INTRODUCTION TO MODRET
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 once again totally redesigned and greatly improved. Similar to Version 5.0, the MODRET Version 6.0, For Windows 95, 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. In addition, this version includes a pond routing module which allows routing runoff through a pond allowing for infiltration losses and determination of peak discharge rate and peak water elevation. This version is fully compatible with all Windows 95 environments which allows flexibility in data management as well as text and graph generation on any compatible printing or plotting device. MODRET Version 6.0, For Windows 95, is used for permit reviews by the SWFWMD, SJRWMD, FDOT, FDEP and other regulatory agencies.
The new model capabilities, 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. The user's guide was designed in a graphical/schematic format to allow quick access to the material and find the answers to questions. 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 & Harbaugh, 1984, to calculate saturated infiltration.
It is assumed the user is a professional with a background in hydrology and/or hydrogeology and has a good command in surface runoff and groundwater flow modeling. It is also assumed that the user is familiar with the use of personal computers and the Windows 95 operating system and its environment.
WHAT'S NEW IN MODRET VERSION 6.0
The new MODRET, Version 6.0, For Windows 95, program was completely revamped and reprogrammed in the object-oriented Windows 95 environment. Similar to the Version 5.0, the model is capable of generating runoff hydrographs by various methods and for fixed or user-specified rainfall distribution data. A new addition to this version is the routing module which was not available in previous versions. The routing module allows determination of peak discharge rates and peak water elevation in the ponds using runoff, infiltration and stage-storage data. The MODFLOW model is a modified version that allows weir flow and orifice flow from retention ponds. A brief description of the four modules of MODRET follows:
Hydrograph: 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 20 options of which 18 are fixed distributions (selected SCS, FDOT and other Florida distributions) and the last two are changeable distribution options which can be specified by the user. The limitations of this module are 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 hydrograph from other models such as AdICPR TM, SMADA, CHAN or other similar commercially available models. The graphical presentation of the hydrograph is limited to about 800 data points; therefore, excessively long duration storm events, i.e., 240 hours, cannot be graphically displayed by MODRET. However, the runoff hydrographs will be properly created and used in the modeling.
Infiltration: This module is the main part of MODRET which includes a pre-processor and a post-processor procedure to enter the pond, weir and aquifer characteristics; calculate unsaturated infiltration; setup MODFLOW data files; execute the MODFLOW program for saturated infiltration; read the results, and calculate and display the results. The input of runoff can be done by simply specifying the file name of the corresponding runoff hydrograph, entering total runoff volume and recovery time, or entering the runoff manually one time increment at a time. After calculation of infiltration losses, the runoff hydrograph can be routed through infiltration and a new "Runoff-Infiltration" hydrograph can be generated which can then be reused in other surface runoff routing models. This option is useful when modeling complicated and/or interconnected ponds. The runoff hydrographs can be generated for each pond, individual infiltration analysis can be performed for each pond and "Runoff-Infiltration" hydrographs can then be exported for continuation of modeling of the ponds. 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 discharge relationship (rating curve). The presentation of the output data can be in a tabular and/or graphical format, and it is presented in a report-quality output.
Routing: This is a new module for MODRET which completes the capability of the model to generate runoff hydrographs, calculate infiltration losses and then route the runoff through the pond using actual stage-storage data of the pond. The routing module allows determination of maximum (peak) discharge rate for the storm event and the maximum stage (water elevation) for the pond. The user specifies the stage-storage data for the pond, and the model utilizes the small time increments of the runoff hydrograph to calculate the incremental discharge and water elevation. In addition, the module produces graphical summaries for total runoff, runoff-infiltration, cumulative infiltration, cumulative discharge volume, instantaneous discharge rate and water elevation.
Graphics: This module allows for creation of data files and graphical files for presentation of model results. This module can create an XYZ file, a runoff-infiltration file and a cross section file. An XYZ data file can be generated for the groundwater elevations around the retention pond which can be imported into SURFERTM, AutoCadTM, MathCadTM , or other contour/3D-view generating models for evaluation of groundwater mounding around the pond. The module has only one graphical display option, "the Cross-Section Graphic," which displays a series of cross sections of groundwater elevations through the retention pond along 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 groundwater mounding within, and in the vicinity of, the retention pond. The location and extent of the cross section can be specified by the user.
MODRET HARDWARE AND SOFTWARE REQUIREMENTS
For the set up and execution of the MODRET model, the following minimum equipment and software is required:
A personal computer running Windows 95/98/2000.
A minimum of 8MB RAM.
An SVGA card and a compatible monitor.