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PONDS Version 2.26 Users Manual.

1. 5 10 Table 5 5 Example Problems for Retention Pond Recovery Refined Method 5 13 Table 5 6 Summary of Regulatory Criteria for Defining Drawdown Impact Distance 5 15 Table 5 7 Recommendations for Selecting Aquifer Parameters for Dewatering Analysis 5 17 Table 5 8 Input Data amp Results Postdevelopment Runoff Parameters 5 18 Table 5 9 Input Data amp Computation Water Quality Volume 5 18 Table 5 10 Input Data Pond Dimensional Parameters 5 19 Table 5 11 Stage Versus Area Data for Retention Pond _ 5 19 Table 5 12 Input Data Discharge lt 5 20 Table 5 13 Input Data Aquifer 5 20 Table 5 14 Input Data Ditch Dewatering Example 5 21 Table 5 15 Summary of Key Results for Examples 43 1 43 9 5 22 Figure 4 1 Figure 5 1 Figure 5 2 Figure 6 1 Figure 7 1 Figure 8 1 Figure 9 1 LIST OF FIGURES excluding appendices Simplified Retention Pond Recovery Analysis Model 4 1 Retention Pond Recovery 5 1 Hydrostratigraphic Variations for Ditch Dewatering Impacts
2. RD e Ue Reden 1 1 1 1 REVIEW OF LICENSE AGREEMENT 555 1 1 1 2 HARDWARE REQUIREMENTS 1 1 1 3 PROGRAM INSTALLATION leeeeeeeee hh rn 1 1 1 4 PROGRAM SECURITY 444 Mowat EE VA E SES A ae SY Un 1 2 1 5 PROGRAM EXECUTION eek n RE ey nem ag po let e 1 2 1 6 COMMON PROBLEMS 4 iur enu RU URS RUNS E Ere RIS ESI rn 1 2 1 6 1 Hardware ese Ete ais i e ce eR wate wise UG Re Ute siut 1 2 1 6 2 install Problems s enr hh mem xm Rex rmx en enn 1 3 1 6 3 Copy Protection Problems 1 3 1 6 4 Missing Inadvertently Deleted Files Problem 1 3 2 OVERVIEW OF STORMWATER MANAGEMENT SYSTEMS 2 1 2 1 GENERAL EDU 2 1 2 2 DESCRIPTION OF SYSTEMS e 2 1 2 2 1 Retention Systems 2 1 2 23 2 Wet Detention Ponds 2 1 2 2 3 Filtration Systems owe eel ea IERI dae ache eels 2 2 2 2 3 1 Side bank and Pond bottom Filters 2 2 2 2 3 2 Vertical Hollow Cylindrical Sand Filter aka VVRS 2 2 2 2 4 Underdrain 2 3 2 2 5 Exfiltration Trench eee e aye a rhe face Ware Severe RR E
3. August 7 1995 PONDS USER MANUAL 5 13 3 Results 5 24 Detailed results of each of the above simulations can be viewed on the interactive output screen or can be printed out from the data files on disk Key results for all examples are summarized in Table 5 15 Table 5 15 Summary of Key Results for Examples 3 1 to 43 9 EXAMPLE 3 1a 3 1b 3 2 3 3 3 4 3 5 APPLICATION Generate runoff hydrograph for 25 yr 24 hr storm event Route the hydrograph generated in 3 1a through a dry bottom retention pond which has multiple discharge structures an overflow weir amp a bleeddown pipe taking infiltration credit into account during the routing Same as Example 3 1b without infiltration credit Same as Example 3 1b without discharge structures i e a closed pond Note that closed ponds are usually designed for a 100 yr 24 hr storm event but the 25 yr 24 hr hydrograph is used here for expediency Same as Example 3 1b without discharge structures and infiltration credit This is a worst case situation Recovery of water quality volume for dry bottom pond in Example 3 1b excluding unsaturated infiltration RESULTS see Table 5 8 amp data file on disk SWFWMD HYD peak stage 102 82 ft peak discharge rate 15 47 cfs peak stage 102 99 ft peak discharge rate 20 52 cfs peak stage 104 92 ft cumulative volume infiltrated 14 days after storm 134 511 ft3
4. Base of uppermost aquifer Horizontal saturated hydraulic conductivity when using ground infiltration credit Note use k 0 001 ft day when not considering infiltration credit Fillable porosity of aquifer Seasonal High Water Table for dry retention pond example Seasonal High Water Table for wet bottom pond example appen mearan ft MSL 100 5 August 7 1995 PONDS USER MANUAL 5 23 Table 5 14 Input Data Ditch Dewatering Example PARAMETER DESCRIPTION MAGNITUDE DITCH DIMENSIONAL PARAMETERS Length of ditch ft 500 Width of ditch ft 10 Side slopes assumed vertical DISCHARGE STRUCTURE PARAMETERS ditch control level is modeled using an equivalent sharp crested weir which is as wide as the ditch Weir discharge elevation 92 0 for Case 1 ft MSL 97 1 for Case 2 Weir discharge coefficient 3 13 Weir length ft 10 Weir discharge exponent 1 5 A 88 0 for Case 1 Base of uppermost aguifer ft MSL see Figure 4 for Case 1 and Case 2 97 0 for Case 2 Initial water table elevation ft MSL 96 0 for Case 1 4 99 0 for Case 2 Horizontal saturated hydraulic conductivity ft day 10 Drainable porosity of aquifer 96 20 TIME STEP SIMULATION PARAMETERS Computational time step hr 100 Duration of simulation hr 2160 or 90 days AQUIFER PARAMETERS
5. to U P jump discontinuities may appear in the reported water elevation This should not be misinterpreted as a problem or an error As mentioned previously the model uses a different algorithm which is uncoupled from MODFLOW to simulate the unsaturated flow regime prior to saturated lateral flow Although volume is preserved during the transition the model may not report a continuous water level at the transitional time step Note that the program models discharge through the overflow structures if there are any for any flow type August 7 1995 PONDS USER MANUAL 5 12 August 7 1995 PONDS USER MANUAL 5 13 5 12 EXPLANATION OF CERTAIN ASPECTS OF THE PROGRAM The following are common oversights made by users when running the model for the first time The fillable porosity parameter must be entered in percent not decimals So for example input 2596 and not 0 25 If manually inputting a hydrograph a value must be entered for the outside recharge rate typically 0 in order for the program to recognize it as a valid line PONDS requires input of stage area data There is no explicit pond bottom elevation parameter The first stage in the stage vs area data represents the pond bottom elevation If the water table is above the first stage elevation the water table elevation is automatically set as the elevation where there is zero accumulated storage volume In situations where the water table is deep and whe
6. Case i Control Base of Hydraulic fer to Fig 5 2 Objective A ads refer to Fig Elevation Aquifer Conductivity 1 compute water table ditch control base of k of uppermost drawdown amp seepage elevation uppermost aquifer rates into ditch aquifer 2 compute water table 0 1 ft above base of base of k of uppermost drawdown amp seepage uppermost aquifer uppermost aquifer rates into ditch aquifer 3 compute water table 0 1 ft above base of base of k of uppermost drawdown uppermost aquifer uppermost aquifer aquifer 3 compute seepage rates ditch control base of weighted into ditch elevation lower average k of aquifer saturated thickness The criteria in Table 5 7 apply equally well when modeling the effects of an adjacent ditch on retention pond recovery 5 13 2 Input Parameters 9 15 1 Examples 23 1 through 43 8 A common set of input data is used for Examples 3 1 through 43 8 These data are presented in Tables 5 8 through 5 13 which are self explanatory 2113 223 Example 43 9 The objective of this example is to determine the impact distance from a ditch for establishing wetland setbacks etc Table 5 14 contains the input parameters used for the 500 ft long ditch in this example Figure 5 2 shows the three typical cases encountered and Table 5 7 summarizes how the aquifer parameters should be selected for these cases Data files for cases 1 and 2 are included on the disk Although not included here case 3
7. August 7 1995 PONDS USER MANUAL 1 6 Table 1 1 List of Files File Name Description EXAMPLE1 DAT EXAMPLE2 DAT EXAMPLE3 DAT EXAMPLE4 DAT EXAMPLE5 DAT EXAMPLE6 DAT EXAMPLE7 DAT EXAMPLE8 DAT EXAMPLE9 DAT EXAMPL10 DAT EXAMPLES INP EXAMPLE3 HYD Data files for Example Problems presented in the User Manual Note that data files for example problems for the Retention Pond Recovery Refined Method module are listed below These files are located in the main program PONDS226 directory SWFWMD HYD SWFWMD INP SWFWMD1 DAT SWFWMD2 DAT SWFWMD3 DAT SWFWMD4 DAT SWFWMD5 DAT SWFWMD6 DAT SWFWMD7 DAT SWFWMD8 DAT SWFWMD9 DAT SWFWMD10 DAT SWFWMD11 DAT Data files for example problems for the Retention Pond Recovery Refined Method module These files are located in the main program PONDS226 directory CONTINUED ON NEXT PAGE August 7 1995 PONDS USER MANUAL 1 7 Table 1 1 List of Files File Name Description BJ200 BGI Printer Graphic Drivers _BJC600 BGI CANON BGI _DJ BGI These files are located in the PONDS226 GRAPHICS _DJC BGI subdirectory _DJC550 BGI FX BGI _GENERIC BGI HGL2 BGI _HP7470 BGI _HP7475 BGI _HP7550 BGI HP7585 BGI _IBMQ BGI _LJ3R BGI _Lj4 BGI PJ BGI PP24 BGI PS BGI EGAVGA BGI VGA Screen Driver These files are located in the PONDS226 GRAPHICS subdirectory BOLD CHR Borland Stroke Fonts EURO CHR GOTH CHR These files are locat
8. Page Description Explanation Each line of data contains 3 parameters elapsed time hr runoff rate cfs and recharge rate to the water table outside the limits of the pond nilow Hydrosraphs ft day Except for complex simulations involving fluctuation of the water table the recharge rate parameter should be set to zero This is the simulation time after the storm event to model recovery Simulation Time of the pond 5 3 MODEL LIMITATIONS The user should also appreciate the following limitations of this module Surface water discharge is only modeled for free unsubmerged discharge structures such as weirs orifices and V notches Up to 3 discharge structures can be modeled for a single pond If the ditch feature is used symmetry is implicit since the model assumes that there is a mirror image of the ditch on the other side of the pond 5 4 SUPPLEMENTAL FUNCTION KEYS Apart from the standard function keys see page 3 6 the user should be aware of the supplemental function keys listed in Table 5 2 August 7 1995 PONDS USER MANUAL 5 5 Table 5 2 Special Function Keys for Refined Recovery Analysis Module DESCRIPTION Pond aquifer parameters SPECIAL FUNCTION KEYS F3 shows additional function keys lt F11 gt exports results to an ASCII text file lt F12 gt exports time vs infiltration data for use as an offsite hydrograph in AdICPR Adjacent ditch data F1
9. With typical water table gradients of 25 the assumption that the initial water table is flat is not an oversimplification when one considers that the radius of influence is usually less than 500 feet or so The heads in all cells except at the boundaries are free to vary during the transient simulation Within the pond however drain cells are used to constrain the maximum level at the specified control elevation Stress Periods The total simulation time or time specified for the water table rise to occur is divided into six equal stress periods for computational accuracy For additional numerical precision the last sixth stress period is divided into 10 time steps August 7 1995 PONDS USER MANUAL A 4 August 7 1995 PONDS USER MANUAL A 5 Recharge amp Drains Recharge to the surficial aquifer is used to simulate the rise of the water table The recharge rate is assumed to apply uniformly during the length of the loading period and its magnitude is selected to produce the input rise in the water table factoring in the specific yield or fillable porosity of the aquifer Within the pond recharge is used to model a simultaneous rise of the pond water level with the aquifer water table up to the pond control level beyond which the pond is controlled at its control level for the remainder of the simulation using the MODFLOW DRAIN module to represent the pond cells The summation of the discharge rates from the drains for
10. rainfall recharge in the uppermost aquifer during the wet season or some other design event such as a 25year 24 hour storm As the water table rises during the wet season and reaches the control elevation in the pond the dewatering effect causes a lowering of the water table adjacent to the pond or ditch underdrain borrow pit etc and the cone of depression spreads laterally with time and with the rate of recharge outside the pond The most critical case is at the end of the wet season or at the end of the study period when the the water table peaks following a design storm event APPROACH amp METHODOLOGY For computational purposes the hydrostratigraphy is characterized as a 1 layered unconfined aquifer system which is characterized based on site specific data usually contained in the project geotechnical report The computer model chosen for the analysis of the dewatering due to the pond is titled A Modular Three Dimensional Finite Difference Groundwater Flow Model by McDonald and Harbaugh 1984 U S Geological Survey This model simulates ground water flow in three dimensions by writing a Taylor expansion for the system of second order partial differential equations governing steady state or transient flow through porous media A transient simulation is appropriately utilized in the simulation of the dewatering August 7 1995 PONDS USER MANUAL A 3 Model Grid The areal extent of the model subdomain for this analysis or
11. 5 16 Conceptual Model For Ground Water Baseflow 6 1 Filtration System Idealization 7 1 Conceptual Model of Vertical Hollow Cylindrical Filter 8 1 Conceptual Model of Underdrain System 9 1 TABLE OF CONTENTS continued August 7 1995 Appendix A Appendix B Appendix C Appendix D Appendix E Appendix F LIST OF APPENDICES Methodology For Estimating Ground Water Baseflows Into Ponds Theory For Analysis of Pond Recovery Using Side Bank or Pond Bottom Filters Simplified Analytical Method for Recovery Analysis of Dry or Wet Bottom Retention Ponds Theory for Recovery Analysis of Dry or Wet Bottom Retention Ponds During amp Following Transient Hydraulic Loading Methodology for Recovery Analysis of Underdrained Retention Ponds Recovery Analysis of Ponds with Vertical Hollow Cylindrical Sand Filters August 7 1995 PONDS LICENSE AGREEMENT Page 1 of 3 PONDS PROGRAM LICENSE AGREEMENT IMPORTANT YOU SHOULD CAREFULLY READ THE FOLLOWING TERMS AND CONDITIONS BEFORE OPENING THIS DISKETTE PACKAGE OPENING THIS DISKETTE PACKAGE INDICATES YOUR ACCEPTANCE OF THESE TERMS AND CONDITIONS IF YOU DO NOT AGREE WITH THEM YOU SHOULD PROMPTLY RETURN THE UNOPENDED PACKAGE UPON RECEIPT OF THE PACKAGE BY DEVO SEEEREERAM YOUR ORDER WILL BE CANCELLED AND MONEY PAID BY YOU WILL BE REFUNDED Devo Se
12. and post processor to these calculation routines The following is a list of the key features of this module Although the current version of the program can only simulate single pond at a time it can perform multiple interconnected pond routing analysis if it is run in conjunction with adICPR August 7 1995 PONDS USER MANUAL 3 3 A maximum of 3 discharge structures per pond can be modeled The types of discharge structures which may be modeled include unsubmerged weirs orifices notches etc and other free discharge structures It is a true routing model with or without infiltration credit and can predict peak flow rates and stage elevations since it models the true stage area storage relationship of the pond Hydrographs generated using adICPR can be imported directly into the program and the ground water discharge versus time data rating curve can be subsequently exported for use in adICPR This is also possible for multiple ponds In addition to reading hydrographs created using AdICPR or the SWFWMD hydrograph generation routine included with PONDS i e Module 3 hydrographs can be input manually in a spreadsheet type environment or can be read from ASCII data files a The program has the flexibility to simulate complex fluctuations of the water table outside the pond during the storm event The program can simulate the effects of adjacent ditches with control levels above or below the ambi
13. improper calculation of the pond length and width The equations for computing the equivalent pond length and width is described next August 7 1995 PONDS USER MANUAL 4 3 4 3 CALCULATION OF EQUIVALENT POND WIDTH amp LENGTH All of the idealizations assume a rectangular plan configuration for computational purposes If you are dealing with a pond of irregular shape or non rectangular shape a methodology is suggested below for determining an equivalent pond length and equivalent pond width In selecting an equivalent pond length and width two criteria must be satisfied i the pond stage height h at the overflow i e discharge elevation minus pond bottom elevation multiplied by the equivalent pond length L and equivalent pond width W must give the storage volume V from the stage storage data Mathematically this may be stated as follows hxLxW y 1 Note that if we are dealing with a wet bottom pond h is the discharge elevation minus the initial water table elevation For dry bottom ponds h is the discharge elevation minus the pond bottom elevation The volume V is the volume between the discharge elevation and the discharge elevation minus h CONTINUED ON NEXT PAGE August 7 1995 PONDS USER MANUAL 4 4 ii The effective perimeter of the pond P must be equal to the perimeter of the equivalent rectangle i e 2L 2W In mathematical terms QxL QxW P 2 Note that P is the effective
14. side bank or pond bottom filter Ground water baseflow is computed using the previously described module which can also be accessed as a subprogram from the filtration sizing menu 3 2 6 Module 6 Vertical Volume Recovery Filtration Structures aka VVRSs This module computes the number of Vertical Hollow Cylindrical Sand Filters also known as Vertical Volume Recovery Structures or VVRS required for recovery of the treatment volume The theory for this recovery analysis was developed by the author and is described in Appendix F of this manual This module also automatically allows for ground water baseflow in the calculations August 7 1995 PONDS USER MANUAL 3 5 3 2 7 Module 7 Underdrain Design Calculations This module determines the spacing total length and diameter of subsurface drains for Underdrained Retention Ponds a relatively new but increasingly popular Best Management Practice permitted by SJRWMD The methodology is described in Appendix E and is based on design procedures outlined in the book Drainage of Agricultural Land A Practical Handbook For the Planning Design Construction and Maintenance of Agricultural Drainage Systems by the Soil Conservation Service of the USDA Ground water baseflow is automatically included in design calculations Ground water baseflow is computed using the previously described module which can also be accessed as a subprogram from the underdrain menu In addition to the above th
