoff time needs to be reduced Run FURDEV in Mode 4 to see the effect when the cutoff time i
21. ion system and for testing the performance sensitivity to a change in the field parameters 7 2 Input windows When you have selected a calculation mode FURDEV will display the input screen for data entry The input data to be provided in these windows are summarised in Table 7 2 The box located in the upper left corner of the screen Figure 7 2 contains all the field parameters except infiltration Directly below is the box contain ing infiltration data The contents of these two boxes particularly those items pertaining to Geometry and Infiltration vary depending on the option select ed under the sub menu Parameters With normal usage of the program the Table 7 2 Input variables for the Furdev calculation modes Fixed flow Cutback flow Tailwater reuse Mode Mode Mode Item 1 2 3 4 1 2 83 4 1 2 3 4 Field Parameters Required depth o o oO oO o o oO o o o o0 o Max velocity o o oOo O o o 0 o o o oO o Flow resistance o o o 0 o o o0 o o o o o Slope o Oo o o o o oO o o o o o Spacing o o o o0 o o Oo o o o o o Geometry o o o o o o o o o o o o Infiltration o o o o o o oO o o o o o Input Decision Variables Inlet flow rate o o o o o o o o o Furrow length o o o o o o o Cutoff time o o o Advance ratio o o Cutback ratio o o o0 o Tailwater recovery ratio o o o o 89 FIELD PARAMETERS INPUT DECISION VARIABLES rr gt rA r m EJ 8 Wa 4 F2 Calculate or calculation mode parameters Figure 7 2 En
22. l when changing from one infiltration mode to another because the infiltration parameters for the Intake family option are not the same as those used for the other two options 7 2 2 Decision variables The decision variables in surface irrigation are normally the field dimensions furrow length and spacing the flow rate and the cutoff time It depends on the calculation mode that you have selected which of these parameters appear under the heading Decision variables see Table 7 2 Furrow length For open ended furrows there is an optimum length giving a maximum pos sible application efficiency Too long a field will result in poor performance because of a long advance time with uneven infiltration and excessive deep percolation losses in the upstream part of the field On the other hand too short a field would result in excessive surface runoff Consequently there is one length with all other variables given for open end furrows for which the sum of deep percolation and surface runoff losses is at its minimum and the application efficiency is at its maximum Flow rate For furrows the flow rate is the inflow into one furrow representing the unit flow rate per width of one furrow spacing It should not be too low otherwise the flow would not reach the end of the furrow and it should not be too high to avoid scouring In the case of open end furrows there is also an optimum flow rate similar to the furrow length where th
23. nly place in FURDEV where input data can be entered Before entering data however you have to select one of four differ ent calculation modes Table 7 1 What the first three modes have in common is that the calculated minimum infiltrated depth at the downstream end of the furrow always equals the required depth In other words no under irrigation will occur in the downstream end whereas over irrigation will always occur in the upstream part When to use the various modes is summarised below Calculation Mode 1 Flow Rate Calculation Mode 1 is primarily for design purposes when you know the length of the furrow and want to know the approximate flow rate that is need ed to achieve a reasonable performance The program will also give you the required cutoff time and the primary performance indicators as well as vari ous depth and time parameters For Fixed flow and Tailwater reuse operation modes FURDEV calculates the flow rate in such a way that the application efficiency is maximised For the Cutback flow operation mode FURDEV calculates the flow rate so that the user specified advance ratio is achieved Although the result obtained in Mode 1 is close to these targets it is advisable to continue running in Modes 3 and or 4 because in most cases refinements will still be necessary Calculation Mode 2 Furrow Length Calculation Mode 2 is the reverse of Calculation Mode 1 the flow rate is now known and you want to know the approximate
24. or closed end conditions To reduce losses and in particular runoff losses the program can be run in the operation modes Cutback flow and Tailwater reuse FURDEV does not compute how the 99 runoff water re enters the system That will be determined by local condi tions In the Tailwater reuse mode it is assumed that a certain fraction of the runoff water to be specified by the user is reused within the same fur row or in a downstream furrow In the Cutback mode it is assumed that when water reaches the end of the furrow the inflow is reduced to a value less than the inflow rate during the advance phase Before and after cut back the flow rate is constant Additional assumptions involved in the simulation of depletion and recession phases are discussed in detail in Appendix B Other general theoretical assumptions are that the infiltration can be described by the modified Kostiakov Lewis infiltration function and that the infiltration parameters have to be derived from a furrow used as infiltrometer Further the water depth at the upper boundary of the furrow can be described with Manning s equation The geometry of the cross section of the furrow triangular para bolic or trapezoidal is simulated in the program by a power law for the wet ted cross section and the wetted perimeter the upper boundary of the inflow is the maximum non erosive flow rate which can be calculated with the method developed by Hart et al 1980
