Infiltration from stormwater retention ponds using MODFLOW - runoff hydrographs



MODRET (Computer MODEL to Design RETENTION Ponds) was originally developed in 1990 as a complement to a research and development project for the SWFWMD. The scope of this project was to develop a practical design manual for site investigation criteria, laboratory and field testing requirements and guidelines to calculate infiltration losses from stormwater retention ponds in unconfined shallow aquifers. Since 1990, there have been several revisions to the original model consisting of more options and greater flexibility. For this revision, the model was totally redesigned and greatly improved. MODRET Version 5.0 allows generation of runoff hydrographs with various methods, calculation of infiltration losses from a retention pond, discharge (overflow) through various types of weirs and orifices, and generation of graphical results that are suitable for inclusion in final design reports for presentation and permitting. MODRET Version 5.0 is used for permit reviews by many regulatory agencies.

The MODRET Version 5.0 computer program was developed with many new options and user-friendly data input and output. The program is menu-driven and incorporates tabular and graphical output of results ready to be included in design reports. The new options, data entry, and output formats were developed based on many comments and recommendations submitted by the users of previous versions of MODRET.

The user's guide was developed to allow detailed explanations of the model menu screen prompts to assist the "first time" user in understanding the conventions and functions of each prompt. It was designed in a graphical/schematic format to allow quick access to the material and find the answers to questions. This version of MODRET has a new module that generates runoff hydrographs using three types of methods: the SCS Unit Hydrograph, the Rational Hydrograph, and the Santa Barbara Urban Hydrograph methods. The Infiltration Module of the program uses a modified Green & Ampt infiltration equation to calculate unsaturated infiltration and a modified USGS model "A Modular Three-Dimensional Finite-Difference Ground-Water Flow Model," McDonald and Harbaugh, 1984, to calculate saturated infiltration.

The user is assumed to be a professional with a background in hydrology and/or hydrogeology and have a good command in surface runoff and ground-water flow modeling. It is also assumed that the user is familiar with the use of the microcomputer and its environment.

The new MODRET Version 5.0 program was completely revamped and reprogrammed in a new environment. The model now consists of three modules which are run from a menu-driven environment with graphical displays, direct execution of external programs, and generation of report-quality tabular and graphical results. The model is now capable of generating runoff hydrographs by various methods and for fixed or user-specified rainfall distribution data. The MODFLOW model was modified to allow weir flow and orifice flow from retention ponds which has increased the flexibility of this model. A brief description of the three modules of MODRET follows.

Hydrograph Module: This module allows generation of stormwater runoff hydrograph using the SCS Unit Hydrograph, the Rational Hydrograph, and the Santa Barbara Urban Hydrograph methods. The rainfall distribution data are selected from a list of 15 options of which 13 are fixed distributions and the last two are changeable distribution options which can be specified by the user. The limitations of this module is that it can only generate a runoff hydrograph for a single watershed. However, the Infiltration Module of MODRET (described below) was developed to accept runoff hydrographs from other models such as AdICPRTM or other similar commercially-available models.

Infiltration Module: This module is the main part of MODRET which includes a preprocessor and postprocessor, procedures to enter the pond, weir and aquifer characteristics, calculate unsaturated infiltration, set up MODFLOW data files, execute the MODFLOW program, read the results, calculate and display the results, and create graphical data files to be used by the Graphics Module. The input of runoff volumes into the infiltration module can be accomplished by simply specifying the file name of the corresponding runoff hydrograph or manually entered one time increment at a time. After calculation of infiltration losses, the runoff hydrograph can be routed through infiltration and a new "routed" runoff hydrograph generated which can then be reused in other pond routing models. The MODFLOW model was specifically modified for use with the MODRET model which incorporates modeling of weir and orifice overflow or overflow based on manually-specified elevation vs. flow relationship (rating curve). The presentation of the output data can be in tabular and/or graphical format and is presented in report-quality output. The volumetric runoff hydrographs are graphically presented, and the total volumes of the original and the routed hydrographs and the infiltrated water are calculated and presented with the graphical output. The peak discharges and time of peak are calculated for both the original hydrograph and the infiltration routed hydrograph. In addition, an XYZ data file can be generated for the ground-water elevations around the retention pond which can be imported into SURFER, AutoCAD, or other contour/3D-view generating models for evaluation of ground-water mounding around the pond.

Graphical Module: This module is intended to read graphical data files previously created by the Infiltration Module and display the results for review, evaluation and/or printout of a hard copy for inclusion in a report. This module has two graphical display options. The Cross-Sectional Graphic displays a series of cross sections of ground-water elevations through the retention pond along the X and Y axes. The X and Y axes originate at the center of the pond. This option allows a quick review of the shape and extent of ground-water mounding within (and in the vicinity of) the retention pond. The second option displays a graphic with cumulative runoff and infiltration vs. time during a design storm event. This option is possible only if the modeling included the use of a runoff hydrograph for the recharge input option. For manual recharge specification, this option can not be used as there is not a hydrograph to display. To graphically display the water elevation vs. time and the cumulative infiltration losses for all input options, the graphical display option within the Infiltration Module can be used.

After input of all data, the hydrograph generation model is automatically executed and the results are saved. The input data is also saved automatically. However, if some changes to the input data file are made, the changes can be saved by selecting SAVE in the FILE option. The input data can be printed or viewed with the VIEW option allowing a graphical view of the generated hydrograph or another hydrograph (if a new hydrograph file name is specified). Once the hydrograph is presented graphically, this option also allows printout of the graphical runoff hydrograph.

MODRET Requirements: 486/Pentium with 4 MB RAM.

Incredible NetworksΤελευταία Ενημέρωση 27 Ιουλίου 2004 - Last Revised on July 27th 2004
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