15. the terminus and b at every 400 feet or every bend of 45 or more degrees whichever is shorter 7 Underdrain basin should be stabilized with permanent vegetative cover August 7 1995 APPENDIX F THEORY FOR RECOVERY ANALYSIS OF RETENTION PONDS USING VERTICAL HOLLOW CYLINDRICAL SAND FILTERS aka VVRS August 7 1995 PONDS USER MANUAL F 1 RECOVERY ANALYSIS OF PONDS WITH VERTICAL HOLLOW CYLINDRICAL SAND FILTERS aka VVRS by Devo Seereeram Ph D P E ABSTRACT Vertical hollow cylindrical sand filters are used to filter and then discharge stormwater retained in stormwater management ponds They are known commercially as Vertical Volume Recovery Structures or VVRS and are preferred as an alternative to conventional pond side bank filters since they require less maintenance Stormwater regulations in the state of Florida specify the time period in which the treatment volume must be filtered from the pond to ensure that storage volume is available to accomodate runoff from the next storm Typical regulations in Florida call for retaining the first 1 to 3 inches of stormwater runoff depending on the sensitivity of the receiving water body and filtering this retained runoff volume within 3 days This paper presents theoretical equations for estimating the number of vertical hollow cylindrical sand filters or VVRS required for recovery of the stormwater treatment volume ina prescribed time period The derivation leads directl
16. 3 1b excluding unsaturated infiltration Recovery of water quality volume for dry bottom pond in Example 3 1b including unsaturated infiltration 3 1b 3 2 3 3 3 4 3 5 3 6 Recovery of water quality volume for wet bottom wet detention pond with bleed down device Same as Example 3 1b but higher water table Take into account infiltration during recovery Recovery of water quality volume for wet bottom wet detention pond with bleed down device Same as Example 3 1b but higher water table Do not take into account infiltration during recovery Dewatering due to ditching Cases 1 and 2 on Figure 5 2 RESULTS time vs inflow rate peak stage FILE NAME SWFWMD INP peak discharge rate peak stage peak discharge rate peak stage volume available in pond 14 days after storm peak stage peak stage volumes recovered after 36 hr and 72 hr peak stage SWFWMD3 DAT volumes recovered after 36 hr and 72 hr volumes recovered after 24 hr 48 hr 60 hr and 120 hr volumes recovered after 24 hr 48 hr 60 hr and 120 hr Water table drawdown SWFWMD HYD SWFWMD1 DAT SWFWMD2 DAT SWFWMD4 DAT SWFWMD5 DAT SWFWMD6 DAT SWFWMD7 DAT SWFWMD8 DAT SWFWMD10 DAT SWFWMD11 DAT August 7 1995 PONDS USER MANUAL 5 16 Dg f Example 32 Example 3 2 is the same run as Example 3 1b but without the infiltration credit The infiltration
17. 36 300 August 7 1995 PONDS USER MANUAL 5 21 Table 5 10 Input Data Pond Dimensional Parameters PARAMETER DESCRIPTION UNIT MAGNITUDE Equivalent Pond Length ft 270 Equivalent Pond Width ft 120 Stage vs Area data see Table 5 11 Maximum Area Available for Unsaturated Infiltration ft 32 400 Table 5 11 Stage Versus Area Data for Retention Pond Stage Area Cum Volume Remarks ft NGVD ft ft 26 130 2 10 226 27 281 0 20 908 101 6 29 643 8 43 674 4H 1V up to within limits of pond 32 400 0 71 588 then 10H 1V 35 584 0 85 185 38 896 0 100 081 42 336 0 116 327 top of pond 104 1 45 904 0 133 975 104 5 153 076 104 9 53 424 0 173 681 outside limits of pond 105 3 195 841 105 7 61 456 0 219 607 August 7 1995 PONDS USER MANUAL Table 5 12 Input Data Discharge Structures 5 22 PARAMETER DESCRIPTION UNIT MAGNITUDE Discharge Structure 1 Sharp Crested Overflow Weir Weir Discharge Elevation ft MSL 102 0 Weir Discharge Coefficient 3 13 Weir Length ft 7 Weir Exponent 1 5 Discharge Structure 2 Bleed down pipe sharp edged orifice Table 5 13 Input Data Aquifer Parameters PARAMETER DESCRIPTION Unsaturated vertical infiltration rate Orifice Control Elevation ft MSL 100 5 Orifice Discharge Coefficient 4 9 Orifice Diameter inch 3 Orifice Area ft 0 0491 Orifice Exponent 0 5 UNIT MAGNITUDE
18. ANALYSIS OF RETENTION POND WITH VVRS FILTERS contained in data file EXAMPLE8 DAT The objective of this problem is to calculate the number of VVRS filters required for the pond described in Example 7 Recall that in Example 7 1227 lineal feet of side bank filter was computed as the minimum requirement The typical VVRS for this pond will be embedded 3 feet below the pond bottom and will have a positive outfall with the same tailwater elevation as the side bank filter i e 0 9 ft below the pond bottom Note that the bottom elevation of the treatment volume is computed from equation A 7 in Appendix B Assume that the pond bottom is at an arbitrary elevation datum of 0 0 ft The hydraulic conductivity of the VVRS filter media is 200 feet day Pond amp Stormwater Volume Parameters Treatment volume V cubic feet 340 000 ft Top elevation of treatment volume TOP ft datum 4 0 ft datum Bottom elevation of treatment volume BOT ft datum 0 217 ft datum Tailwater or invert elevation TWL ft datum 0 9 ft datum VVRS Details Inside diameter of VVRS structure Din ft 2 feet Outside diameter of VVRS structure Dout ft 6 feet Elevation of top of concrete base BASE ft datum 3 0 ft datum Hydraulic conductivity of filter media k ft day 200 ft day Design Criteria Recovery Time T day 3 days Factor of Safety FS dimensionless 2 Background Seepage Ground water baseflow into pond qb gpm 20 22 gpm As noted on the output o
19. Infiltrator chambers increase the storage available in the trench and promotes a more uniform distribution of recharge within the trench Generally exfiltration trenches are used where space is limited and or land costs are relatively high However the operational life of an exfiltration trench is believed to be short possibly 5 to 10 years because of sediment accumulation and clogging by fines These systems if not properly designed may therefore require extensive maintenance or complete replacement during the design life of the system 2 2 6 Swales Swales are man made or natural systems shaped or graded to specified dimensions and designed for the conveyance and rapid infiltration of stormwater runoff Unlike retention ponds swales are open conveyance systems in that there are no physical barriers such as berms or check dams to impound the runoff in the swale prior to discharge to the receiving water Swales are designed to infiltrate a defined quantity of runoff through the permeable soils of the swale floor and the side slopes into the shallow ground water aquifer The swale holds water only during and immediately after a storm event and thus the system is normally dry August 7 1995 PONDS USER MANUAL 2 4 2 2 7 Wetlands Stormwater Management System The wetlands stormwater management system design and performance criteria in the stormwater rule are an initial step by SJRWMD in a field where limited knowledge exists Only wetlands
20. User Specified Rainfall Distribution amp Unit Hydrograph The user may create a customized dimensionless rainfall distribution file using an ASCII text editor This file must be called USER RAI and must be in the following free format Line 1 N number of x y pairs in dimensionless rainfall distribution file Line 2 X y Line 3 X3 yj Line 4 X3 Line 1 YN Note x Elapsed Time Duration of Storm Event Fraction of total rainfall for storm event This user defined rainfall distribution may be used in the hydrograph generation routine by selecting the last of the the rainfall distribution options The USER RAI file must be in the program directory with the other RAI files so it can be accessed by PONDS Similarly the user may also create a customized dimensionless unit hydrograph file using an ASCII text editor This file must be called USER UHG and must be in the following free format August 7 1995 PONDS USER MANUAL 5 9 Line 1 Hydrograph shape factor Line 2 n number of x y pairs in dimensionless unit hydrograph file Line 3 X Line 4 Xj Line 5 X Line n 2 x Yn Note x Elapsed Time Time to peak y Runoff rate peak runoff rate This user defined normalized unit hydrograph may be used in the hydrograph generation routine by selecting the last of the the unit hydrograph or shape factor options The file USER UHG must be in the program directory with t
21. as a laterally infinite single layered homogenous isotropic water table aquifer of uniform thickness with a horizontal pre loading phreatic surface The three dimensional shape of the pond is assumed to be that of a rectangular trench The pond fills up suddenly with the treatment volume i e a slug loading This assumption is consistent with SIRWMD criteria which does not allow for ground water or surface water discharge during the storm event The moving zone of saturation or transitory ground water mound is idealized as a series of triangular prisms adjacent to the pond perimeter At the corners of the rectangular pond the triangular prisms assume the shape of a quadrant of a solid cone The lateral extent of the mound or radius of influence increases as recovery progresses From the law of conservation of mass the volume of water which infiltrates out of the pond trench is equal to the volume of water in soil storage in the triangular saturated prism at any instant Darcy s Law is the governing equation for saturated ground water flow Dupuit Forchheimer assumptions are applicable i e 1 Flow is considered to be purely horizontal 2 Flow is assumed to be uniformly distributed with depth The Dupuit Forchheimer theory loses accuracy if the depth of the impermeable layer increases because of the increased importance of vertical flow Bouwer 1969 found that the Dupuit Forchheimer theory gave reasonable results if the di
22. credit is turned off during the routing by setting the permeability aka hydraulic conductivity of the soil to a relatively low magnitude such as 0 001 ft day This allows the design engineer or the permit reviewer to assess the worst case stage and discharge rate if the pond silted up or if the input permeability value is higher than a representative value for the aquifer 5 13 14 Example 43 3 Example 3 3 is for a pond without a postive outfall i e a closed pond This example is the same as Example 3 1b but with both discharge structures turned off and the inclusion of a recovery period i e simulation time of 14 days after the storm The objectives of this example are to determine the peak stage during the storm and the cumulative volume infiltrated up to 14 days following the storm Note that some agencies require closed ponds to be able to accomodate a second design storm 14 days following the first one 5 13 1 8 Example 3 4 Example 3 4 is the same as the previous example i e Example 3 3 but with no infiltration credit Like Example 3 2 infiltration credit is deactivated by reducing the aquifer permeability to a small value such as 0 001 ft day or less Such an analysis is useful for predicting a worst case stage during the storm if the design engineer reviewer suspects the aquifer permeability might be over estimated or if pond bottom siltation is likely 5 13 1 6 Examples 43 5 amp 426 Example 3 5 models the recov
23. el axe eR IURIS CET ER QUESTION NM CR d see Appendix B Example Problems io one kate aste Nea epe qe RUE ORO na Arar eee as pp 7 3 Figure 7 1 Filtration System Idealization August 7 1995 PONDS USER MANUAL 7 2 7 2 LIST OF INPUT PARAMETERS 1 Hydraulic conductivity of filter media K 2 Surface area of pool at top of volume to be filtered A 3 Surface area of pool where last increment of water drains through filter 4 Driving head when water stage in pond at top of volume to be filtered h 5 Driving head when last increment of water enters filter hpo 6 Side slope of pond S 7 Dimensions of sand filter X L as shown on Figure 7 1 8 Percent of volume between A and A to be filtered 9 Background seepage amp other baseflows into pond if any This is estimated from the Background seepage module Note that the filter detail shown on Figure 7 1 utilizes a gravel envelope around the drain pipe since it is hydraulically much more efficient than completely surrounding the pipe with the sand filter media August 7 1995 PONDS USER MANUAL 7 3 7 3 EXAMPLE 7 FILTRATION SYSTEM WITH BASEFLOWS contained in data file EXAMPLE7 DAT Assume that the pond in example 4 uses a side bank filtration system for treatment of the water quality volume The roadway underdrain system of example 6 is also assumed to be connected to the pond The objective of this example is to determine the length of f
24. elevation 24 89 ft The radius of influence is 39 28 feet August 7 1995 PONDS USER MANUAL 4 8 EXHIBIT 2 PRINTOUT OF EXAMPLE PROBLEM 2 August 7 1995 MODULES 2 amp 3 RETENTION POND RECOVERY ANALYSIS REFINED METHOD INPUT PARAMETERS amp EXAMPLE PROBLEM August 7 1995 PONDS USER MANUAL 5 1 5 RETENTION POND RECOVERY ANALYSIS REFINED METHOD 5 1 CONCEPTUAL MODEL Conceptual model see Figure 5 1 below Theory vod ACER UR OR AUR a a RN see Appendix D Figure 5 1 Retention Pond Recovery Model Refined Method August 7 1995 PONDS USER MANUAL 5 2 5 2 LIST OF INPUT PARAMETERS Input parameters for this model are summarized in Table 5 1 Table 5 1 List of Input Parameters Input Parameter Page Description Explanation Equivalent Pond Length Equivalent Pond Width Base of aquifer These parameters control the effective perimeter of the pond through which saturated flow can occur See the illustration at the bottom of page 4 4 for the physical meaning of the effective perimeter parameter Note that the length and width do not control the stage vs area relationship of the pond as this data must be explicitly input These aquifer parameters should be obtained from the site specific elevation geotechnical report See page 3 7 of this manual Guidance for selecting these parameters is provided in Chapter 7 of the a SJRWMD p
25. flow type is printed in the last column of the tabular output Table 5 4 Symbols amp Description of Flow Types Flow Type Description U Discharge to ground water is via vertical unsaturated flow through the bottom of the basin The unsaturated infiltration flow rate changes depending on the stage in the pond and the pond s stage area characteristics This flow type means that there is still storage in the soil voids beneath the pond but the inflow rate is not rapid enough to cause perching of the water in the pond U P Discharge to ground water is via vertical unsaturated flow through the bottom of the basin Although the storage in the soil voids beneath the pond has not been filled the inflow rate in cfs is larger than the unsaturated infiltration rate in cfs which results in perching of water in the pond U S There is usually only one computational time step which has this flow type It is the time step where the soil voids beneath the pond become filled and the flow mechanism transitions from unsaturated flow to saturated flow S Ground water discharge is saturated lateral flow computed using MODFLOW Once the model transitions to saturated flow it cannot transition back to unsaturated flow If there is water in the pond the program reports the water level in the pond On the other hand if there is no water in the pond the program reports the ground water level Therefore as the flow type changes from
26. high water table elevation within pond footprint ft datum or feet below land surface Fluctuation rise of the water table during a normal wet season feet and duration of normal wet season days August 7 1995 MODULE 1 RETENTION POND RECOVERY ANALYSIS SIMPLIFIED METHOD INPUT PARAMETERS amp EXAMPLE PROBLEMS August 7 1995 PONDS USER MANUAL 4 1 4 RETENTION POND RECOVERY ANALYSIS SIMPLIFIED METHOD 41 GENERAL Conceptual model 2 ur ex e RC C C anal see Figure 4 1 below Description of input parameters see page 4 2 Theory eos ot el axe IER S IURIS CRT ewes Catenin OUR see Appendix C Example Problems sk ss kamin a ee En Nea i ay BRS pp 4 5 through 4 8 Figure 4 1 Simplified Retention Pond Recovery Analysis Model August 7 1995 PONDS USER MANUAL 4 2 4 2 LIST OF INPUT PARAMETERS 1 Equivalent Pond Length L 2 Equivalent Pond Width W 3 Pond Bottom Elevation PB 4 Porosity of Material Within Pond p in 96 5 Base of aquifer elevation B 6 Seasonal high water table elevation WT 7 Horizontal hydraulic conductivity of aquifer Kh 8 Fillable porosity of aquifer n 9 Unsaturated vertical infiltration rate Iv 10 Runoff volume V 11 Percent of runoff volume to be recovered PV There are two common oversights by users i ensuring that the porosity values are input in percent not fractions i e for example use 25 but not 0 25 and ii
27. investigation 1 Control elevation of pond 100 ft 2 Bottom of aquifer elevation B 93 ft 3 Seasonal high water table elevation H 103 ft 4 Rise or fluctuation of water table during wet season F 4 ft 5 Hydraulic conductivity of aquifer k 10 ft day 6 Specific yield of aquifer S 25 7 Duration of wet season T 120 days 8 Length of pond L 500 ft 9 Width of pond W 200 ft Note that the wet season in the Orlando Florida area generally starts in June and extends to the end of September a period of approximately 120 days Soil borings drilled within the limits of the ponds and laboratory hydraulic conductivity tests provide estimates of the aquifer parameters The results of the model run are presented in Exhibit 4 and show a peak ground water flow rate of 13 6 gallons per minute As the output also indicates the drawdown of the water table with distance from the edge of the pond is tabulated as follows Distance From Drawdown or Long Edge of Pond Depression of Water Table 0 ft 3 00 ft 25 ft 2 46 ft 75 ft 1 69 ft 125 ft 1 16 ft 175 ft 0 80 ft 250 ft 0 43 ft 350 ft 0 20 ft 450 ft 0 09 ft August 7 1995 PONDS USER MANUAL 6 4 EXHIBIT 4 PRINTOUT OF EXAMPLE PROBLEM 4 August 7 1995 PONDS USER MANUAL 6 5 6 4 EXAMPLE 5 BASEFLOW INTO POND FOR RAPID RISE IN WATER TABLE contained in data file EXAMPLE5 DAT Consider now the same pond described in example 4 but it is re