25. ry file name can be confirmed or changed as described in Section 4 3 3 You can overwrite the previous file or append the current results to it Further processing of the saved results file must be done under the Files menu using View Print See Section 4 4 7 4 Error messages FURDEV usually gives an output as a result of the calculations Nevertheless some combinations of variables and parameters mostly physically unrealis tic combinations could cause mathematical problems When such problems are encountered the program terminates the calculation process and flashes a message on the screen The message typically contains two layers of infor mation the nature of the problem and suggestions on how to remedy it 97 Possible problems can be grouped into three categories general advance time problems advance time problems related only to the cutback system and cut off time problems General advance time problem The problem with the advancing front being unable to reach the downstream end of the furrow problem can be encountered with all three operation sys tems Depending on the calculation mode FURDEV will suggest increasing the flow rate and or decreasing the length of the furrow Advance time problem with cutback system In Calculation Modes 1 and 2 FURDEV calculates the required advance time as a function of the user specified advance ratio and the required intake opportunity time You can satisfy the
26. s reduced from 602 to 480 minutes 3 The results of this run Table 7 6 Run 2 show that although the applica tion efficiency has increased to 84 per cent there is under irrigation the minimum infiltrated depth is 80 mm Run FURDEV again in Mode 4 to see the effect when the flow rate is increased from 1 21 to 1 5 Vs 4 From this run Table 7 6 Run 3 you will see that there is now slight over irrigation the minimum infiltrated depth is 101 mm and the application efficiency is reduced to 69 So there is now scope to reduce the cutoff even further Run FURDEV again in Mode 4 to see the effect when the cutoff time is reduced from 480 to 420 minutes 5 Once again this run Table 7 6 Run 4 will show that there is under irri gation the minimum infiltrated depth is 89 mm while the uniformity coefficient is 95 per cent The application efficiency is 78 per cent and the distribution uniformity is 86 per cent Over the lower 117 m of the furrow the average depth infiltrated would be 5 mm less than that required The upper 283 m of the furrow would receive an average depth of 107 mm These results are acceptable Table 7 6 was also made with FURDEV Once you are familiar with the fore going basic elements of working with the program you can tackle more elab orate problems Examples are presented in Chapter 8 and concern several sets of runs with which various relationships can be established They not only illustrate the potential of FUR
27. s to calculate the application efficiency directly A ratio of 1 would be ideal but may not always be possible particularly because of the high costs involved 7 2 3 Input ranges Ranges have been fixed for all input variables as shown in Table 7 3 and are in metric units If other units are chosen in the menu the indicated ranges are converted in the program Table 7 3 Accepted ranges of input parameters Accepted values Input parameters Field Parameters Required depth Dreq 25 250 mm Maximum velocity 7 15 m min Flow resistance n 0 01 0 08 Furrow slope So 0 0003 0 03 m m Furrow spacing Ws 0 5 1 5 m Side slope z 0 5 3 0 m m Intake family 0 05 2 0 Infiltration coefficient k Infiltration exponent A Infiltration constant fs Input Decision Variables 0 050 30 mm min 0 01 0 7 0 005 10 mm min Furrow length L 5 700 m Flow rate Q 0 02 16 67 l s Cutback ratio 0 65 1 00 Advance ratio 0 1 0 9 Tailwater reuse ratio 0 1 1 0 Cutoff time Teo 10 2000 min 94 Based on a large number of runs the ranges have been fixed in a bid to avoid too many impossible combinations and corresponding error messages For all practical purposes the ranges of the individual parameters will be more than sufficient If you combine extreme values of the individual param eters you may not get a result FURDEV will then flash you a message on the screen indicating how to change these values
