EPA Data - Background

With watershed and water quality-based assessment in mind, the EPA recently developed the Better Assessment Science Integrating Point and Nonpoint Sources (BASINS) software program. BASINS is an extension that runs within the ArcView platform. The BASINS program resulted in the development of this software as well as pre-packaged data for hydrologic modeling that includes the aforementioned USGS DEM data. The data developed by the BASINS program is a valuable resource in and of itself and can be independently applied to hydrologic modeling. The EPA has gone to great lengths to process NRCS STATSGO, USGS DEM and USGS Landuse/Landcover data into shapefile format. The data is packaged into predefined watershed boundaries each with their own USGS HUC (Hydrologic Unit Catalog) number. Predefined watersheds can be seen as both an advantage and disadvantage. If the region of study is smaller or larger than the predefined watersheds the GeoProcessing Wizard in ArcView can be employed to clip out the desired regionListed below are the advantages and disadvantages to using the EPA GIS data.

Advantages

• DEM, landuse and soil type data are all found at this site and are in easy to use .shp (shapfile) format.
• The DEM data is already separated into pre-defined watersheds for all fifty states as well as Puerto Rico.
• Easy to use GUI for selecting region of analysis.

Disadvantages

• The DEM data is in shapefile format (disadvantage for WMS, advantage for ArcView).  WMS can read 1:250,000 DEM data from the USGS site directly  The EPA data requires additonal steps to get the DEM data in a format useable in WMS.
• There's a lot of useless information included in the EPA Basin's "core.exe" data.
• The data is easier to use if the Basins software is downloaded and used to extract data and look at.
• A major downfall of using the EPA Basin DEM data is that it's in .shp file format and might require the use of the Spatial Analyst Extension in ArcView (or Arc/Info using the SHAPEARC command) to convert it from a shapefile to a grid and then export it as an ascii file.
• Varying sections of each HUC do not have data associated with that region (see below)

EPA shapefile with xyz data (i.e., DEM) - represents a specific Hydrologic Unit Code (predefined watershed)