28. perimeter of the pond which may or may not be equal to the actual perimeter of the pond The user should review the shape of the pond and draw an imaginary line around the pond through which ground water will flow unencumbered away from the pond The length of this line is the effective perimeter P See figure below for an example Since h V and P are known equations 1 and 2 above may be solved simultaneously for L and W as follows L 2 4 h 2 and P P A4xpy y 2 4 h 2 Units in the above equation must of course be consistent August 7 1995 PONDS USER MANUAL 4 5 4 4 EXAMPLE 1 EXFILTRATION TRENCH contained in data file EXAMPLE1 DAT The objective of this example is to analyze the recovery of the treatment volume stored in an exfiltration trench Based on review of the engineering plans and site specific geotechnical data the following input parameters are selected Pond Parameters 1 Equivalent Pond Trench Length 150 00 ft 2 Equivalent Pond Trench Width 26 00 ft 3 Pond Trench Bottom Elevation 91 50 ft 4 Porosity of Material Within Pond Trench 44 5 Aquifer Parameters 5 Base of Aquifer Elevation 90 00 ft 6 Seasonal High Water Table Elevation 91 00 ft 7 Saturated Hydraulic Conductivity horizontal 34 0 ft day 8 Fillable Porosity 30 0 9 Unsaturated Vertical Infiltration Rate 17 0 ft day Runoff Treatment Volume 10 Runoff Volume 3176 0 ft 11 Percent of Run
29. the last stress period minus the direct rate of recharge on the pond cells represents the ground water baseflow into the system Hydrostratigraphic Idealization The results of the field and laboratory investigation documented in the site specific geotechnical report are used to input the following idealized aquifer parameters Surficial unconfined aquifer Layer 1 e Elevation of bottom of aquifer e Hydraulic conductivity of aquifer Note that in the pond cells the hydraulic conductivity is set to a high value of 1000 feet day to represent open water e Specific yield of aquifer e Initial ground water table elevation seasonal high water table minus rise of water table following a specified rainfall event such as a normal wet season 25 yr 24hr storm etc Example problems are described in the body of the USER MANUAL August 7 1995 APPENDIX B THEORY FOR ANALYSIS OF POND RECOVERY USING SIDE BANK OR POND BOTTOM FILTERS August 7 1995 insert paper from Scott Hayes August 7 1995 APPENDIX C THEORY FOR RECOVERY ANALYSIS OF DRY OR WET BOTTOM RETENTION PONDS USING SIMPLIFIED ANALYTICAL MODEL August 7 1995 PONDS USER MANUAL C 1 August 7 1995 PONDS USER MANUAL C2 THEORY The Simplified Analytical Method was developed to compute the time for recovery of retention ponds or exfiltration trenches in water table aquifers The assumptions of the theory are listed below The receiving aquifer system is idealized
30. the pond is at the pond bottom elevation at time t 0 Methodology August 7 1995 PONDS USER MANUAL D 7 The ground water flow model used in this evaluation is a modified version of the USGS MODFLOW model A new module has been written by the author and incorporated directly into the original MODFLOW code to simulate discharge through unsubmerged weirs orifices and notches Finite Difference Grid Since the conceptual model is symmetrical with respect to the major axes of the equivalent rectangular pond it is only necessary to model a symmetrical quarter of the pond Table D 1 on page D 13 lists the grid dimensions and spacing of the axi symmetric quarter rectangle As noted the grid comprises 60 rows by 60 columns with a nodal spacing that increases with distance from the edge of the pond Distant specified head boundaries are arbitrarily located about 1000 feet from the pond to ensure that the hydraulic stresses in the pond will not reach the boundaries during the simulation This is realistic for most practical cases Since the problem is axisymmetric no flow boundary cells are set along the axes The grid is designed so that nodes are closely spaced where steep hydraulic gradients are expected i e immediately adjacent to the pond Nodal spacings are increased by no more than 1 5 times the previous nodal spacing Note that this nodal spacing convention does not apply within the pond itself since the water surface is flat
31. water baseflow during recovery period 1440 T V gb x x cubic feet 7 74808 FS xn Note gb is input in gpm and must therefore be converted to ft3 day 2 Compute equivalent uniform recharge rate q units will be ft day PAV V FS tida ATOP 3 Compute the vertical distance between center of underdrain pipe and base of aquifer parameter a in feet t D a B H i 12 24 9 Note that the diameter of the drain pipe is input in inches and is converted to feet in the above equation as is the thickness of the gravel envelope August 7 1995 PONDS USER MANUAL E 9 4 Compute the vertical height of the water table mound above the center of the underdrain pipe parameter m in feet m H R ff Note that the diameter of the drain pipe is input in inches and is converted to feet in the above equation as is the thickness of the gravel envelope 5 Compute underdrain spacing S using the ellipse equation units will be in feet Wie 4 K 2am ft q 6 Compute total length of laterals L required L ft S 7 Compute cumulative flow rate from the theoretical length of laterals i e the flow rate through the pond outfall pipe from underdrain system _ PAV V _ 9 T 86400 fs 8 Compute flow rate per lineal foot of lateral q cfs per lineal foot August 7 1995 PONDS USER MANUAL E 10 10 11 12 Compute cumulative flow rate
32. which are connected to other waters by an artificial or intermittent water course or isolated wetlands may be used as stormwater treatment wetlands Like wet detention ponds these systems are designed to slowly release collected stormwater runoff through an outlet structure However the diversion of stormwater into the wetland for treatment should not adversely affect the hydroperiod of the wetland In addition inlet structures must be designed to preclude channelized flow and residence time within the wetland should be maximized 2 2 8 Dry Detention Ponds Dry detention ponds are normally dry storage areas which are designed to store a defined quantity of runoff and slowly release the collected runoff through an outlet structure to adjacent surface waters After drawdown of the stored runoff is complete the storage basin does not hold any water and thus the system is normally dry Dry detention basins are similar to retention systems in that the basins are normally dry The main difference between the two systems is that retention systems are designed to percolate the stored runoff into the ground while dry detention systems are designed to discharge the runoff through an outlet structure Dry detention systems have limited pollutant removal efficiency Their use is therefore limited to small drainage basins 5 acres where high ground water or slowly permeable soils preclude retention systems August 7 1995 OVERVIEW OF PONDS COMPUTER PROGR
33. 2 3 22 6 SWAIGS go eee ED Ex E I ea RUE RE meta UU RU 2 3 2 2 7 Wetlands Stormwater Management System 2 4 2 2 8 Dry Detention 2 4 3 OVERVIEW OF PONDS COMPUTER PROGRAM 3 1 3 1 GENERAL RR S RU SIRE INS S ESSE GU ERR DNUS NUS SUN e n 3 1 3 2 DESCRIPTION OF MODULES e e 3 1 3 2 1 Module 1 Retention Pond Recovery Analysis Simplified Method 3 1 3 2 2 Module 2 Retention Pond Recovery Analysis Refined Method 3 2 3 2 3 Module 3 SCS Unit Hydrograph Generation Routine 3 3 3 2 4 Module 4 Ground Water Baseflow or Background Seepage Calculations 3 4 3 2 5 Module 5 Calculation of the Length of Side Bank 8 Bottom Filter 3 4 3 2 6 Module 6 Vertical Volume Recovery Filtration Structures aka VVRSs 3 4 3 2 7 Module 7 Underdrain Design Calculations 3 5 3 3 SALIENT FEATURES OF PROGRAM eeeeeeeeeeeeeeeeeeeeeeeee 3 5 3 3 1 Interactive HELP y ene eee woah ete Gig dow scape ERE here scans 3 5 3 3 2 Report Quality 3 5 3 3 3 Standardized Function 3 6 3 3 4 Request For Geotechnical Services 3 7 August 7 1995 Page No RETENTION POND RECOVER
34. 2 ft 2 Bottom of aquifer elevation B 96 ft 3 Seasonal high water table elevation H 104 ft 4 Rise or fluctuation of water table during wet season F 4 ft 5 Hydraulic conductivity of aquifer k 7 ft day 6 Specific yield of aquifer S 25 7 Duration of wet season T 120 days 8 Length of underdrain L 600 ft 9 Width of underdrain W 2 5 ft The results of the background seepage run for this problem are included in Exhibit 6 As noted the estimated seepage from the road underdrains is 6 67 gpm Therefore the total baseflow into the pond is sum of the contribution from background seepage and flow from the road underdrain system or 20 22 gpm The model predicts a water table drawdown profile as follows Distance From Draw Down Or Long Edge of Underdrain Depression of Water Table 0 ft 2 00 ft 0 3 ft 1 99 ft 1 3 ft 1 97 ft 3 1 ft 1 93 ft 6 9 ft 1 85 ft 14 4 ft 1 70 ft 29 4 ft 1 44 ft 58 1 ft 1 04 ft 108 ft 0 59 ft August 7 1995 PONDS USER MANUAL 6 8 EXHIBIT 6 PRINTOUT OF EXAMPLE PROBLEM 6 August 7 1995 MODULE 5 CALCULATION OF THE LENGTH OF SIDE BANK amp BOTTOM FILTER INPUT PARAMETERS amp EXAMPLE PROBLEM August 7 1995 PONDS USER MANUAL 7 1 7 SIDE BANK AND POND BOTTOM FILTRATION SYSTEMS 7 1 GENERAL Conceptual model 2 ar ex Re RC aema see Figure 7 1 below Description of input parameters see page 7 2 Theory eos ot
35. 24 hr design storm event is created in the SWFWMD hydrograph generation module i e Example 3 1a Example 3 1b involves routing this hydrograph through a dry bottom pond which has a 7 ft wide overflow weir together with a 3 inch diameter bleed down pipe i e a sharp edged orifice It is assumed in this example that there are no ditches close enough to the pond to affect its recovery The objectives of this example are to compute the peak discharge rate and peak stage during the storm event taking into account ground infiltration during the storm August 7 1995 PONDS USER MANUAL 5 15 Table 5 5 Example Problems for Retention Pond Recovery Refined Method EXAMPLE 3 1a 3 7 3 8 3 9 APPLICATION Generate runoff hydrograph for 25 yr 24 hr storm event Route the hydrograph generated in 3 1a through a dry bottom retention pond which has multiple discharge structures an overflow weir amp a bleeddown pipe taking infiltration credit into account during the routing Same as Example 3 1b without infiltration credit Same as Example 3 1b without discharge structures i e a closed pond Note that closed ponds are usually designed for a 100 yr 24 hr storm event but the 25 yr 24 hr hydrograph is used here only for illustrative purposes Same as Example 3 1b without discharge structures and infiltration credit This is a worst case situation Recovery of water quality volume for dry bottom pond in Example
36. 7 1995 PONDS USER MANUAL 7 4 EXHIBIT 7 PRINTOUT OF EXAMPLE PROBLEM 7 August 7 1995 MODULE 6 CALCULATION OF OF VERTICAL VOLUME RECOVERY FILTRATION STRUCTURES aka VVRSs INPUT PARAMETERS amp EXAMPLE PROBLEM August 7 1995 PONDS USER MANUAL 8 1 8 VERTICAL VOLUME RECOVERY STRUCTURES 8 1 GENERAL Conceptual model 2 e ex Re RC C C see Figure 8 1 below Description of input parameters see page 8 2 eos ot el axe ERR IURIS ka e ela n see Appendix F Example Problems ka kaes ae vk na atakk pp 8 3 Figure 8 1 Conceptual Model of Vertical Hollow Cylindrical Filter August 7 1995 PONDS USER MANUAL 8 2 LIST OF INPUT PARAMETERS PARAMETER DESCRIPTION Pond amp Stormwater Volume Parameters Treatment volume V cubic feet Top elevation of treatment volume TOP ft datum Bottom elevation of treatment volume BOT ft datum Tailwater or invert elevation TWL ft datum VVRS Details Inside diameter of VVRS structure Din ft Outside diameter of VVRS structure Dout ft Elevation of top of concrete base BASE ft datum Hydraulic conductivity of filter media k ft day Design Criteria Recovery Time T day Factor of Safety FS dimensionless Background Seepage Ground water baseflow into pond qb gpm 8 2 SYMBOL TOP BOT TWL Din Dout BASE qb August 7 1995 PONDS USER MANUAL 8 3 8 3 EXAMPLE 8 RECOVERY
37. 9 5 12 EXPLANATION OF CERTAIN ASPECTS OF THE PROGRAM 5 11 5 13 EXAMPLE PROBLEMS owes eese eoe e ERR ees x ER RN QE RUE M TT 5 12 5 13 1 Description of Example Problems 5 12 5 13 1 1 General oue ere e AVE ER CERNI M E Rr 5 12 5 13 1 2 Examples 3 1 amp 3 1b 5 12 5 13 1 3 Example 3 2 ceo lE kaa a E EE 5 14 5 13 1 4 Example 3 3 iu pit aaa eii e eae danse LI wees 5 14 5 13 1 5 Example 3 4 52 dose i Re iue eames 5 14 5 13 1 6 Examples 83 5 amp 3 6_ 5 14 5 13 1 7 Examples 23 7 amp 3 8_ 5 14 5 13 1 8 Example 3 9 miin sa ete eed eid edie E Yeh 5 15 5 13 2 Input Parameters siiis 555 06 cb Ly RES E er ASI Reed US wee ts 5 17 5 13 2 1 Examples 3 1 through 3 8_ 5 17 5 13 2 3 Example 3 93 ker gx dyed ue Sew 5 17 5 13 3 Results kka E e RE dr 5 22 GROUND WATER BASEFLOW MODULE eeeeeeeeeeeeeeeeeeeeee 6 1 6 1 GENERAL eor UP OE EIS SI e ere ALIIS IRURE TS mice tls 6 1 6 2 LIST OF INPUT PARAMETERS 6 2 6 3 EXAMPLE 4 BASEFLOW INTO POND FOR GRADUAL RISE IN WATER TABLE 6 3 6 4 EXAMPLE 5 BASEFLOW INTO POND FOR RAPID RISE IN WATER TABLE 6 5 6 5 EXAMPLE 46 BASEFLOW INTO POND F
38. A by product of the analysis is the ground water baseflow into the ditch which is an important result for selecting pump sizes etc Southwest Florida Water Management District SWFWMD has in a previous technical procedure defined the drawdown impact distance as the distance to the 0 10 foot drawdown contour assuming the following i no rainfall recharge over a 30 day period and ii the wet season water table is the initial condition Onthe other hand South Florida Water Management District SFWMD specifies the impact distance as the distance to the 1 ft drawdown contour after 90 days of no rainfall recharge using the dry season water table as an initial condition These criteria are summarized in Table 5 6 below Table 5 6 Summary of Regulatory Criteria for Defining Drawdown Impact Distance Avene Duration of Rainfall Water Table Initial SENEN simulation Recharge Drawdown Water Table SWFWMD 30 days None 0 10 ft wet season SFWMD 90 days None 1 00 ft dry season As mentioned previously three typical hydro stratigraphic cases are shown in Figure 5 2 Guidelines for the selection of aquifer parameters and the control elevation for these cases are presented in Table 5 7 August 7 1995 PONDS USER MANUAL Figure 5 2 Hydrostratigraphic Variations for Ditch Dewatering Impacts August 7 1995 PONDS USER MANUAL 5 19 Table 5 7 Recommendations for Selecting Aquifer Parameters for Dewatering Analysis
39. AM August 7 1995 PONDS USER MANUAL 3 1 3 OVERVIEW OF PONDS COMPUTER PROGRAM 3 1 GENERAL PONDS is an interactive menu driven ground water surface water computer program which was written specifically for analyzing stormwater management and percolation ponds Interactive graphical and text help screens are provided in all modules Although there are numerous other engineering applications for the generic modules they have been tailored to perform design calculations for most of the typical stormwater management systems permitted in the state of Florida The methodologies in the PONDS computer program are formally approved by the St Johns River Water Management District and the program is also used by the Southwest Florida Water Management District for permit review purposes 3 2 DESCRIPTION OF MODULES The program presently has seven 7 modules or menu options Brief descriptions of the capabilities and applications of each of these modules are described in the following subsections 3 2 1 Module 1 Retention Pond Recovery Analysis Simplified Method This module calculates the time for recovery of i dry bottom or wet bottom retention ponds ii exfiltration trenches and iii swales following a slug or instantaneous filling of the pond Typical water management district permit criteria require that the water quality aka pollution abatement or treatment volume instantaneously fill the pond without credit for ground infiltrati
40. Baseflow DOS 2 0 or higher 8086 80286 80386 amp 80486 with numeric coprocessor All Other Modules DOS 2 0 or higher 8086 80286 80386 amp 80486 1 3 PROGRAM INSTALLATION PONDS is shipped in either a 514 or 3 high density disk format Follow the steps below to install the program 1 Place the program disk in drive A or B 2 Log on to the A drive or B 3 Type INSTALL enter and follow the instructions August 7 1995 PONDS USER MANUAL 1 2 The INSTALL program will automatically set up a subdirectory for you and decompress all program and support files for you 1 4 PROGRAM SECURITY The PONDS security device is called a hardware lock The hardware lock attaches directly to any parallel port on the back of your PC The device protects PONDS from unauthorized use 1 5 PROGRAM EXECUTION You are now ready to run the program To do this return to the program directory A gt C change to C drive C gt CD PONDS226 change to program directory Before executing the program you may want to set up a separate data directory This can be on any valid disk drive preferably the hard disk and can be under a directory or subdirectory For example you can setup a subdirectory under PONDS226 called DATA This is accomplished as follows C MD PONDS226 DATA this creates a subdirectory When reading and saving data files the user should specify the data subdirectory if one is used To execute the program type PO
