Assessing the Long-Term Hydrologic Impact of Land Use Change Using a GIS-NPS Model and the World Wide Web

摘要

Assessment of the long-term hydrologic impacts of land use change is important for optimizing management practices to control runoff and non-point source (NPS) pollution associated with watershed development. Land use change, dominated by an increase in urban /impervious areas, can have a significant impact on water resources. Non-point source (NPS) pollution is the leading cause of degraded water quality in the US and urban areas are an important source of NPS pollution. Despite widespread concern over the environmental impacts of land use changes such as urban sprawl, most planners, government agencies and consultants lack access to simple impact-assessment tools that can be used with readily available data. Before investing in sophisticated analyses and customized data collection, it is desirable to be able to run initial screening analyses using data that are already available. In response to this need, we developed a long-term hydrologic impact assessment technique (L-THIA) using the popular Curve Number (CN) method that makes use of basic land use, soils and long-term rainfall data. Initially developed as a spreadsheet application, the technique allows a user to compare the hydrologic impacts of past, present and any future land use change. Consequently, a NPS pollution module was incorporated to develop the L-THWNPS model. Long-term daily rainfall records are used in combination with soils and land use information to calculate average annual runoff and NPS pollution at a watershed scale. Because of the geospatial nature of land use and soils data, and the increasingly widespread use of GE by planners, government agencies and consultants, the model is linked to a Geographic Information System (GIS) that allows convenient generation and management of model input and output data, and provides advanced visualization of the model results. Manipulation of the land use layer, or provision of multiple land use layers (for different scenarios), allows for rapid and simple comparison of impacts. To increase access to L-THIA, we have begun development of a WWW-accessible version of the method. Using databases housed on our computers, the user can select any location in the US and perform L-THIAINPS analyses. In this paper we present applications of the WWW-based L-THIA/NPS and L-THIA/NPS GIS model on the Little Eagle Creek (LEC) watershed near Indianapolis, Indiana. Three historical land use scenarios for 1973, 1984, and 1991 were analyzed to track land use change in the watershed and to assess the impacts of land use change on annual average runoff and NPS pollution from the watershed and its five sub-basins. Comparison of the two methods highlights the effectiveness of the L-THIA approach in assessing the long-term hydrologic impact of urban sprawl. The L-THIA/NPS GIS model is a powerful tool for identifying environmentally sensitive areas in terms of NPS pollution potential and for evaluating alternative land use scenarios to enhance NPS pollution management. Access to the model via the WWW enhances the usability and effectiveness of the technique significantly. Recommendations can be made to community decision makers, based on this analysis, concerning how development can be controlled within the watershed to minimize the long-term impacts of increased stormwater runoff and NPS pollution for better management of water resources.