KEY TERMS: BMP; pre-processor; post-processor; pollutant loads;
modeling; watershed management
Introduction
Best management practices (BMPs) as stormwater control systems
are widely used in agricultural and urban areas to prevent
flooding, reduce soil loss, provide water retention, and most
importantly reduce pollutant loadings to receiving water bodies
(Chen et al., 1995). BMP performance varies from site to site and
season to season. A user-friendly tool is needed to evaluate the
performance of BMPs, project future stormwater quantity and quality
in drainage systems, and identify key design parameters to improve
BMP pollutant removal efficiencies.
The Best Management Practices Assessment Model, BMPAM (Xue, 1995a), developed for evaluating the performance of various BMPs, was selected for this tool. A user-friendly interface for BMPAM was developed using a geographic information system (GIS) platform. Integration of GIS and BMPAM reduces the tedious work of data formatting and allows easy interpretation of model inputs and simulation results. This integrated GIS tool can analyze stormwater treatment systems and water resources management plans for a single watershed or a large-scale basin.
This paper describes the conceptual design of the integrated
GIS and the BMPAM model developed at the South Florida Water
Management District (SFWMD). This integrated tool was implemented
using ArcView version 2.1 software and its AVENUE language, which
provides the linkage between data coverages, pre-processor, the
BMPAM model, and post-processor. An example application was
included to demonstrate the tool's potential uses and capabilities.
Integrated Tool Development
The BMPAM model, input and output data, pre- and post-
processors, and the GIS-BMPAM interface are key components of the
integrated GIS tool. GIS provides all required information to the
other components. The input data component links with the pre-
processor via the GIS user interface. Data from the pre-processor
is fed into the BMPAM model. The model is executed through a
system command in the GIS interface. The post-processor component
displays model simulation results in various tabular and graphic
formats through the GIS user interface. Files generated by the
pre-processor and the BMPAM model are stored by the system for
reuse or modification through the GIS user interface or other
UNIX/DOS operating system utilities. This conceptual design is
similar to that applied to an integrated watershed model-GIS
system presented by Xue and Bechtel (1996).
ArcView 2.1 allows developers to customize applications using AVENUE, an object-oriented scripting language (Hutchinson and Daniel, 1995). Customized ArcView interface features include bars (i.e., menu, button, tool, and status bars), pulldown menus, and pop-up windows. For example, three customized menus appear when a user opens the integrated GIS tool in an ArcView window: (1) Pre- processor; (2) Run Model; and (3) Post-processor. Each menu contains pulldown menus customized for the tool.
The first menu item enables users to select the type of BMPs to be simulated (figure 1). Three types of BMPs are available in this integrated tool: (1) Detention Basin (e.g., wet detention pond, dry detention pond, and wet extended detention pond); (2) Retention Device (e.g., infiltration trench, dry well, and porous pavement); and (3) Vegetative Control (e.g., wetland, grassed swale, and filter strip). Once a BMP type is selected, users input physical and hydraulic parameters for the selected BMP from the second menu item: (1) depth and surface area, (2) initial water elevation, (3) water elevation above weir, (4) weir coefficient and width; and (5) size of the upstream drainage area (figure 2).
Figure 1. -- BMP Type Selection Screen in the Pre-Processor
Figure 2. -- Hydraulic Parameters Input Screen in the Pre-Processor
The integrated GIS tool allows users to simulate three infiltration layers for BMPs. Infiltration parameters for each layer, such as maximum and minimum infiltration rate, decay parameter, infiltration regeneration ratio, area, depth, and porosity are input in the third menu item. Initial pollutant concentration and decay rates are input in the fourth and fifth menu items, respectively (figure 3). For simulation of particles/solids, users can specify up to five particle classes and enter percentage, diameter, and specific gravity of each class in the Input Particle Parameters menu item.
Figure 3. -- Pollutant Decay Data Input Screen in the Pre-Processor
To simulate wetlands and other vegetative control practices, users need to provide microphyte and macrophyte information. In the seventh menu item, required data are monthly coefficients for plant uptake of nutrients (figure 4). The last menu item saves all entered selections and data. Meteorological data such as precipitation and evaporation are pre-stored in the integrated GIS system.
Figure 4. -- Monthly Macrophyte Data Input Screen in the Pre-Processor
The first menu item allows users to compare Pre-BMP and Post-
BMP simulation results for either runoff or a pollutant
constituent. The second menu item asks users to choose two
parameters for Post-BMP display. The third and fourth menu items
enable users to define the hourly and daily period of simulation
results, respectively. The next two menu items allow users to
display the hourly, daily, monthly, and annual simulation results
for Post-BMP only and comparison of Pre-BMP and Post-BMP,
respectively. Hourly and daily simulation results are plotted on
line charts, whereas the monthly and annual results are plotted on
bar charts. Tabular results of all displays described above also
are available through the Post-Processor.