41. FLOW model are described in a subsequent section Transient vertical unsaturated flow is modeled using an algorithm developed by the author The details of this algorithm are descirbed in the next section Surface water discharges through free or unsubmerged weirs orifices or notches can be modeled during unsaturated or saturated flow A module to simulate these discharges have been developed by the author and incorporated into MODFLOW and the unsaturated flow algorithm Dupuit Forchheimer assumptions are applicable for saturated flow i e 1 Flow is considered to be purely horizontal 2 Flow is assumed to be uniformly distributed with depth The Dupuit Forchheimer theory loses accuracy if the depth of the impermeable layer increases because of the increased importance of vertical flow Bouwer 1969 found that the Dupuit Forchheimer theory gave reasonable results if the distance of the impermeable layer below the pond bottom was not more than twice the width of the water level in the pond Therefore twice the pond width should be greater than the pond bottom elevation minus the base of aquifer elevation for the theory to be valid August 7 1995 PONDS USER MANUAL D 4 Figure D 1 Conceptual Model of Refined Method of Retention Pond Recovery UNSATURATED FLOW ALGORITHM Unsaturated flow is computed on an incremental basis for each time step If there is discharge through the weir or orifice during unsaturated flow the algori
42. From Long Edge Column Column Row From Short Edge of Pond Numbe is de i us of Pond f r WT 60 Constant Head Anderson Mary P W W Woessner Applied Groundwater Modeling Academic Press Inc Harcourt Brace Jovanovich Publishers San Diego California 1992 References Mc Donald M G and A W Harbaugh A Modular Three Dimensional Finite Difference Ground Water Flow Model Techniques of Water Resources Investigations of the U S Gelogical Survey Chapter A1 Book 6 1988 Sebaali S J and David Sua November 30 1993 Review of PONDS Software Brooksville Permitting Department Southwest Florida Water Management District Brooksville Florida August 7 1995 APPENDIX E METHODOLOGY FOR RECOVERY ANALYSIS OF UNDERDRAINED RETENTION PONDS i e retention ponds with subsurface drains in the natural soil August 7 1995 PONDS USER MANUAL E 1 DISCUSSION OF METHODOLOGY FOR RECOVERY ANALYSIS OF UNDERDRAINED RETENTION PONDS by Devo Seereeram Ph D P E INTRODUCTION Underdrained retention pondsis a relatively new stormwater management system permitted by St Johns River Water Management District effective late 1991 In the past the term underdrain has been associated with systems which are formally known as filtration systems The new underdrain system is different from typical side bank and pond bottom filters in many respects 1 THEORY Generally on line underdrain systems require retention o
43. MANUAL F 7 Figure F 4 Flow net shape factors for horizontal flow within filter media surrounding vertical pipes Cedergren 1977 August 7 1995 PONDS USER MANUAL F 8 Since the surface area of ponds increase or stay constant with increasing stage it is conservative to assume that the area A is constant and equal to V h h 2 where V treatment or water quality volume h top elevation of treatment volume h bottom elevation of treatment volume Substituting equation 3 in 2 and introducing the factor of safety variable FS yields V h h he SN pn Yd 4 Tu 4 which may be written in differential form h max V FS 1 dt dh h h y 6 n h h CD N k Pai nj Integrating equation 5 gives the following equation for the theoretical number of VVRS structures required to recover the treatment volume V in time T max V FS 1 N dh J h h y 6 h h CO TK n where August 7 1995 PONDS USER MANUAL F 9 dn Inu y In Qu In a y f l 7 y y m The maximum and minimum flow rates qmax and q respectively through VVRS is given by the following equations ny Qmax 7 k ak y 8 n Qmin gt k Anin nin y 9 Ng If ground water baseflow contributions to the pond q are positive then the theoretical number of VVRSs required to accomodate the basefl
44. NDS and press the ENTER key 1 6 COMMON PROBLEMS 1 6 1 Hardware 1 If running the ground water baseflow module or the refined retention pond recovery module ensure the computer has a math co processor 2 A 386 or 486 computer with at least 1 MB of extended memory is required to run the refined retention pond recovery module August 7 1995 PONDS USER MANUAL 1 3 3 Check available memory on computer using for example the MEM command The maximum executable program size shall be at least 570K 1 6 2 Install Problems If you are using DOS 5 0 and get the following error message PACKED CORRUPT FILE Then reinstall using the following command LOADFIX INSTALL If you do not have a math co processor the install program may return a syntax error message You need a math coprocessor to run two modules in PONDS ground water baseflow and the refined retention pond recovery analysis 1 6 3 Copy Protection Problems 1 Make sure the provided hardware lock is firmly attached to the parallel port on the back of your PC or the program will issue a Hardware Lock message at execution time The hardware lock must be attached to the parallel port for the duration of the PONDS session If the lock is disconnected during a model run the program will halt execution until the lock is reattached No message is displayed under these conditions 1 6 4 Missing Inadvertently Deleted Files Problem Please check to ensure the files li
45. PONDS USER MANUAL F 4 Figure F 2 Gradation Curve for VVRS Filter Media August 7 1995 PONDS USER MANUAL F 5 THEORY Horizontal flow through a hollow cylindrical sand filter is similar to flow through a vertical sand drain well The theory of flow through vertical sand drain wells is described by H R Cedergren in the well known text book Seepage Drainage and Flow Nets pp 362 368 2nd edition John Wiley amp Sons 1977 Applying this theory to the representation shown on Figure F 3 the instantaneous Darcian flow rate q through a VVRS at any instant of elapsed or recovery time t is as follows n q kh h 1 ng where k hydraulic conductivity of filter media nin shape factor of flow net which depends on the ratio of the inside diameter to outside diameter of the VVRS filter see Figure F 4 h head at outside edge of filter at time t y tailwater elevation elevation of concrete base gt 0 Consider a time increment at in which the head drops by h causing a volume increment AV to discharge from the pond through the VVRS filters Mathematically this is equivalent to n AV A Mh NL q at N kh h y at Q n theoretical number of identical VVRS structures required to recover treatment volume A area of water surface at time t where N August 7 1995 PONDS USER MANUAL F 6 Figure F 3 Graphic illustration of geometric parameters for typical VVRS August 7 1995 PONDS USER
46. PONDS Version 2 26 eG e USER MANUAL copyright 1995 by Deve Seeweram PLD P E Ground Water Surface Water Models For Stormwater Ponds Applications Transient Infiltration Analysis of Dry or Wet Bottom Retention Ponds Exfiltration Trenches and Swales with amp without discharge structures Recovery Analysis of Retention Ponds With Standard Side Bank or Bottom Filtration Systems Recovery Analysis of Retention Ponds With Vertical Hollow Cylindrical Sand Filters aka VVRS Recovery Analysis of Retentions Ponds With Subsurface Drainage Systems aka Underdrained Retention Ponds Ground Water Baseflow Calculations amp Drawdown Analysis For Wet Detention Ponds Calculation of Dewatering Rates from and Water Table Drawdown Profiles Due to Road Underdrains Interceptor Trenches Ditches Canals Borrow Pits and Other Dewatering Systems Hydrograph Generation SCS Unit Hydrograph June 1995 THIS WORK EMBODIES CONFIDENTIAL INFORMATION AND TRADE SECRETS PROPRIETARY TO DR DEVO SEEREERAM AND SHALL NOT BE REPRODUCED COPIED USED DISCLOSED OR TRANSFERRED WITHOUT THE EXPRESS WRITTEN APPROVAL OF DR SEEREERAM WRITTEN amp DISTRIBUTED BY DEVO SEEREERAM PH D P E PROFESSIONAL GEOTECHNICAL ENGINEER 5633 PARTRIDGE DRIVE ORLANDO FL 32810 407 290 2371 VOICE 407 298 9011 FAX JULY 1995 VERSION 2 26 August 7 1995 TABLE OF CONTENTS Page No LICENSE AGREEMENT 1 GETTING STARTED
47. ROM ROAD UNDERDRAINS 6 7 TABLE OF CONTENTS continued August 7 1995 TABLE OF CONTENTS continued Page No 7 SIDE BANK AND POND BOTTOM FILTRATION SYSTEMS 7 1 7 1 GENERAL mro E IRI MER ESI MES GO sels qe se Mss s 7 1 7 2 LIST OF INPUT PARAMETERS 7 2 7 3 EXAMPLE 7 FILTRATION SYSTEM WITH BASEFLOWS 7 3 8 VERTICAL VOLUME RECOVERY STRUCTURES 8 1 8 1 GENERAL 5 er erates x ENTIRE e 8 1 8 2 LIST OF INPUT PARAMETERS 8 2 8 3 EXAMPLE 8 RECOVERY ANALYSIS OF RETENTION POND WITH VVRS FILTERS 8 3 9 UNDERDRAIN DESIGN CALCULATIONS 0 cece cece ccc cc err rn 9 1 9 1 GENERAL eic pU eU ie OCC ie e OPI 9 1 9 2 LIST OF INPUT PARAMETERS aean a a A 9 2 9 3 EXAMPLE 9 DESIGN OF UNDERDRAIN POND 9 3 LIST OF TABLES Table 1 1 List OF Files e tm k te ea 1 4 Table 5 1 List of Input Parameters 5 2 Table 5 2 Special Function Keys for Refined Recovery Analysis Module 5 4 Table 5 3 Typical Weir Equations for Free 5 6 Table 5 4 Symbols amp Description of Flow
48. TIC D 1 ALGORITHM FOR UNSATURATED FLOW CALCULATIONS Compute inflow volume increment AV into pond during computational time step i of duration At Add this volume increment to the volume of water if any V which was in the pond at start of time step i to obtain V Compute maximum potential volume V that can be infiltrated during bottom area and da filbrabioth a adeatkllable at the start of time step 4 Vah based on the bottom area A the fillable porosity of the soil and the distance between the water table and the pond bottom August 7 1995 PONDS USER MANUAL D 6 step Z4 If V is less than V and also less than V then the volume infiltrated during the time step is equal to V and the pond is dry during this time step If V is greater than Vaalo then Veces 18 the balance which goes into EA d than steczaegexelume iba dene fey atten portion moda ee d SH ate How ORT stage height which produces a volume balance of the following equation Vol above lowest discharge discharge volume V 7 Volume below lowest discharge SATURATED FLOW ALGORITHM Saturated flow commences after unsaturated flow is complete It is possible to deactivate the unsaturated flow algorithm and assume saturated flow conditions at the initiation of the storm If such an option is selected the model assumes that the water table directly beneath
49. Y ANALYSIS SIMPLIFIED METHOD 4 1 4 1 GENERAL 74 43 err edF ERU ase al GUN S NOE eR i aoo Ge MIS T oss 4 1 4 2 LIST OFINPUT PARAMETERS ncn nn orar ncm y c n n en 4 2 4 3 CALCULATION OF EQUIVALENT POND WIDTH amp LENGTH 4 3 4 4 EXAMPLE 1 EXFILTRATION TRENCH 4 5 4 5 EXAMPLE 2 DRY BOTTOM RETENTION POND 4 7 RETENTION POND RECOVERY ANALYSIS REFINED METHOD 5 1 5 1 CONCEPTUAL MODEL Rr en Rr evans a aE oie aa ieee aa S 5 1 5 2 LIST OF INPUT PARAMETERS cece ccc cree crete eee 5 2 5 3 MODEL LIMITATIONS 5 5 exer e ewe ES ee Gig ie NES PE 5 3 5 4 SUPPLEMENTAL FUNCTION KEYS 5 4 5 5 HYDROGRAPH INPUT RR IR SE TAS ER ES S Mes 5 5 5 5 6 INTERFACING WITH ADICPR 5 6 5 7 MODELING OF DISCHARGE STRUCTURES 5 6 5 8 SWFWMD HYDROGRAPH GENERATION MODULE 5 7 5 8 1 General i veu e er Rer ER ERR SER SURGE 5 7 5 8 2 User Specified Rainfall Distribution amp Unit Hydrograph 5 7 5 9 GRAPHIC DISPLAY OF RESULTS eeeeeeeeeeeeeeeeeeeeeeee 5 8 5 10 PARTIALLY LINED PONDS sacs cies Rx aS ane 5 9 5 11 FLOW TYPESYMBOLS ices osc e t RR RR Re he me Ree sh E eee 5
50. allel to the X axis then the model assumes that there are ditches symmetrically placed with respect to that axis In other words if the user specifies a ditch 40 ft east of the pond the model assumes that there is another ditch 40 ft west of the pond i e a mirror image This limitation must be appreciated Simulation of Discharge Through Unsubmerged Weirs Notches and Orifices The MODFLOW DRAIN module is designed to simulate the effects of features such as agricultural drains which remove water from the aquifer at a rate proportional to the difference between the head in the aquifer and some fixed head or elevation so long as the head in the aquifer is above that elevation There is no discharge if the head in the aquifer falls below the control level of the drain The MODFLOW DRAIN package models discharge using the following linear relationship q Cy lt h d gt 1 where C drain conductance ft s q discharge in ft3 s h head in the aquifer ft datum d drain invert or tailwater elevation Note that the operator lt gt indicates that the value is always positive and zero if it is negative The general form of the equation for free discharge i e unsubmerged conditions through a weir or orifice is q C lt h d gt XQ cde Q lt h d gt uu 2 weir discharge coefficient weir exponent where C n August 7 1995 PONDS USER MANUAL D 10 d weir discharge elevation or centroid of ori
51. ance August 7 1995 PONDS USER MANUAL D 13 This modified drain conductance equation has been verified by testing it against closed form solutions and by independent evaluators see for example Seebali and Sua 1993 A verification problem is present below For a circular sharp edged orifice the drawdown equation is as follows jos nee 2xLxw where C 0 6 x 2g weir discharge coefficient g 32 16 ft sec A area of orifice in ft t drawdown time in seconds L pond length in ft W pond width in ft h initial head in ft h final head in ft Example problem C 4 812 ft sec A 05811 t t 216000 sec i e 60 hr L 431 ft W 220 ft h 13 ft h 2 ft N From the equation above h 0 675 ft If a low permeability is set for the aquifer say 0 05 ft day PONDS reproduces this closed form solution August 7 1995 PONDS USER MANUAL D 14 Table D 1 Grid Dimensions For Axisymmetric Representation of Rectangular Pond L Length W Width Offset Distance From Long Edge of Pond f IIT f Number f moms o 9 variable head 2 10 variable head 2 11 variable head 2 12 variable head gt 4 2 s 13 variable head gt 4 2 A 14 variable head 2 15 variable head gt 4 2 16 variable head 2 17 variable head gt a 2 18 variable head 2 19 variable head 2 20 variable head Sa 2 21 variable head 4 3 22 variable head 3 23 variable h
52. and outside diameters about 6 feet The annular space is backfilled with fine aggregate filter media forming a hollow cylindrical filter As shown on Figure F 2 the gradation of the typical VVRS filter sand is just within the coarse side of the allowable gradation limits It is specially blended by commercial aggregate suppliers such as Florida Rock The effective grain size D is 0 50 mm and the uniformity coefficient D D is 4 0 Hydraulic conductivity values of this filter media is typically on the order of 200 feet day VVRSs are located within the pond not in the side slopes and the base of the structure is usually established 2 to 4 feet below the pond bottom or normal water level A wedge of to 1 inch gravel backfill is placed around the portion of the structure beneath the pond bottom Advantages of VVRS over Conventional Filters VVRSs are above ground and therefore visible to maintenance personnel who can observe their performance first hand The structure is designed such that the filter media and filter fabric can be periodically replaced without total replacement of the system If minor clogging of the filter media occurs the system can be backflushed VVRSs are easy to install and can be cost effective in the long term August 7 1995 PONDS USER MANUAL F 3 Figure F 1 Typical Detail for note geonets are recommended on inside face of outside cylinder and outside face of inside cylinder August 7 1995
53. can be run using the recommendations in Table 5 7 When printing the output for these examples please remember to specify in the printing options that the ground water mound should be printed at each time step August 7 1995 PONDS USER MANUAL 5 20 Table 5 8 Input Data amp Results Postdevelopment Runoff Parameters PARAMETER DESCRIPTION MAGNITUDE Area of contributing drainage basin acre 10 Directly Connected Impervious Area 30 Curve Number for Pervious Area 70 Time of concentration minutes 20 Storm Duration hour 24 Rainfall Depth for 24 hr 25 yr return period inch 8 6 Unit Hydrograph Shape Factor 484 Rainfall Distribution Calculated peak discharge rate SCS Type II FI Modified 37 67 Time to peak discharge rate 12 04 Calculated total runoff volume 217 290 Table 5 9 Input Data amp Computation Water Quality Volume PARAMETER DESCRIPTION UNIT MAGNITUDE Area of Contributing Drainage Basin acre 10 Directly Connected Impervious Area DCIA 9 30 00 Area other than DCIA pervious area acre 7 0 Directly Connected Impervious Area acre 3 0 Curve Number for Pervious Area 70 Rainfall Depth inch 1 Runoff Depth from Pervious Area inch 0 005 Runoff Depth from DCIA inch 0 821 Pond Area ft 42 336 Treatment Volume for Dry Retention Pond t 12 581 Treatment Volume for Wet Detention Pond ft
54. ce 43 ft SFWMD Impact distance 117 ft SWFWMD August 7 1995 MODULE 4 GROUND WATER BASEFLOW OR BACKGROUND SEEPAGE INPUT PARAMETERS amp EXAMPLE PROBLEM August 7 1995 PONDS USER MANUAL 6 1 6 GROUND WATER BASEFLOW MODULE 6 1 GENERAL Conceptual model 2 ar ex Re RC CR OR see Figure 6 1 below Description of input parameters see page 6 2 saamid meal ON d ADR ala see Appendix A Example Problems ee de SA eae eae pp 6 3 through 6 8 Figure 6 1 Conceptual Model For Ground Water Baseflow Module August 7 1995 PONDS USER MANUAL 6 2 6 2 LIST OF INPUT PARAMETERS 1 Equivalent Pond Length L 2 Equivalent Pond Width W 3 Control elevation of pond O 4 Bottom of aquifer elevation B 5 Hydraulic conductivity of aquifer k 6 Specific yield of aquifer S Ts Seasonal high water table elevation H 8 Rise or fluctuation of water table during wet season F or any other arbitrary duration time period specified by the user 9 Duration for rise of water table T August 7 1995 PONDS USER MANUAL 6 3 6 3 EXAMPLE 4 BASEFLOW INTO POND FOR GRADUAL RISE IN WATER TABLE contained in data file EXAMPLE4 DAT The objective of this example is to estimate the peak ground water seepage into a pond for a normal wet season in the Orlando area given the following pond dimensions and aguifer parameters estimated from a site specific
