Application of a Water Balance Model and GIS for Sustainable Watershed Management

Abstract

Chester County, Pennsylvania is one of the fastest growing areas in the Country, and is experiencing significant environmental impacts due to suburban sprawl. Northern Chester County is a relatively undeveloped area, but is rapidly experiencing the pressure of encroaching development. This scenic and historically significant area is dependent on ground water for water supply and is traversed by four high quality or exceptional value streams of great environmental and recreational importance to the region. In Pennsylvania, regulations regarding stormwater management and water resources are enacted at the local or municipal level. Municipal boundaries rarely coincide with watershed boundaries, making effective watershed plans difficult to implement. To overcome this difficulty, the municipalities are working together with Green Valleys Association to develop a Watershed Management Program. At the heart of this program is a Water Balance Model, interactively linked to a detailed GIS developed in ArcInfo and ArcView. This tool allows the municipalities to play what scenarios and determine if the sustainable watershed goals are attainable, or if changes are needed in municipal regulations. For example, if current zoning allows for a certain type of development on a given parcel, the municipality can examine the effects of that development on water withdrawals, stormwater runoff and non-point source pollution, groundwater nitrate levels, and baseflow in the streams. The model evaluates conditions on a watershed basis, but allows for interpretation on a municipal basis. If the sustainability criteria are not met, the municipality can then look at the effects of changes in ordinances, changes in zoning, transferdevelopment rights, etc. The visual component of the GIS allows the planners and municipal officials to quickly see the areas of concern, as well as the effects of regulatory changes. Most importantly, theinteractiveGIS/model helps non-technical residents and decision makers to understand the inter-relationship between land use and water resources, and to make educated policy decisions accordingly. Introduction Sustainable Watershed Management Sustainable Watershed Management (SWM) has been developed by the Green Valleys Association (GVA) to guide the management of the special land and water systems that comprise northern Chester County watersheds. The primary goal is to sustain the essential environmental qualities that distinguish this region, and the values held so strongly by the local community. It is the goal of GVA that when the wave of development pressures