Use of Geographic Information Systems (GIS) in urban storm- water modeling is a growing technology designed for storing, manipulating, analyzing, and displaying data in a geographical context. It can be characterized as a software package that efficiently relates geographic information to attribute data stored in a database. While GIS has been around since the 1960s (Tsihrintzis et al. 1996), it is only with the emergence of personal computers in the 1970s that it has found widespread use. A full realization of the potential of GIS awaits standardized and more accessible databases.
Urban nonpoint pollution produces stormwater that is polluted with, for example metals, pesticides, and nutrients due to land useand urban activities throughout the urban environment (Haubner and Joeres 1996; Soonthornnonda et al. 2006). The polluted storm water is a major source of contamination of our water resources. GIS can be an effective tool for storing, managing, and displaying spatial data often encountered in water resources management (Tsihrintzis 1996). Previously, the process of watershed modeling meant the study of maps and documents to collect information on land use, soil types, elevation, and piping network for a particular drainage area. This process is very tedious and labor intensive. Using spatial data to gather information about the study area is often more advantageous. Not only does this process facilitate examination of a wider range of alternatives for routing and treatment of storm water, but also provides an interactive management framework that can be modified and updated once the watershed conditions are changed (Xu et al. 2001).
Land use maps, digital elevation models (DEMs), soil imperviousness information maps, contours, 2D and 3D elevation maps, digital orthographic aerial photos, and piping network maps of the drainage area can be used to generate input parameters for an urban storm-water model. Fig. 1 shows an example of a GIS map containing contour and land use information.
Fig. 1. (Color) Map of an urban storm-water drainage area in Milwaukee county, Wisconsin showing land use and contours. Contour elevations indicate meters above sea level. Data are from MMSD (2006), SEWRPC (2000), and USGS DEMs (2000). See text for abbreviations.
GIS maps can be geocoded and georeferenced to a base data layer (Haubner and Joeres 1996). GIS data can be procured from GIS data clearinghouses, e.g., GIS Data Depot, and Geospatial One Stop, available on the internet. One should keep in mind that a major hurdle in using GIS technology is obtaining the right kind of data. GIS data mainly consist of shapefiles which can show spatial features of the terrain. There are other files such as database files and project files which supplement these shapefiles. Land use GIS maps can be generated using data from regional and local agencies. In the case of Fig. 1, regional land use data were obtained from SEWRPC (2000). This data is usually in vector format, e.g., point, polygon, and line. DEMs are useful in understanding the elevation of the surface terrain. DEMs have raster grids which are composed of regularly spaced elevation values which are derived from the United States Geological Survey (USGS) topographic map series (USGS DEMs 2000). Vector and raster data are the two most important types of GIS data. DEMs can be used to generate 2D and 3D maps showing the natural terrain. Contour maps can also be generated from DEMs (Fig. 1). Soil imperviousness can be generated from IKONOS satellite images using various statistical techniques such as Fisher Discriminant Analysis (Herold et al. 2003). Aerial photographs show a bird’s eye view of the study area. The National Aerial Photography Program and the National Agricultural Imagery Program are good sources for aerial photos. Piping network data for a particular drainage area are clearly important for understanding runoff pathways, and they can be derived from hardcopy maps. These hardcopy maps can be scanned, digitized, and georectified. Computer aided drafting (CAD) programs in AutoCAD or Microstation can be used to create CAD drawings of the piping network, which can then be georectified and overlaid on the drainage area maps. Also, a GIS database of rainfall readings, measured pollutant concentrations, or other parameters can be created and maintained using GIS software Arc Desktop and Arc View (Environmental Systems Research Institute). GIS overlay and data manipulation capabilities can be utilized to preprocess the input data for the model (Haubner and Joeres 1996).
Georeferencing is an important factor in using GIS to map areas and their characteristics. All maps, e.g., land use, soil types, elevation, and piping network, must be geographically compatible with each other. In other words, they must have the same map coordinate system. Arc Desktop and Arc View extensions, such as Spatial Analyst and 3D Analyst, can be used to develop and manipulate spatial relationships between different spatial data types. Thus GIS analyses can be done to understand the changing spatial patterns of urban growth. The Storm-Water and Wastewater Management Model is one such storm-water management model that can be integrated with GIS in order to determine the volumetric runoff and contaminant loadings of storm water. Also, the integration of remote sensing and GIS can be applied to automate the estimation of surface runoff based on the soil conservation service model (Weng 2001).