55. defects in material and workmanship under normal use for a period of ninety 90 days from the date of delivery to you by Devo Seereeram LIMITATIONS OF REMEDIES Devo Seereeram s entire liability and your exclusive remedy shall be the replacements of any diskette s not meeting Devo Seereeram s Limited Warranty and which is returned to Devo Seereeram with a copy of your receipt or other evidence of payment or August 7 1995 PONDS LICENSE AGREEMENT Page 3 of 3 if Devo Seereeram is unable to deliver replacement diskette s which is free of defects in materials or workmanship you may terminate this Agreement by returning the Program and any money paid by you to Devo Seereeram will be refunded In no event will Devo Seereeram be liable to you for any damages including any lost profits lost savings or other incidental or consequential damages arising out of the use or inability to use such program even if Devo Seereeram has been advised of the possibility of such damages or for any claim by any other party Some states do not allow the limitation or exclusion of liability for incidental or consequential damages so the above limitations or exclusions may not apply to you GENERAL You may not sublicense assign or transfer the license or the Program except as expressly provided in this Agreement Any attempt otherwise to cubicles assign or transfer any rights duties or obligations hereunder is void This Agreemen
56. ds Ditches Trenches Roadway Underdrains Borrow Pits Etc by Devo Seereeram Ph D P E ABSTRACT This is an explanation of a simple rational procedure for estimating drawdown impact distances and background ground water inflow into ponds or other systems where the control water level is established below the normal seasonal high water table The need for a consistent easily understood calculation of this type is becoming much more important as the study of wetland dehydration and other ground water resource impacts are areas of increasing concern INTRODUCTION Except for experienced ground water modelers the USGS MODFLOW computer code is not widely used by the engineering practitioners due to the time consuming nature and complexity in setting up the input files for these models and interpreting their output However PONDS has been developed as a convenient pre processor and post processor for the USGS MODFLOW model which allows menu driven setting up of a problem using easily understood inputs and viewing meaningful results in a matter of minutes The following describes how PONDS is used for calculating simultaneously the drawdown versus distance curve and the background ground water flow rate into a pond or other dewatering system such a drainage ditch canal underdrain interceptor trench borrow pit etc GENERAL EXPLANATION OF PHENOMENA Drawdown is a transient phenomena which takes place as the ground water level rises in
57. e main menu has additional file management modules including modules to save data files and read previously saved data files 3 3 SALIENT FEATURES OF PROGRAM 3 3 1 Interactive HELP The input screens are interactive amp user friendly with an online HELP routine to provide a graphic explanation of each input parameter for each input screen Model inputs may be varied interactively to perform on screen sensitivity analyses prior to finalizing and printing results 3 3 2 Report Quality Output Results can be printed out in presentation quality format Results of time dependent simulations can be displayed graphically and report quality graphs can be plotted to a number of standard printers and plotters August 7 1995 PONDS USER MANUAL 3 6 3 3 3 Standardized Function Keys Function keys have been standardized for the most part in all modules Fi Help graphical screen or text file appears F2 Start Calculations after input data sheet is complete FA Print Results after calculations are complete lt 5 gt Clear the current input cell F8 Clear the current input page lt F10 gt Access ground water baseflow module from another module August 7 1995 PONDS USER MANUAL 3 7 3 3 4 Request For Geotechnical Services The input aquifer parameters are simple amp straightforward and are usually contained in site specific geotechnical reports If there is any uncertaintity the user can incorporate the text bel
58. ead 3 24 variable head 008 3 4 25 variable head 4 4 26 variable head 35 4 27 variable head 5 28 variable head 5 29 variable head 5 80 30 variable head 8 8 Column Numbe Column Spacing Offset Distance From Short Edge of Pond Row Spacing August 7 1995 PONDS USER MANUAL D 15 Offset Distance Offset Distance From Long Edge Column Column Row From Short Edge of Pond Numbe Spacing Spacing of Pond r f Number f CONTINUED ON NEXT PAGE 31 variable head 8 30 8 80 32 variable head 29 8 33 variable head o8 9 8 34 variable head qnom 10 107 35 variable head 10 10 36 variable head 0 25 10 127 37 variable head 0 24 10 38 variable head 15 39 variable head 15 40 variable head 15 41 variable head 25 42 variable head 2 9 25 43 variable head 25 8 25 44 variable head 25 297 45 variable head 40 16 40 337 46 variable head 4 B 40 377 47 variable head EMA KM 40 48 variable head 4 1 40 457 49 variable head 4 7 40 497 50 variable head oH 40 542 51 variable head 50 10 50 592 52 variable head 5 9 50 642 53 variable head 55 8 50 692 54 variable head 50 742 55 variable head 55 6 50 56 variable head 50 57 variable head 60 60 907 58 variable head 60 967 59 variable head 2 60 August 7 1995 PONDS USER MANUAL D 16 Offset Distance Offset Distance
59. ecovery period V treatment volume y tailwater elevation elevation of concrete base gt 0 Oo ll 5 un iow 3 3 5 amp c ll 5 Ze 3 2 I Z I August 7 1995
60. ed 2 to 4 feet below the pond bottom or normal water level Typical details of a VVRS are included in Appendix E VVRSs are advantageous from a maintenance standpoint since their performance can be observed first hand following storm events and they can be backflushed if clogged In August 7 1995 PONDS USER MANUAL 2 3 addition unlike the typical side bank or bottom filters the filter media can be periodically replaced without the need to completely replace the system 2 2 4 Underdrain Systems These systems consist of a dry detention basin underlain with a network of subsurface drains to i control the water table below the basin bottom and ii enhance percolation of impounded stormwater from within the pond Unlike filtration systems the backfill around the drainage pipes consists of indigenous soils typically poorly graded fine sand which provide better pollutant removal capabilities than filter media i e washed medium to coarse grained sand SJRWMD requires at least 2 feet of soil cover between the bottom of the basin and the underdrain pipes 2 2 5 Exfiltration Trench An exfiltration trench is a subsurface system consisting of a large diameter perforated pipe or Infiltrator chambers surrounded by coarse aggregate which temporarily stores and infiltrates stormwater runoff Stormwater enters the conduit and infiltrates through the base and sides of the trench into the shallow ground water aquifer The perforated pipes or
61. ed in the PONDS226 GRAPHICS LCOM CHR subdirectory LITT CHR SANS CHR SCRI CHR SIMP CHR TRIP CHR TSCR CHR CONTINUED ON NEXT PAGE August 7 1995 PONDS USER MANUAL 1 8 Table 1 1 List of Files File Name Description PLOT CFG PONDS configuration files PRINTER CFG These files are located in the PONDS226 GRAPHICS SCREEN CFG subdirectory _UJ INI Font information files for LaserJet amp Postscript printers _LJ3R INI These files are located in the PONDS226 GRAPHICS _L4 1NI subdirectory PS INI _PS PRO Postscript header file These files are located in the PONDS226 GRAPHICS subdirectory SCREEN INI Plot initilization files used by PONDS to control plot LASER INI attributes such as colors line styles line thicknesses etc DJ INI These files are located in the PONDS226 GRAPHICS DM INI subdirectory PLOTTER INI August 7 1995 OVERVIEW OF STORMWATER MANAGEMENT SYSTEMS August 7 1995 PONDS USER MANUAL 2 1 2 OVERVIEW OF STORMWATER MANAGEMENT SYSTEMS 2 1 GENERAL Historically stormwater management systems have been regulated by both the Florida Department of Environmental Protection FDEP and the water management districts WMDs with FDEP rules governing water quality treatment and WMD Management and Storage of Surface Water MSSW rules governing water quantity considerations such as drainage and flood control In 1989 the Florida legislature gave the water management distr
62. edimentation i e wet detention The filter trench is normally backfilled to the surface with fine aggregate such as washed sand that is more permeable than the surrounding soil SJRWMD requires that the water quality volume flow through at least 2 feet of fine aggregate filter media before discharge into the filter drain pipe Filters are normally installed in the bottom or banks of detention basins and may be used in either dry or wet basins Filters are a maintenance intensive BMP because of the likelihood of clogging over time and their use is usually restricted to projects with a contributing drainage area of less than 10 acres Until recently filters were commonly known as underdrains but with the introduction of the Underdrain system in SJRWMD which differs from filters it is important to be aware of the correct terminology 2 2 9 8 Vertical Hollow Cylindrical Sand Filter aka This is an alternative filtration system to the more common side bank and pond bottom filters described above The VVRS consists of two concentrically and vertically placed perforated aluminum pipes which are set on a concrete base The diameters of the inside and outside pipes are selected to provide a minimum annular space of 2 feet The annular space is backfilled with fine aggregate filter media as per SJRWMD criteria forming a hollow cylindrical filter VVRSs are located within the pond not in the side slopes and the base is usually establish
63. ent water table The results can be displayed and or printed in report quality graphical format a An option is included to use the refined model for water quality or pollution abatement volume recovery i e slug loading of a known volume of water Ponds which are partially lined can also be modeled Ground water mounding due to hydraulic loading in wastewater percolation ponds and septic drainfields can be modeled 3 2 3 Module 3 SCS Unit Hydrograph Generation Routine The calculation routines for this SCS unit hydrograph generation module were written by Sam Seebali P E and David Sua P E of the Southwest Florida Water Management District Brooksville Florida This module generates hydrographs for a single drainage basin it does not allow the user to create composite hydrographs for multiple basins The hydrograph data generated in this module can be imported for use in Module 2 August 7 1995 PONDS USER MANUAL 3 4 3 2 4 Module 4 Ground Water Baseflow or Background Seepage Calculations This module calculates the peak ground water baseflow into retention and wet detention ponds in water table unconfined aquifers which have their control elevations set below the seasonal high water table A by product of this numerical analysis is the induced draw down of the water table as a function of distance from the edge of pond This module has amultitude of other applications including the ability to simulate borro
64. ently wet ponds which are designed to slowly release collected stormwater runoff through an outlet structure Wet detention systems are the recommended BMP for sites with moderate to high water table conditions Wet detention ponds may have a vegetated littoral zone which treat stormwater by physical chemical and biological processes These ponds are sized to contain a permanent pool of water which August 7 1995 PONDS USER MANUAL 2 2 results in an average residence time of at least 14 days during the wet season Ground water inflow baseflow must be considered when the control elevation is set below the normal ground water table elevation or the project utilizes road underdrains to control ground water conditions on the site The design of the outfall structure must provide for the discharge of ground water baseflow at the design normal water level in the pond Baseflow rates must also be included in the drawdown calculations for the outfall structure and must be considered in the permanent pool residence time design 2 2 3 Filtration Systems 223 1 Side bank and Pond bottom Filters Filtration systems consist of a perforated pipe which collects and conveys stormwater following infiltration through a sand filter Filters are generally used where space hydraulic conductivity of the uppermost aquifer and or high water table conditions preclude recovery of the stormwater treatment volume by natural percolation i e retention systems or s
65. ereeram provides this program and documentation collectively referred to as the Program and licenses its use in the United States and Puerto Rico You assume responsibility for the selection of the Program to achieve your intended results and for the installation use and results obtained from the Program LICENSE You may D use the Program on a single machine copy the Program into any machine readable or printed form for backup purposes in support of your use of the Program on the single machine transfer the Program and license to another party if the other party agrees to accept the terms and conditions of this Agreement If you transfer the Program you must at the same time either transfer all copies whether in printed or machine readbale form to the same party or destroy any copies not transferred this includes all modifications and portions of the Program contained or merged into other programs In addition you must at the time of the transfer notify Devo Seereeram in writing of said transfer You must reproduce and include the copyright notice on any copy modification or portion of the Program merged into other programs You may not use copy modify or transfer the program or any copy modification or merged portion in whole or in part except as expressly provided for in this license August 7 1995 PONDS LICENSE AGREEMENT Page 2 of 3 If you transfer possession of any copy modification or merged portio
66. ery of the water quality volume for the dry bottom pond described in Example 3 1 Unsaturated infiltration is not considered in Example 3 5 while it is in Example 43 6 5 13 1 7 Examples 43 7 amp 438 Example 3 7 assumes that the pond bottom is wet i e the ambient water table elevation is assumed to be the same as the bleed down orifice and treatment of the water quality volume is by wet detention processes A 3 inch diameter bleed down pipe is used to recover the water quality volume Infiltration positive or negative credits are allowed during the simulation Example 3 8 is the same as Example 3 7 but does not allow credit for simultaneous infiltration during recovery of the water quality volume through the orifice August 7 1995 PONDS USER MANUAL 5 17 D 13 1 0 Example 43 9 In addition to the Background Seepage module in PONDS the Retention Pond Recovery Refined Method module can also be used to simulate dewatering due to ditching borrow pits stormwater ponds controlled below the seasonal high water table etc The numerical techniques used in these modules are different and it is recommended that the Background Seepage module be used for modeling situations where the drawdown impact distance is expected to exceed 800 ft Example 3 9 illustrates a dewatering application using the Refined Method for simulating the drawdown of the water table adjacent to a ditch for the typical hydrostratigraphic cases in Figure 5 2
67. f 66 of the first flush retention volume required for filtration systems Asa result underdrain systems use smaller ponds which are generally the same size as dry retention ponds In addition filtration systems are generally not permitted for systems which have a contributing drainage area greater than 10 acres in size Filtration systems are sometimes discouraged where there is discharge to sensitive water bodies The underdrain consists of perforated tubing with a filter fabric sock The tubing is buried at least 2 feet below the pond bottom in the natural soil This subsurface drainage system is laid out like an agricultural ground water control system to suppress the water table beneath the pond and provide dissipation capacity for recovery of the treatment volume in a specified period These subsurface drains are typically laid out in patterns of laterals connecting to a main line Figure E 1 shows typical layouts of these drainage networks In addition to computing the total length of subsurface drains required the drain spacing and layout is critical The drain pipe sizes must also be checked The theory for the design of underdrain systems is based on the ellipse theory illustrated on Figure E 2 This theory is well known to agricultural drainage engineers and is described in the book Drainage of Agricultural Land A Practical Handbook For the Planning Design August 7 1995 PONDS USER MANUAL E 2 Construction and Maintenance o
68. f Agricultural Drainage Systems by the Soil Conservation Service of the USDA August 7 1995 PONDS USER MANUAL E 3 Figure E 1 Various layouts of subsurface drain pipes within pond bottom USDA 1973 August 7 1995 PONDS USER MANUAL E 4 S 4 K m 2a m q K soil hydraulic conductivity amp has same units as recharge rate q Figure E 2 Illustration of the ellipse theory for calculating drain spacing USDA 1973 August 7 1995 PONDS USER MANUAL E 5 NOTATION see Figure E 3 for description of parameters PARAMETER DESCRIPTION SYMBOL Pond amp Stormwater Volume Parameters Treatment Volume PAV cubic feet PAV Area at Top of Pond ATOP square feet ATOP Vertical Distance From Natural Ground or Finished Grade to Pond Bottom ft d Note this parameter is not used in the calculations but is used to check the validity of the ellipse equation Aquifer Parameters Hydraulic Conductivity of Soil K ft day K Depth to Base of Aquifer From Pond Bottom B ft B Drain Parameters Drain diameter D inch D Thickness of gravel envelope above pipe t inch t Note set t 0 if no gravel envelope Depth of soil cover on underdrain H ft H Note usually a minimum of 2 feet of cover is required Design Criteria Recovery Time T day T Note usually 3 days Factor of Safety FS dimensionless FS Note usually a minimum of 2 and applies to recovery time Minimum distance between water table mou