28. tering system parameters in Furdev values of the field parameters will be given once for a particular situation and will be changed only to make sensitivity analyses after satisfyi ng results have been obtained in Mode 3 or 4 Detailed examples can be found in Chapter 8 Section 3 2 The decision variables are displayed in the box located at the upper right cor ner of the input screen The data to be entered here depends on the selected Calculation mode and the selected Operation mode 7 2 1 Field parameters Required depth The required depth to be infiltrated at the end of the furrow is the first input in the Field Parameters window This target depth is determined outside FURDEYV as was indicated in Chapter 3 Section 1 3 Non erosive velocity The flow velocity in the furrow should not exceed a maximum non erodible value which depends on the soil type It is usually taken at about 8 m min in erosive silty soils and up to about 13 m min in more stable clay and sand soils see Section 3 1 4 This maximum occurs in the first part of the furrow Flow resistance Fangmeier and Ramsey 1978 when investigating furrow infiltration found values ranging between 0 02 and 0 04 SCS USDA 1983 states that a flow resistance of 0 04 is appropriate for furrows No further details are given In 90 contrast to basin and border irrigation there are no crops in the furrow con sequently the range of n values is smaller Walker 1989 uses
29. this n 0 04 in all calculation examples See also Section 3 1 2 Field slope The field slope of graded furrows should neither be too high to avoid erosion nor too low which would result in a slow advance For furrows suitable slopes normally vary between 0 05 and 1 per cent Small furrows and corrugations however can be used on steeper slopes up to 2 per cent Furrow spacing The furrow spacing is a dual purpose parameter In the first Slats it is a field dimension which is primarily used to convert volumes to depths But it is also used for modelling the infiltration process where the furrow spacing is used to convert the A k and f values corresponding to the modified SCS intake families The input value should not conflict with the given furrow geometry Just suppose that you have specified a trapezoidal section with 1 5 1 side slope and 0 1 m bed width Suppose also that in your field the depth of the furrows is 20 cm and the top width of the ridges is 25 cm The actual spacing should then be equal to 12 54 30 104 30 12 5 95 cm Furrow geometry Under this menu there are two sub options Cross sectional type and Sigma amp tau The second option refers to the parameters 01 02 T and Tz that are used in the program to specify the furrow cross section For details see Appendix B Because most users would not know which value to give here and calcu lating the parameters could be a tiresome job the program offers the easier
30. uniformity o O o O Uniformity coefficient o o o o Time variables Advance time o o o o Depletion time O o O o Recession time o o o o Intake opportunity time o O o o Infiltrated depths Maximum infiltrated depth O o O o Minimum infiltrated depth o o o Average infiltrated depth o o o o Surface runoff o o o o Over irrigation o Under irrigation o Length of over irrigation o Length of under irrigation o 96 530 T 2 6 SGOT ee 265 5 T 132 a 0 75 150 225 distance m 330 depth mm over irrigation under irrigation Figure 7 4 Advance curves recession curves and infiltration profiles in Furdev operation mode Tailwater reuse For the operation mode Cutback flow how ever and for all calculation modes the cutback flow rate is added to the out put variables in Modes 3 and 4 the advance ratio is added as well By pressing F3 you will see two graphs showing the main results the upper one shows advance and recession times in relation to furrow distance while the lower one shows the infiltrated depths along the furrow length Under and over irrigation are indicated where applicable This graph can be saved with F8 or F9 Figure 7 4 shows a graph of the results of Run 3 from Example 1 see Table 7 5 Note here the recession time is depicted and not the cutoff time as with BASDEV The tabulated simulation results can be saved together with the input data with F4 In a small window the path directo
31. will have to decide whether you find the high velocity acceptable or not 7 5 Assumptions and limitations The FURDEV program is based on the volume balance method which is explained in detail in Appendix B The main difference between furrows and basins or borders is that the geometry of their cross sections is different and that therefore the infiltration process and the flow process also differ In basins and borders it is generally assumed that the infiltration is one dimen sional in the vertical downward direction whereas in furrows water infil trates over the entire wetted perimeter in the furrow and should therefore be characterised as a two dimensional process The volume balance method calculates the propagation of the wetting front along the furrow during the advance phase Algebraic equations are used to simulate the pounding depletion and rec ssion phases Implicit assumptions for the modelling of the advance phase are as follows The furrow slope is greater than zero The field can have a minor cross slope as long as the slope in the furrow is constant The cutoff time is always greater than the advance time This limitation is introduced to make sure that advance and recession do not occur simulta neously a situation that the volume balance model cannot handle During the advance time the inflow is constant The furrow is free draining at the end FURDEV is not able to calculate the advance and recession curve f
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