An Example Application
As an example, the integrated GIS tool was used to evaluate
nutrient removal efficiency for a hypothetical wet detention pond.
The surface area and the storage depth of the pond were 6070 m2
(1.5 acres) and 0.9 m (3 feet), respectively. The pond had one
natural infiltration layer and nutrient uptake by plants was not
considered. The wet detention pond received runoff from a farm in
Okeechobee County, Florida with drainage area of 631,632 m2 (156
acres).
Runoff and associated total phosphorus loads from the drainage area were obtained from a catchment-scale Stormwater Runoff and Pollutant Model, SRPM (Xue, 1995b, Xue and Zhang, 1996). The simulation results consist of a 2-year calibration (1990-1991) and a 3-year verification (1992-1994). Precipitation and evaporation data were obtained from Xue and Zhang (1996). Input data for BMPAM was accessed through the integrated GIS tool's pre-processor. The BMPAM model was run continuously for a five-year period at hourly time steps.
Simulation results are viewed via the tool's post-processor. Hydrographs for pre- and post-BMP conditions (figure 5 and figure 6) show a significant reduction and delay of runoff peak for the post-BMP conditions. Hourly and daily pollutographs also are viewed via the Post-Processor (Figures 5 and 6, respectively). Figure 7 presents monthly simulation results of runoff and total phosphorus loads in 1993 after application of the BMP. Annual comparison results for pre- and post-BMP conditions exhibit a significant reduction of total phosphorus loads after application of BMPs (figure 8).
Figure 5. -- Simulated Hourly Runoff Before and After BMP
Figure 6. -- Simulated Daily Runoff Before and After BMP
Figure 7. -- Simulated Monthly Runoff and Total Phosphorus Loads After BMP
Figure 8. -- Simulated Annual Total Phosphorus Loads Before and After BMP
Summary
An integrated GIS tool for evaluating stormwater BMPs was
developed using the ArcView software with its object-oriented
scripting language, AVENUE. The integrated GIS tool incorporates
hydrologic and water quality input data, a BMP model, and
simulation output via three key functions: Pre-processor, Run
Model, and Post-processor. The integrated tool allows users to
easily run the BMPAM model without knowing input data formats and
to display simulation results in tabular and graphic forms. The
integrated GIS system provides watershed managers and planners with
a user-friendly and powerful tool to analyze the effectiveness of
different BMPs.
References
Chen, Z., M. Lahlou, R. Z. Xue, and M. S. Cheng, 1995. An Integrated Impact Assessment Model for Urban Watershed Planning. Proceedings of the 4th Biennial Stormwater Research Conference. Southwest Florida Water Management District, Brooksville, Fl., pp. 53-62.
ESRI Inc., 1994. Introducing ArcView. Environmental Systems Research Institute Inc., Redlands, CA.
Hutchinson, S. and L. Daniel, 1995. Inside ArcView. Santa Fe, NM:OnWord Press.
Xue, R. Z., 1995a. Best Management Practice Assessment Model - BMPAM Model Documentation (Draft). South Florida Water Management District, West Palm Beach, FL.
Xue, R. Z., 1995b. Stormwater Runoff and Pollutant Model - SRPM Model Documentation (Draft). South Florida Water Management District, West Palm Beach, FL.
Xue, R. Z. and T. Bechtel, 1996. Predicting Stormwater Runoff and Pollutant Loads Using an Integrated GIS Tool. Proceedings of GEOINFORMATICS'96 - International Symposium on GIS, Remote Sensing Research, Development and Applications. South Florida Water Management District, West Palm Beach, Fl., Volume 2, pp. 377-385.
Xue, R. Z. and J. Zhang, 1996. Application of SRPM to Predict Stormwater Runoff and Phosphorus Loads. To be presented at the AWRA Annual Symposium of Watershed Restoration Management: Physical, Chemical, and Biological Considerations, July 14-17, Syracuse, NY.
Acknowledgements
The authors gratefully appreciate the comments of Wossenu
Abtew, Larry Fink, Susan Gray, Weihe Guan, Steve Lin, Garth
Redfield, Douglas Shaw, and Todd Tisdale for this paper.
2.
Timothy J. Bechtel
Senior Environmental Scientist
Department of Water Resources Evaluation
South Florida Water Management District
3301 Gun Club Road
West Palm Beach, Florida 33416
Telephone:(561) 687-6392
Fax:(561) 687-6442
3.
Zhenquen Chen
Senior Civil Engineer
Department of Ecosystems Restoration
South Florida Water Management District
3301 Gun Club Road
West Palm Beach, Florida 33416
Email:zhen.chen@sfwmd.gov
Telephone:(561) 687-6552
Fax:(561) 687-6442
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