69. fice To minimize modifications to the original MODFLOW code the drain conductance C of equation 1 is made a function of the head difference between the aquifer and the discharge elevation by combining equations 1 and 2 to obtain lt h 3 Equation 3 uses two parameters to model discharge from a DRAIN cell C and n whereas the original MODFLOW code used only the conductance parameter C as in equation 1 C is referred to herein as the Modified Drain Conductance The MODFLOW model uses 49 drain cells to represent the axisymmetric quarter of an equivalent rectangular pond These 49 drain cells are used to model weir discharge as outlined below for up to 3 discharge structures CASE 1 1 DISCHARGE STRUCTURE where the modified drain conductance for weir 1 is C x L x 86400 4 x 49 Conductance August 7 1995 PONDS USER MANUAL D 11 CASE 2 2 DISCHARGE STRUCTURES where the modified conductance for weir 1 is as follows C x L x 86400 4 x 25 Conductance and for weir 2 is C x L x 86400 4 x 24 Conductance August 7 1995 PONDS USER MANUAL D 12 CASE 3 3 DISCHARGE STRUCTURES where modified drain conductance for weir 1 is as follows C x L x 86400 4 x17 Conductance modified drain conductance for weir 2 is as follows C x L x 86400 4 x 16 Conductance and modified drain conductance for weir 3 C x Ly x 86400 4 x 16 Conduct
70. for the longest lateral in the system i e the lateral length specified on the input screen 4 4 1 cfs Compute minimum pipe diameter from Manning s formula for the longest lateral in the system using the following equation 3 43 x nl xq 12 x 2 2 inches 148 x n x 2L 100 Compute cumulative flow rate for the main line which is connected to P of the total length of laterals in the system P 100 q DX qs Compute minimum pipe diameter from Manning s formula for the main line in the system using the following equation wa 4x 43 x n2x inches 148 x nx 2 100 August 7 1995 PONDS USER MANUAL E 11 STANDARD NOTES 1 Laterals should be no farther than S 2 from the top of the basin 2 A gravel envelope at least 3 inches thick is recommended around the underdrain pipes If a gravel envelope is used a filter fabric will be required around this envelope 3 The underdrain pipe should have a filter fabric sock to prevent fines from moving into and clogging the perforated pipe 4 Ensure outfall elevation for system will allow gravity flow without tailwater backpressure to the underdrains 5 Theory is applicable where ground water flow is largely in a horizontal direction i e natural gradients less than 1 6 Capped amp sealed inspection and cleanout ports which extend to the ground surface are recommended at the following locations for each drain pipe a
71. general warning about using ditches Weir orifice data F1 help screen provides typical weir amp orifice coefficients Hydrograph data 5 5 INPUT lt gt shows additional function keys F9 generates hydrograph for water quality volume lt F10 gt import hydrograph data file in AdICPR format Southwest Florida Water Management District PONDS format or generic ASCII format lt F11 gt generate hydrographs to simulate long term loading of wastewater percolation ponds or septic drainfields There are five possible ways to input a hydrograph i The hydrograph may be input manually on the third page press PageDown or F9 to access using spreadsheet like commands Type the F1 key to see function keys for manual input August 7 1995 PONDS USER MANUAL 5 6 ii iii IV v The user may generate a hydrograph using the SWFWMD PONDS hydrograph generation routine accessible from the main menu Module 3 The hydrograph may then be imported by using the F10 function key from the third input page The user may import a hydrograph created using the popular AdICPR surface water model The hydrograph may then be imported by using the F10 function key from the third input page A user created ASCII data file in SWFWMD PONDS format may be imported The hydrograph may be input from a user created ASCII data file F1 F10 keys on third screen with the following format N
72. he other UHG files so it can be accessed by PONDS 5 9 GRAPHIC DISPLAY OF RESULTS The results can be displayed graphically by using the F5 function key when the tabulated results appear on the screen Relevant function keys appear at the bottom of the screen Report quality graphs can be printed out on a number of hardcopy devices including e Epson compatible 9 pin Dot Matrix Printers amp IBM Proprinter e Epson compatible 24 pin Dot Matrix IBM Proprinter X24 o IBM Quietwriter LaserJet II LaserJet III LaserJet 4 Canon Laser DeskJet monochrome DeskJet 500 color cartridge DeskJet 550C PaintJet e Postscript Hewlett Packard Plotters From the results screen the lt F8 gt function key is used to select the hardcopy output device and the port to which it is connected In addition the graphic output can be printed August 7 1995 PONDS USER MANUAL 5 10 to a file for future printing To print a graph saved in a file do not use the DOS PRINT command use instead the DOS COPY command as follows COPY Filename PRN B In addition to the printer devices listed above an option has been provided to allow installation of printer drivers which may become available Once the graph is displayed the F5 function key allows the user to rescale the time axis for detailed viewing printing of selected portions of the simulation The lt F2 function key gives an interactive tabulated summary of the
73. he simulation of recovery of the treatment or water quality volume or other situations where regulations do not allow credit for ground infiltration or discharges to surface waters during storm events However particularly for well drained soils with deep water tables a significant portion of the runoff volume entering a pond can infiltrate into the aquifer during the storm event By taking credit for the infiltration which occurs during the storm event a design engineer can optimize the detention volume required for attenuation of peak flow rates Such an analysis necessarily combines elements of surface water and subterranean hydrology since inflows to the pond and the ground water and surface water discharges take place simultaneously In addition the methodology must allow for time dependent variable inflow rates as generated by synthetic rainfall distributions for design storm events The computer code selected for this coupled ground water surface water interaction model of stormwater ponds is the USGS MODFLOW computer program Mc Donald and Harbaugh 1988 This is a fully three dimensional finite difference numerical technique for modeling ground water flow The original MODFLOW code was modified by the author to include modules which have the ability to simulate discharges through typical pond control structures such as weirs and orifices The modified MODFLOW code represents an integrated approach which circumvents the difficulty and im
74. icts clear authority and directive to regulate all aspects of stormwater management systems including both stormwater quantity and quality under the WMD MSSW rules As a result most of the WMDs including St Johns River Water Management District now regulate all aspects of stormwater management systems under their rules with statewide oversight provided by the FDEP Currently both FDEP and the WMDs require that any new development must have a comprehensive stormwater management system which incorporates a number of different Best Management Practices or BMPs to ensure that stormwater is being effectively treated 2 2 DESCRIPTION OF SYSTEMS Some of the more common BMPs recommended by the St Johns River Water Management District SJRWMD are described in the subsequent sections 2 2 1 Retention Systems These are storage areas designed to store a defined quantity of runoff allowing the runoff to percolate through the permeable soils of the basin floor and side slopes into the shallow groundwater aquifer The most common type of retention system consists of man made or natural depressional areas where the floor is graded as flat as possible and turf is established to promote infiltration and stabilize basin slopes Soil permeability and water table conditions must be such that the retention system can percolate the desired runoff volume within a specified time following a storm event 2 2 2 Wet Detention Ponds Wet detention ponds are perman
75. ilter required to recover the pollution abatement volume and background seepage components given the following pond data Stage Storage Data Surface area of pool at top of volume to be filtered 100 000 ft Surface area of pool at lowest level where water can enter the filter 4 78 624 ft Head difference between pool stage at A and drain pipe centerline hp 4 9 ft Head difference between pool stage at A and drain pipe centerline h 0 9 ft Volume between A and A 357 248 ft 8 20 acre ft Treatment Volume Data Pollution abatement or treatment volume 340 000 ft 7 81 acre ft Therefore Percent Recovery Treatment Volume Volume between A and Apot 95 296 Drawdown time for pollution abatement volume t 3 days Filter Details Side slope of pond S 4 Horiz 1 Vert Hydraulic conductivity of filter media 60 ft day Thickness of filter media X 2 ft Maximum effective length of filter pool interface L 2 8 ft Background Seepage Total baseflow into pond from ground water see results of example 4 13 55 gpm Total baseflow into pond from roadway underdrain see results of example 6 6 67 gpm Therefore total baseflow 20 22 gpm Factor of Safety Factor of safety for analysis 2 0 The output results of the analysis are presented in Exhibit 7 and shows that the length of filter reguired is 1227 feet with a factor of safety of 2 This computed length includes allowances for the baseflows August
76. in H ft H Design Criteria Recovery Time T day T Factor of Safety FS dimensionless FS Minimum distance between water table mound and pond bottom R ft R Background Seepage Ground water baseflow into underdrained pond qb gpm qb Parameters to Compute Minimum Diameters of Lateral Drain and Main Drain Manning s n Value For Lateral Drain Pipe dimensionless n1 Slope of Lateral Drains 11 96 i1 Maximum Length of Single Lateral Drain ft Manning s n Value For Drain Pipe dimensionless n2 Slope of Main Drain I2 96 i2 Percent of Total Length of Laterals Connected To Main Drain P P August 7 1995 PONDS USER MANUAL 9 3 9 3 EXAMPLE 9 DESIGN OF UNDERDRAIN POND contained in data file EXAMPLE9 DAT Assume that the pond described in example 4 is to be designed as an underdrain system and an outfall is available to allow gravity flow of the subsurface drainage system The following are the model input parameters Pond amp Stormwater Volume Parameters Treatment Volume PAV cubic feet 340 000 ft Area at Top of Pond ATOP square feet 100 000 ft Vertical Distance From Natural Ground or Finished Grade to Pond Bottom d ft 5 ft Aquifer Parameters Hydraulic Conductivity of Soil K ft day 10 ft day Depth to Base of Aquifer From Pond Bottom B ft 7 feet Drain Parameters Drain diameter D inch 6 inches Thickness of gravel envelope above pipe t inch 3 inches Depth of soil co
77. key results When printing the graphs there is an option for using a data thinning algorithm instead of plotting all the points This is used for distinguishing the line types on the printer when there are many data points it does not change the results The graphics routine is written in Borland Turbo C and the graphic drivers are included in the subdirectory GRAPHICS under the PONDS226 directory Drivers can only be accessed if they are located in this subdirectory Drivers are provided for screen and hardcopy devices However only the VGA screen mode is supported at this time 5 10 PARTIALLY LINED PONDS Unsaturated vertical flow prior to saturated lateral flow in partially lined ponds can be modeled as follows The first stage in the stage area data must correspond to elevation of the top of the liner i e assumed pond bottom while the last stage must correspond to the top of the unlined slope The maximum area available for unsaturated flow must be set to some arbitrary positive value less than the surface area at the first stage elevation The model simulates the increase in unsaturated infiltration rate as the water spreads out above the liner elevation Saturated flow commences when the soil storage volume beneath the unlined slope is consumed during unsaturated flow 5 11 FLOW TYPE SYMBOLS August 7 1995 PONDS USER MANUAL 5 11 Table 5 4 lists the flow types that can occur during a simulation The
78. lic conductivity Fillable porosity of aquifer Base elevation of aquifer Initial water table elevation usually the seasonal high water table ED Ww If the ground water mound is expected to intersect the pond bottom the hydraulic conductivity of the cells within the pond is automatically set to a high value 1000 ft day However if the user indicates that the ground water mound will not intersect the pond bottom the program appropriately sets the hydraulic conductivity within the pond cells to the same value as the aquifer Time Discretization amp Recharge Each time increment of the input hydrograph where saturated flow occurs is equivalent to a MODFLOW stress period Therefore if the hydrograph has 600 data points there will be 599 MODFLOW stress periods Volumetric inflow to the pond is simulated using the MODFLOW recharge package The volume entering the pond during a time increment of the input hydrograph is converted to an equivalent uniform recharge rate over the pond cells Similarly time varying recharge to the water table in ft day outside the pond may also be specified on each line of the hydrograph input August 7 1995 PONDS USER MANUAL D 9 Influence of Adjacent Ditches Adjacent ditches or canals are simulated using specified head cells in the corresponding row or column which is specified by the user by an offset distance from the edge of the pond Since the model is axi symmetric if a ditch is specified par
79. n Exhibit 8 the number of vertical hollow cylindrical sand filters VVRS recommended is 19 for this particular pond For comparison the same pond required 1227 lineal feet of side bank filter Example 7 or 5118 lineal feet of lateral underdrain Example 9 August 7 1995 PONDS USER MANUAL 8 4 EXHIBIT 8 PRINTOUT OF EXAMPLE PROBLEM 8 August 7 1995 MODULE 7 UNDERDRAIN DESIGN CALCULATIONS INPUT PARAMETERS amp EXAMPLE PROBLEM August 7 1995 PONDS USER MANUAL 9 1 9 UNDERDRAIN DESIGN CALCULATIONS 9 1 GENERAL Conceptual model 2 er ex Re RC ke 8 OR see Figure 9 1 below Description of input parameters see page 9 2 axe IER S RURSUS ERR UON d ADR saa see Appendix E Example Problems ione ae Co nne dice Ned epe qm ROUTINE a i eae ar pp 9 3 Figure 9 1 Conceptual Model of Underdrain System August 7 1995 PONDS USER MANUAL 9 2 9 2 LIST OF INPUT PARAMETERS PARAMETER DESCRIPTION SYMBOL Pond amp Stormwater Volume Parameters Treatment Volume PAV cubic feet PAV Area at Top of Pond ATOP square feet ATOP Vertical Distance From Natural Ground or Finished Grade to Pond Bottom ft d Aquifer Parameters Hydraulic Conductivity of Soil K ft day K Depth to Base of Aquifer From Pond Bottom B ft B Drain Parameters Drain diameter D inch D Thickness of gravel envelope above pipe t inch t Depth of soil cover on underdra
80. n of the program to another your license is automatically terminated TERM The license is effective until terminated You may terminate it at any other time by destroying the program together with all copies modifications and merged portions in any form It will also terminate upon conditions set forth elsewhere in the Agreement or if you fail to comply with any term or condition of this Agreement You agree upon such termination to destroy the Program together with all copies modifications and merged portions in any form LIMITED WARRANTY The program is provided as is without warranty of any kind either expressed or implied including but not limited to the implied warranties or merchantability and fitness for a particular purpose The entire risk as to the quality and performance of the program is with you Should the program prove defective you and not Devo Seereeram assume the entire cost of all necessary servicing repair or correction Some states do not allow the exclusion of implied warranties so the above exclusion may not apply to you This warranty gives you specific legal rights and you may also have other rights which may vary from state to state Devo Seereeram does not warrant that the function contained in the Program will meet your requirements or that the operation of the Program will be uninterrupted or error free However Devo Seereeram warrants the diskettes on which the program is furnished to be free from
