An interactive GIS Watershed Assessment Model (WAM), which has been applied to over 30,000 km2 of northern Florida and New Zealand in the 1990s, was adopted for the ArcView platform in 2000 making it more user-friendly and accessible to engineers and planners. The model simulates
spatial water quality loads based on land use and soils and then routes and attenuates these source cell loads through uplands, wetlands and streams to watershed outlets. The model is almost entirely GRID based providing a higher resolution of results than models that rely on polygon coverages.
This version of the model includes a menu interface written in ArcView Avenue with the Spatial Analyst extension to let the user create modified land use scenarios and compare the results side-by-side with the results of the existing land use. Two innovations have been recently added to
the model to increase its utility and availability. Because of the programming complexity, the model could previously only be customized for a specific watershed by the original developers. The model has since been designed to allow water resource engineers and planners, with limited GIS experience,
to set up and customize the interface for their particular region. Algorithms originally in ARC/INFO AML format have been converted to ArcView Avenue scripts and step-by-step procedures have been established to guide the user through the model development process. Training has also been
made available. The second change includes the addition of point sources to the model. Known point sources of discharge can be added at any location within the watershed to simulate wastewater treatment plants or industrial dry weather contributions. In addition, wastewater treatment plant
service areas can be added to signal the model that certain processes are occurring so that the model can make appropriate adjustments. These new features strengthen the urban component of the model, which is already recognized for its agricultural and rural applications.
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