Along with storm water runoff determination, GIS can also facilitate better understanding of the drainage pattern of the study area. Sometimes drainage areas may be overestimated or underestimated depending upon lack of spatial information. Soil imperviousness data, piping network information, elevation, land use, and other factors can facilitate a more accurate estimation of drainage areas. In Fig. 1, the Milwaukee Metropolitan Sewerage District (MMSD) provided the monitoring site and the suggested drainage area (MMSD 2006). Best management practices (BMPs) may be applied to minimize storm water runoff and associated pollution problems. BMP performance varies from site to site and season to season. GIS allows managers to evaluate impacts of various BMPs with given hypothetical conditions (Wong et al. 1997). GIS can be used to study the effective scenarios of the BMPs depending on each characteristic, e.g., storm water quality, storm water quantity, runoff pattern, piping network, and percentage of soil imperviousness of the drainage area. Furthermore, an integrated set of tools can be developed from the modeling programs that can interact with GIS. Such a system is called a Decision Support System (DSS). Sample et al. (2001) suggest that the best use of GIS in urban storm-water modeling is when it is integrated into a DSS.
Recommendations
To make GIS a more prominent feature in urban storm water modeling, urban storm-water engineers have to work with GIS specialists and eventually be trained by them. National and regional level GIS repositories need to be created which can be updated from time to time. These data repositories have to be accessible at the local as well as national level. To keep the privacy issue at bay these repositories need to identify the right users. Sensitive information should not be released without prior consent and fulfilling legal aspects between data managing bodies and end users. For example, ASCE can work with USGS, the United States Environmental Protection Agency (USEPA), and the National Oceanic and Atmospheric Administration (NOAA) to make data files more compatible and accessible. GIS files should always be compatible with updated data managing and processing software such as Microsoft Access and Microsoft Excel. A central body at the national level needs to be established to issue guidelines for local agencies to standardize their GIS data and capabilities. State and county level agencies managing GIS data such as Wisconsin Department of Natural Resources and SEWRPC should interact with USEPA to make their GIS data more accessible. Overall, GIS use in the field of storm water modeling has tremendous potential to be a front runner in the technological advancements of the twenty-first century. We as engineers need to fully tap this potential.
References
Haubner, S. M., and Joeres, E. F. (1996). “Using a GIS for estimating input parameters in urban stormwater quality modeling.” Water Resour. Bull., 32(6), 1341–1351.
Herold, M., Liu, X., and Clarke, K. C. (2003). “Spatial metrics and image texture for mapping urban land use.” Photogramm. Eng. Remote Sens., 69(9), 991–1001.
Milwaukee Metropolitan Sewerage District (MMSD). (2006). “Expanded stormwater monitoring program data analysis 2000–2006.” Facilities Information Division, Milwaukee, Wis.
Sample, D. J., Heaney, J. P., Wright, L. T., and Koustas, R. (2001). “Geographic information systems, decision support systems, and urban storm-water management.” J. Water Resour. Plann. Manage., 127(3), 155–161.
Soonthornnonda, P., Seth, I., Liu, Y., Li, J., and Christensen, E. R. (2006). “MMSD expanded stormwater monitoring program” 1st Interim Rep., Dept. of Civil Engineering and Mechanics, Univ. of Wisconsin, Milwaukee, Wis.
Tsihrintzis, V. A., Hamid, R., and Fuentes, H. R. (1996). “Use of Geographic Information Systems (GIS) in water resources: A review.”Water Resour. Manage., 10, 251–277.
Weng, Q. (2001). “Modeling urban growth effects on surface runoff with the integration of remote sensing and GIS.” Environ. Manage. (N.Y.), 28(6), 737–748.
Xu, Z. X., Ito, K., Schultz, G. A., and Li, J. Y. (2001). “Integrated hydrologic modeling and GIS in water resources management.” J. Comput. Civ. Eng., 15(3), 217–223.
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