81. nd and pond bottom R ft R Note usually 0 5 ft or more Background Seepage Ground water baseflow into underdrained pond qb gpm qb August 7 1995 PONDS USER MANUAL E 6 Figure E 3 Cross section of underdrain system showing interpretation of parameters August 7 1995 PONDS USER MANUAL NOTATION continued PARAMETER DESCRIPTION Parameters to Compute Minimum Diameters of Lateral Drain and Main Drain Manning s n Value For Lateral Drain Pipe dimensionless Note n 0 015 for 3 6 diameter ADS corrugated polyethylene pipe n 0 016 for 8 diameter ADS corrugated polyethylene pipe Slope of Lateral Drains 11 96 Note 0 3 to 2 0 recommended for 6 diameter pipe with n 20 015 0 2 to 1 3 recommended for 8 diameter pipe with n 0 015 Maximum Length of Single Lateral Drain ft Manning s n Value For Main Drain Pipe dimensionless Note n 0 015 for 3 6 diameter ADS corrugated polyethylene pipe n 0 016 for 8 diameter ADS corrugated polyethylene pipe Slope of Main Drain I2 96 Note 0 3 to 2 0 recommended for 6 diameter pipe with 0 015 0 2 to 1 3 recommended for 8 diameter pipe with 0 015 Percent of Total Length of Laterals Connected To Main Drain P E 7 SYMBOL n1 n2 August 7 1995 PONDS USER MANUAL E 8 VALIDITY CHECK The ellipse theory is valid when B lt B where Bro Beda s EN 12 24 COMPUTATIONAL STEPS 1 Compute volume of ground
82. off Volume To Be Recovered 100 0 The output results are presented in Exhibit 1 As noted the predicted recovery time for unsaturated and saturated flow is 3 44 days and the radius of influence is 69 5 feet August 7 1995 PONDS USER MANUAL 4 6 EXHIBIT 1 PRINTOUT OF EXAMPLE PROBLEM 1 August 7 1995 PONDS USER MANUAL 4 7 4 5 EXAMPLE 2 DRY BOTTOM RETENTION POND contained in data file EXAMPLE2 DAT The objective of this example is to select the minimum pond bottom elevation which will allow the treatment volume to recover within 3 days 72 hours following a storm event The following are the relevant input parameters Pond Parameters 1 Eguivalent Pond Length E 100 00 ft 2 Equivalent Pond Width 50 00 ft 3 Pond Bottom Elevation to be determined 4 Porosity of Material Within Pond open space 100 0 Aquifer Parameters 5 Base of Aquifer Elevation 22 00 ft 6 Seasonal High Water Table Elevation 23 00 ft 7 Saturated Hydraulic Conductivity horizontal 12 0 ft day 8 Fillable Porosity 26 5 9 Unsaturated Vertical Infiltration Rate Not reguired Runoff Treatment Volume 10 Runoff Volume 3750 0 ft 11 Percent of Runoff Volume To Be Recovered 100 0 The pond bottom elevation is varied interactively on the screen until the recovery time is less than 3 days The output results are presented in Exhibit 2 As noted the predicted recovery time for saturated flow only is 2 99 days for a pond bottom
83. on during the filling of the pond This analytical theory of recovery analysis was developed as part of a research project for the SJRWMD Florida titled Full scale Hydrologic Monitoring of Stormwater Retention Ponds and Recommended Hydro geotechnical Design Methodologies by PSI Jammal Division August 1993 An explanation of the theory is provided in Appendix C of this manual As documented in the SJRWMD funded research report this new methodology has proven to be effective and mathematically stable in predicting the volume recovery of retention ponds It also computes the radius of influence or the distance from the edge of the pond where the water table is unaffected by the recovery of the treatment volume in the pond To be consistent with water management district permitting criteria for recovery of the water quality volume the model does not permit ground water or surface water discharge during the storm event that generates the water quality volume August 7 1995 PONDS USER MANUAL 3 2 This module does not have the capability to compute time varying infiltration during storm events However the Retention Pond Recovery Analysis Refined Method module which is described in the next section has this capability 3 2 2 Module 2 Retention Pond Recovery Analysis Refined Method This is the most powerful module in the PONDS computer program is a true ground water surface water interaction model which simultaneously computes gro
84. ow contributions N is given by 4 FS d min max 10 2 N Therefore the theoretical number of VVRSs reguired is N N and the recommended number of VVRS will be the integer value greater than or equal to N N August 7 1995 PONDS USER MANUAL F 10 REFERENCES Cedergren H R 1977 Seepage Drainage and Flow Nets pp 362 368 2nd edition John Wiley amp Sons New York NY NOTATION average surface area of treatment volume in pond diameter of inner cylinder diameter of outer cylinder safety factor in analysis head at outside edge of filter at some time t maximum driving head through VVRS minimum driving head through VVRS elevation of top of treatment volume elevation of bottom of treatment volume saturated hydraulic conductivity of filter media flow net shape factor for horizontal flow through VVRS recommended number of identical VVRS structures required to recover treatment volume and baseflow contributions theoretical number of identical VVRS structures required to recover treatment volume only theoretical number of identical VVRS structures required to recover baseflow contributions only q instantaneous flow rate through a single VVRS at some time t 4 flow rate from baseflow contributions Qu maximum flow rate through a single VVRS during recovery excluding factor of safety Amn minimum flow rate through a single VVRS during recovery excluding factor of safety T r
85. ow in a Request For Proposal to the project geotechnical engineer SAMPLE REQUEST FORM FOR GEOTECHNICAL SERVICES attached User should provide an information package to geotechnical engineer containing the following 7 Site location 2 Location of stormwater management system within site preferably on site plan With all features such as topographic contours existing drainage ditches wetlands pavqment proposed pond elevations etc Please provide a proposal for a site specific investigation to estimate the hydro geotechnical parameters listed below Based on interpretation of the results of the site specific investigation and experiende with similar soil and ground water conditions we will need your report to recommend appropriate Values and or ranges of input values for the following aquifer parameters D Base elevation of effective or mobilized aquifer ft datum or feet below land surface Weighted horizontal hydraulic conductivity of mobilized aquifer ft day and the project involves recovery analysis of a dry bottom retention pond unsaturated vertical infiltratidn rate ft day For the underdrain option sometimes the pond bottom is excavated into a less permeable soil stratum and it is possible to overexcavate this slowly permeable soil and replace savings in subsurface pipe will justify such an overexcavation and backfill operation Specific yield or fillable porosity of mobilized aquifer 96 Normal seasonal
86. peak stage 105 66 ft peak stage 100 49 ft vol recovered 2 36 hr vol recovered Q 72 hr 11 064 ft 12 584 ft Recovery of water quality volume for dry bottom pond in Example 3 1b including unsaturated infiltration peak stage 100 49 ft vol recovered 36 hr vol recovered Q 72 hr 12 584 ft 12 584 ft August 7 1995 PONDS USER MANUAL 5 25 Table 5 15 Summary of Key Results for Examples 3 1 to 43 9 RESULTS EXAMPLE 3 7 3 8 3 9 APPLICATION Recovery of water quality volume for wet bottom wet detention pond with bleed down device Same as Example 3 1b but higher water table Take into account infiltration during recovery Recovery of water quality volume for wet bottom wet detention pond with bleed down device Same as Example 3 1b but higher water table Not taking into account infiltration during recovery Drawdown of water table due to ditching Determination of required setback distance from wetlands Ambient stage Stage Q Ohr Stage 24 hr Stage 0 48 hr Stage 60 hr Stage 96 hr Ambient stage Stage Q Ohr Stage 24 hr Stage 48 hr Stage 60 hr Stage Q 96 hr 101 50 ft 101 78 ft 101 06 ft 100 69 ft 100 59 ft 100 50 ft 101 50 ft 101 78 ft 101 14 ft 100 72 ft 100 60 ft 100 50 ft Case 1 Impact distance 240 ft SFWMD Impact distance 325 ft SWFWMD Case 2 Impact distan
87. precision which can result from linking dedicated surface water and ground water models It is a true ground water surface water interaction model since the weir discharge module is incorporated directly into the system of finite difference equations solved in MODFLOW This ensures that the conditions of continuity and volume balance are preserved for each time step Another major modification to MODFLOW is the introduction of a stage depedent storage coefficient for the grid cells representing the pond This feature allows the model to August 7 1995 PONDS USER MANUAL D 2 simulate the true stage volume relationship of the pond instead of treating it as a rectangular box Since MODFLOW does not simulate unsaturated flow a separate routine was written by the author to calculate ground water and surface water discharges for unsaturated flow which occurs prior to saturated flow PONDS essentially acts as a pre and post processor to these saturated flow and unsaturated flow calculation routines It allows the user to input parameters and interpret results in formats recognizable to stormwater management design engineers who do not have a working knowledge of MODFLOW PONDS also has a hydrograph generation routine which can create hydrographs using the SCS methodology and facilitate the importation of this input data directly into the model The program can also import hydrographs from the adICPR computer program CONCEPTUAL MODEL A conce
88. ptual model is a pictorial representation of the ground water flow system In the practice of developing a conceptual model it is desirable to strive for parsimony by which it is implied that the conceptual model has been simplified as much as possible yet retains enough complexity so that it adequately reproduces system behavior The conceptual model described hereunder can be applied to the majority of design situations in the state of Florida Figure D 1 illustrates the conceptual stormwater management pond and aquifer system The key elements of this conceptual model are as follows The receiving aquifer system is idealized as a laterally infinite single layered homogenous isotropic unconfined aquifer of uniform thickness with a horizontal pre loading water table The three dimensional shape of the pond is defined by stage area relationship Transient analysis is discretized into an appropriate number of time steps or stress periods Time varying runoff is input in the form of a hydrograph which is a table of elapsed time in minutes versus inflow rate cfs The hydrograph data set also includes a recharge value which can simulate time varying fluctuation of the water table adjacent to the pond during the storm event August 7 1995 PONDS USER MANUAL D 3 Transient lateral saturated flow ground water discharge is modeled using a modified version of the USGS MODFLOW numerical technique The details of the MOD
89. quired to compute the ground water seepage for a 25 year 24 hour design storm event Assume that the project geotechnical engineer hydrogeologist estimates that in the worst case the water table will rise 2 5 feet to an elevation of 103 7 ft during a 2 day period for such a design storm In this example therefore all input parameters are the same as example 4 except for 3 Seasonal high water table elevation H 103 7 ft 4 Rise or fluctuation of water table during study period F 2 5 ft 7 Duration of model period T 2 days The results of this example are included in Exhibit 5 and show a peak ground water inflow of 72 5 gpm Notethat the drawdown of the water table for this short duration event is as follows Distance From Draw Down Or Long Edge of Pond Depression of Water Table 0 ft 3 70 ft 25 ft 1 05 ft 75 ft 0 14 ft 125 ft 0 02 ft August 7 1995 PONDS USER MANUAL 6 6 EXHIBIT 5 PRINTOUT OF EXAMPLE PROBLEM 5 August 7 1995 PONDS USER MANUAL 6 7 6 5 EXAMPLE 6 BASEFLOW INTO POND FROM ROAD UNDERDRAINS contained in data file EXAMPLE6 DAT Assume that in addition to the ground water seepage coming into the pond of example 4 there is a contribution to the pond s baseflow from roadway underdrains in the development which the pond serves The road underdrains have the following dimensions and aquifer parameters in the area where they will be installed 1 Invert elevation of underdrain pipe O 10
90. re the ground water mound is not anticipated to intersect the pond bottom the model setup is different and this toggle must be appropriately set This is mainly used for modeling mounding beneath wastewater percolation ponds and septic leachfields The equivalent pond length and equivalent pond width are used to compute the effective perimeter of the pond These parameters do not affect the storage volume of the pond as in previous versions of the PONDS computer program Refer to the figure on pg 4 4 of the User Manual for the meaning of the effective perimeter parameter August 7 1995 PONDS USER MANUAL 5 14 5 13 EXAMPLE PROBLEMS 5 13 1 Description of Example Problems 18 1 1 General There are a multiplicity of practical applications for the Refined Method module in PONDS However only some of the more common ones in current use are presented here Table 5 5 overviews the ten 10 example problems described in this manual Data files for all ten examples are supplied with the program and file names are included in Table 5 5 reduce the size of this manual neither tabular or graphical printouts of the detailed and sometimes voluminous PONDS output are presented However it is recommended that the user hardcopy the output from the disk files on an as needed basis The user is also encouraged to experiment with the graphical plots of the results 5 13 1 2 Examples 3 1 amp 3 1b As a first step the hydrograph for a 25 yr
91. response to rainfall recharge During the wet season June July August and September 120 days approx it rises from its normal seasonal low level to its seasonal high level It is well known that lateral ground water seepage rates are negligible compared to vertical recharge rates in shallow aquifer regimes in Florida Lateral ground water seepage rates are generally less than 150 feet per year August 7 1995 PONDS USER MANUAL A 2 Depending on the hydrologic soil group slope vegetative cover etc natural recharge to the uppermost aquifer i e rainfall evapotranspiration runoff varies On high water table sites such as Myakka and Smyrna fine sands the rainfall recharge is about 10 to 12 inches during the wet season which is consistent with a 4 feet rise in the water table This assumes a specific yield of 25 for the uppermost aquifer which is reasonable On deeper sands such as Candlers and Astatulas rainfall recharge may be 1 5 to 2 times as high during the wet season resulting in a water table rise of as much as 8 feet This is consistent with the range of seasonal fluctuations typically found on the high and dry sand hills A separate manual has been prepared by the author on estimating the seasonal high water table and its fluctuation and the interested reader may contact the author on how to obtain this manual It will be the geotechnical engineer s or hydrogeologists judgement to select the applicable water table rise i e
92. rily less than the pond bottom area This is important to remember when modeling unsaturated flow in a lined pond In other words the area corresponding to the pond bottom elevation is not counted as available soil storage volume If the water table is very deep and it is not expected that the water table will mound and intersect the pond bottom set this switch accordingly This is useful when simulating the hydraulic loading of wastewater percolation ponds 2 Ditches This feature allows the user to simulate the impact of adjacent ditches The input parameters are the distance from the edge of the pond and the water elevation in the ditch In order to conserve memory and reduce the size of the model the current version of PONDS assumes that an identical mirror image of the ditch exists on the other side of the pond For reasons outlined on the interactive HELP screen it is strongly recommended that this feature not be activated when modeling pond recovery 3 Discharge structures Up to three 3 discharge structures i e weirs orifices can be modeled The interactive HELP screen contains coefficients and exponents for typical discharge structures 4 Stage vs Area This is the stage area data for a pond If a dry bottom pond is being modeled the first stage elevation represents the pond bottom elevation August 7 1995 PONDS USER MANUAL 5 4 Table 5 1 List of Input Parameters Input Parameter
93. stance of the impermeable layer below the pond bottom was not more than twice the width of the water level in the pond August 7 1995 PONDS USER MANUAL C 3 Therefore twice the pond width should be greater than the pond bottom elevation minus the base of aquifer elevation for the theory to be valid The model predicts the time for recovery of the treatment volume and the radius of influence of the hydraulic loading in the pond as derived on page C 1 The computational steps in using the methodology are described below but first the notation is presented NOTATION Pond Parameters Equivalent Pond Length L ft Equivalent Pond Width W ft Pond Bottom Elevation PB ft datum Porosity of Material Within Pond p Note if open pond p 100 if exfiltration trench p lt 100 BM Aquifer Parameters Base of Aquifer Elevation B ft datum Water Table Elevation WT ft datum Horizontal Saturated Hydraulic Conductivity K ft day Fillable Porosity n 96 Vertical Unsaturated Infiltration Rate 1 ft day OPTIONAL Fico Eon Runoff Parameters 11 Runoff Volume V cubic feet 12 Percent Recovery of Runoff Volume PV 96 August 7 1995 PONDS USER MANUAL C 4 COMPUTATIONAL STEPS 1 Compute available volume in soil voids immediately below pond V V L Wn PB WT if PB WT gt 0 V 0 if PB WT lt 0 2 Compute recovery time for unsaturated vertical flow T V es LLW 3 Compute
