GIS implications for hydrologic modelling: simulation of non-point pollution generated as a consequence of watershed development scenarios

Two different land development scenarios and separate trials for each were compared in terms of the nonpoint pollution (NPP) generated as a consequence of the location and condition of urban land within a drainage basin in central North Carolina, USA. The ANSWERS NPP model was used to estimate erosion, deposition, and related hydrologic parameters at the basin outlet occurring at individual 0.1 ha cells throughout the basin. The NPP model was interfaced to a vector (ARC/INFO) and a raster (ERDAS) GIS to generate and spatially organize the data to support each of the scenarios. The interface between the GIS and the hydrological model was established through the development of the ERDANS program. ERDANS, written in Fortran, provided a mechanism to link the power and flexibility of spatial data organized within a GIS environment with a distributed NPP model for the simulation and testing of environmental consequences of watershed development analyzed from a spatial perspective. Differences were observed in the amount of NPP at the basin outlet due to locational decisions in land development. Identical developments, occurring on the same set of biophysical variables and located within the upper, middle, and lower portions of the watershed, were evaluated through the combined power and flexibility of the ANSWERS/GIS approach. The effect of management strategies on the alleviation of NPP levels as a by-product of development was evaluated through the simulation of forested buffers around urban developments. The primary objective of the research was to explore the capability for GIS simulation of realistic watershed development scenarios, organization of disparate information within a spatial domain to support the simulation studies, and the linkage of a hydrologic model to the GIS for the evaluation of scenario impacts on the hydrologic system.