The concept of TMDL is based on Water Quality. By using a Watershed Action Plan, the TMDL initiative looks at water quality in a waterbody based on its watershed. One program utilized to assess the quality of a waterbody is BASINS 2.0, distributed by the Environmental Protection Agency. BASINS stands for Better Assessment Science Integrating Point and Nonpoint Sources.
The BASINS program presents a water quality assessment tool which uses GIS to examine environmental information, consider point and nonpoint pollution sources and manage this information in a watershed format. BASINS has five major components:
a national database comprised of spatially distributed data, environmental monitoring data, and point source data
assessment tools for analyzing water quality and pollution sources
utilities for importing case-specific data
watershed and water quality models
postprocessing tools for displaying results.
The nature of BASINS makes it seemingly ideal for use with the TMDL project. Because BASINS contains the Utility Tool Import, TMDL segments and their respective watersheds can be imported into the BASINS view, a view in an ArcView format, for further analysis using the water quality models it provides. For more information on the actual application of the models, see the term project paper by Jordan Furnans, Surface Water Quality Modeling for TMDL Development in Texas.
The watersheds delineated in my project procedure can be applied to water quality modeling by importing them, and the TMDL segments into BASINS. These steps will describe how to import the data.
First, the segments and watersheds must be in the same projection and datum, NAD83 as the BASINS project being used. Project both the segments and the watersheds in a separate ArcView project. Click on the Import button (Add Theme button in ArcView) and Select Data Type: BASINS Reach File, V3. Add the projected TMDL segments theme. A river network will appear on your basin. These are your TMDL segments.
Click on the Import button again, and Select Data Type: BASINS Watershed. Add the projected watersheds delineated for the TMDL segments. Click on No to projecting the data. This should have been previously performed. Select Reach File, Version 3 as the reach file, and the Reach File, V3 for the actual RF3 segments, not the TMDL segments, as the Reach File, V3 theme.
The TMDL Segments and respective watersheds have now been added to the BASINS View and can be used for analysis. In order to use the NPSM model with these delineated watersheds, you must trick the program. With the Projected Watersheds theme active, click on the W for Watershed Delineation. Select Reach File, V3 for the actual RF3 reaches as the Reach File, V3 theme and click OK. Then, click Cancel to Do you want to modify this watershed delineation?. Now, you can select a watershed, and run the NPSM model from the Model Menu. This model will assess water quality based on the delineated watersheds.
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