94. sted in Table 1 1 are installed in the main program directory and the graphics subdirectory August 7 1995 PONDS USER MANUAL 1 4 Table 1 1 List of Files File Name Description PONDS EXE Main Program Executable This file is located in the main program PONDS226 directory MODFLOW EXE ROUTE EXE ROUTE2 EXE ROUTE3 EXE ROUTE4 EXE DRAWDOWN EXE FILTER EXE SEEP EXE UNDER EXE VVRS EXE READDATA EXE SAVEDATA EXE CLEARDATA EXE Subprogram files called by PONDS EXE These files are located in the main program PONDS226 directory MFA EXE BRUN45 EXE SWFWMD EXE UGH256 UHG Shape Factor files used by the Hydrograph Generation UGH323 UHG Module UGH484 UHG These files are located in the main program PONDS226 USER UHG directory CONTINUED ON NEXT PAGE August 7 1995 PONDS USER MANUAL 1 5 Table 1 1 List of Files File Name Description RAIN2MOD RAI Rainfall Distribution Files used by the Hydrograph SFWMD72 RAI Generation Module SJRWMD96 RAI SUWANEE RAI These files are located in the main program PONDS226 ORAN10 RAI directory ORAN25 RAI ORAN100 RAI FDOT1 RAI FDOT2 RAI FDOT4 RAI FDOTS8 RAI FDOT24 RAI FDOT72 RAI FDOT168 RAI FDOT240 RAI USER RAI PDS_1 HLP General Help Files for the PONDS program PDS 2 HLP PDS 3 HLP These files are located in the main program PONDS226 PDS 4 HLP directory PDS 5 HLP PDS 6 HLP PDS 7 HLP PDS 8 HLP PDS 9 HLP CONTINUED ON NEXT PAGE
95. t will be governed by the laws of the State of Florida You acknowledge that you have read this agreement understand it and agree to be bound by its terms and conditions You further agree that it is the complete and exclusive statement of the Agreement between us which supercedes any proposal or prior agreement oral or written and any other communication between us relating to the subject matter of this agreement August 7 1995 GETTING STARTED August 7 1995 PONDS USER MANUAL 1 1 l GETTING STARTED 1 1 REVIEW OF LICENSE AGREEMENT Before you begin it is extremely important that you read and agree to the terms of the license agreement bound in this document You should pay particular attention to the Limited Warranty section If you do not agree to the terms and conditions of the license please return all documentation and diskettes unopened and your money will be refunded 1 2 HARDWARE REQUIREMENTS PONDS Version 2 26 is available on 3 or 5 diskettes for the IBM PC family and other fully compatible machines It requires at least 570 kilobytes RAM memory Although the program will run on any monitor a VGA monitor is required to use the online graphics help screen and to view graphical display of results The following special hardware requirements apply to specific modules Retention Pond Refined Method DOS 3 0 or higher 80386 80486 CPU Intel Math Coprocessor at least 1MB of extended memory Ground water
96. ters Table 5 3 Typical Weir Equations for Free Discharge g cfs CDh Coefficient Dimension Exponent Discharge i C D n Elevation Rectangular weir sharp weir crested Length in ft discharge Rectangular weir broad 2 861 Length in ft weir crested discharge 3 weir Cipoletti trapezoid Length in ft 5 weir discharge Ogee spillway Length in ft tan 0 2 V Notch triangular 0 angle of V notch in degrees vertex of notch T AS orifice Orifice sharp edged Area in ft Orifice rounded 2 Area in ft orifice centroid Orifice short tube Area in ft i orifice centroid Orifice Borda Area in ft i orifice centroid August 7 1995 PONDS USER MANUAL 5 8 5 8 SWFWMD HYDROGRAPH GENERATION MODULE 5 8 1 General The calculation routines for the SCS Unit Hydrograph generation module in PONDS is based on public domain computer code written by Sam Seebali P E and David Sua P E of the Southwest Florida Water Management District Brooksville Florida The hydrograph generator therefores operates somewhat independently of PONDS in terms of data file management The data file which contain the basin parameters used to generate the hydrograph are saved in a separate file such as SWFWMD INP while the detailed hydrograph output is saved separately such as in a file called EXAMPLE HYD The latter file is the one that can be read into the Refined Method module 5 8 2
97. the domain of influence is defined based on simple theoretical considerations and experience with maximum impact distances for the real world systems being analyzed A grid generation routine has been developed to automatically produce a rectangular grid based on pond dimensions equivalent length and width to keep the boundaries of the grid at conservative distances of 1000 to 2000 feet from all sides of the ponds For a width or length dimension of 2 to 3 feet such as a subsurface drain for a road the distance to the boundary is approximately 1000 feet and increases to 2250 feet for pond widths or lengths up to and greater than 700 feet The pond is idealized as an equivalent rectangle occupying the central portion of the model area The model domain is divided into 30 rows and 30 columns with a grid spacing that increases with distance from the edge of the pond and adheres to the conventions on maximum ratio of the spacing of adjacent cells etc Boundary amp Initial Conditions No flow cells are set at the outermost periphery of the finite difference grid This boundary condition allows the water table to rise uniformly in all cells outside the influence of the pond The starting water table is initialized at a uniform level in all cells and is set equal to the wet season elevation minus the anticipated rise during the time specified for the input water table rise such as the duration of a storm event or the entire wet season
98. thm iteratively solves for the stage elevation which satisfies the following volumetric balance Runoff Inflow Discharge Through Weir Unsaturated Infiltration Increase in Storage Schematic D 1 shows the logic of this algorithm This model assumes that unsaturated flow is i only taking place through the bottom area of the pond at an infiltration rate equal to 1 ft day note the bottom area of the pond changes as the water level changes ii purely vertical iii filling the soil voids directly beneath the water surface and iv complete once the soil voids beneath the pond are filled If the inflow rate is faster than the rate at which water can vertically infiltrate through the effective pond bottom water accumulates in the pond If water accumulates in the pond above the weir discharge elevation discharge is modeled using the weir equations This is a relatively simple representation but it is one that is applicable to most cases where the water table is not deep say less than 5 feet below the pond bottom For situations where the water table is over 5 feet below the pond bottom lateral flow can be significant during the unsaturated flow regime but this representation will give conservative results The two input parameters for this module are the vertical infiltration rate for unsaturated conditions and the maximum area available for vertical unsaturated infiltration August 7 1995 PONDS USER MANUAL D 5 SCHEMA
99. ublication titled Fu Scale Hydrologic Monitoring of Stormwater Retention Ponds and Horizontal saturated 1 hydraulic conductivity Recommended Hydro Geotechnical Design of aquifer Methodologies This publication is presently distributed free of charge and may be obtained by calling the SJRWMD library at 1 Fillable porosity of 904 329 4500 ask for Special Publication 5 93 5 10 aquifer Note that the fillable porosity parameter is input in and not in 5 Vertical unsaturated fractions for example 25 and not 0 25 This is a common mistake infiltration rate made by first time users August 7 1995 PONDS USER MANUAL 5 3 Table 5 1 List of Input Parameters Input Parameter Page Description Explanation Maximum area of pond 2 available for unsaturated infiltration Ground water mound intersection switch The volume of soil below a pond depends on the instantaneous water surface area This parameter is the user specified maximum area for computing the available soil storage volume directly below the pond Once this soil storage volume is filled the model simulates saturated lateral flow in which ground water moves laterally away from the pond The user must ensure that the predicted peak stage is not higher than the stage corresponding to the maximum area The pond is assumed to be lined up to the first stage elevation in the stage area data if the input value for the maximum area is arbitra
100. umber of x y points n on the hydrograph 1st line X y note x time in hours y flow rate in cfs X2 Y2 X Yn free format with at least one blank space between x and y data values on the same line The fifth option if to import a Generic ASCII File using the lt F10 gt function key The format for the ASCII file is the same as that as the SWFWMD PONDS hydrograph except it now includes a third column for the outside recharge rate The latter option is used mainly for performing long term hydroperiod simulations where there is a need to model the natural fluctuation of the water table outside the pond 5 6 INTERFACING WITH ADICPR In addition to importing adICPR hydrographs a rating curve of time vs ground water discharge can be exported to AdICPR as an equivalent offsite hydrograph The latter function can be accessed by pressing the lt F12 gt key on the first page of input after the ground water calculations are complete This function key allows the user to create an adICPR offsite hydrograph file for multiple ponds nodes instead of just a single pond 5 7 MODELING OF DISCHARGE STRUCTURES August 7 1995 PONDS USER MANUAL 5 7 Table 5 3 presents typical free discharge weir equations which can be used in the hydrograph routing model The formula is general and many other weirs can be modeled using this equation This table can be viewed on this input screen by pressing the F1 key when inputing these parame
101. und water and surface water discharges during and following transient hydraulic hydrograph loading of a stormwater pond The groundwater component can be deactivated by using a low soil permeability in the routing analysis Saturated ground water flow is simulated using a modified recompiled version of the USGS MODFLOW computer code The two primary modifications which have been made to MODFLOW are as follows new subprogram written by the author has been included to model non linear discharge structures such as unsubmerged weirs orifices notches etc and e Irregular surface area vs stage relationships for ponds are modeled by changing the storage coefficient in the pond as the water level varies Unsaturated flow which may occur prior to saturated flow is modeled using an algorithm written by the author and it is uncoupled from MODFLOW This algorithm has the ability to model perched conditions as well as the increase in the potential ground infiltration rate as the water level stages up and spreads out within the basin Discharge through overflow structures is also modeled during unsaturated flow To the author s knowledge there is no other commercially available computer program which has the true ground water surface water interaction modeling capabilities of the Retention Pond Recovery Analysis Refined Method module The unsaturated and saturated flow models are described in Appendix D PONDS essentially acts as pre
102. ver on underdrain H ft 2 feet Design Criteria Recovery Time T day 3 days Factor of Safety FS dimensionless 2 Minimum distance between water table mound and pond bottom R ft 0 5 feet Background Seepage Ground water baseflows into underdrained pond qb gpm 20 22 gpm Parameters to Compute Minimum Diameters of Lateral Drain and Main Drain Manning s n Value For Lateral Drain Pipe dimensionless 0 015 Slope of Lateral Drains 11 20 0 4596 Maximum Length of Single Lateral Drain ft 200 feet Manning s n Value For Main Drain Pipe dimensionless 0 016 Slope of Main Drain I2 96 0 50 Percent of Total Length of Laterals Connected To Main Drain P 25 As noted on the output in Exhibit 9 the reguired lateral drain spacing is approximately 20 feet and a total lateral drain length of 5118 feet is reguired A lateral drain diameter of 6 inches is adeguate but an 8 inch diameter main drain pipe is needed The outfall will have to accomodate at least 2 67 cfs during recovery of the treatment volume August 7 1995 PONDS USER MANUAL 9 4 EXHIBIT 9 PRINTOUT OF EXAMPLE PROBLEM 9 August 7 1995 PONDS USER MANUAL 9 5 EXHIBIT 9 continued PRINTOUT OF EXAMPLE PROBLEM 9 August 7 1995 APPENDIX A METHODOLOGY FOR ESTIMATING GROUND WATER BASEFLOW INTO PONDS August 7 1995 PONDS USER MANUAL A 1 An Application of MODFLOW To Estimate Ground Water Drawdown Impact Distances and Ground Water Baseflows Into Pon
103. volume to be recovered by saturated lateral flow V V PV V 4 If V lt 0 then stop analysis and report T as recovery time with due to saturated flow as zero Also if PV x V lt V do not perform saturated flow analysis If gt 0 and PV x gt V then continue with saturated analysis following the additional steps outlined below 5 Compute h as V V max Ct PB WT if PB WT gt 0 LxW yes pa hie T if PB WT 0 LxW 6 Compute as V hoin Bmx Tu pLxW 7 Compute initial saturated thickness of aquifer as b WT B August 7 1995 PONDS USER MANUAL C 5 8 Compute recovery time for saturated flow component T using equation 6 on page C 1 9 Compute total recovery time T T T 10 Compute radius of influence substituting hin for h in equation 2 on page C 1 August 7 1995 APPENDIX D MODEL FOR RECOVERY ANALYSIS OF DRY OR WET BOTTOM RETENTION PONDS DURING amp FOLLOWING TRANSIENT HYDRAULIC LOADING August 7 1995 PONDS USER MANUAL D 1 MODELING OF SIMULTANEOUS GROUND WATER AND SURFACE WATER DISCHARGES DURING AND FOLLOWING TRANSIENT VARIABLE RATE HYDRAULIC LOADING OF STORMWATER DETENTION PONDS by Devo Seereeram Ph D P E INTRODUCTION The analytical model of retention pond recovery described in Appendix C of this manual assumes that the runoff volume instantaneously fills the pond This assumption is appropriate for t
104. w pit dewatering and ground water seepage into roadway underdrains ditches interceptor trenches etc It is also useful for assessing potential wetland dehydration impacts The baseflow seepage methodology was developed by the author and is described in Appendix A of this manual The USGS MODFLOW model performs the transient ground water flow calculations although the user never interfaces directly with the MODFLOW program A working knowledge of MODFLOW is NOT required to run the program All input parameters are comprehensible to a lay engineer hydrologist Users will find a number of real world applications for this flexible dewatering program other than those mentioned above 3 2 5 Module 5 Calculation of the Length of Side Bank amp Bottom Filter This module calculates the length of side bank or pond bottom drain filter required for retention ponds that treat stormwater with filtration systems The theory of the analysis is based on a closed form analytical adaptation of the falling head equation derived by the author The filter detail includes a gravel envelope around the drain pipe which is consistent with the latest St Johns River Water Management District SJRWMD Florida criteria For the interested reader a paper describing the theoretical basis of the side bank pond bottom filtration model is included in Appendix B This module also allows for the automatic inclusion of ground water baseflow in computing the required length of
105. within these cells due to the high hydraulic conductivity and the approximation to the second derivative is zero see explanation on page 64 65 of Anderson and Woessner 1992 Boundary amp Initial Conditions As mentioned previously specified head boundaries are set along Row 1 and Column 60 of the finite difference mesh These fixed heads are set at the input value of the water table elevation No flow cells are set along the axi symmetric boundaries i e Row 60 and Column 1 of the grid All other nodes within the grid are free to vary during the simulation Within the cells representing the pond however the heads are also influenced by the discharge through the weirs or orifices which are akin to MODFLOW DRAINS with a non linear head vs discharge relationship The heads in the variable head cells outside the pond are initialized to the input water table elevation On the other hand the heads in the variable head cells within the pond are initialized to the pond bottom elevation if the ground water mound is expected to intersect the pond bottom There is an option for setting the initial head within the pond cells to the input water table elevation if the unsaturated flow option is not activated Hydrostratigraphic Idealization and Parameters August 7 1995 PONDS USER MANUAL D 8 The MODFLOW model is a 1 layered system which requires specification of the following water table aquifer parameters Horizontal saturated hydrau
106. y to a closed form solution which is a falling head variant of the theory of horizontal flow through vertical sand drain wells presented previously by Cedergren 1977 The variables in the derived formula are 1 the inside and outside diameters of the hollow cylindrical filter 2 volume and maximum amp minimum stage elevations of treatment volume 3 desired recovery time 4 tailwater elevation of receiving water body and base elevation of VVRS 5 hydraulic conductivity of filter media and 6 factor of safety The theory also include allowances for direct and indirect ground water baseflows into the pond Equations are also presented for computing maximum flow rates per structure to ensure outfall pipes are properly sized August 7 1995 PONDS USER MANUAL F 2 DESCRIPTION OF VVRS Typical Detail Figure F 1 shows a typical construction detail for a vertical hollow cylindrical sand filter or VVRS The VVRS consists of two concentrically and vertically placed perforated aluminum pipes which are set on a concrete base Although not shown on this typical detail it is recommended that future design details include geonets on the inside face of the outer cylinder and the outside face of the inside cylinder to ensure horizontal flow through the entire submerged area of the sand filter The diameters of the inside and outside pipes are selected to provide a minimum annular space of 2 feet Inside diameters are typically about 2 feet

PONDS Version 2.26 Users Manual.

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