Elevation and watershed boundary data can be obtained from multiple sources. In this example, we downloaded water boundary shapefile and elevation data in the form of Digital Elevation Model (DEM) raster from the United States Geological Survey’s (USGS) National Map Viewer. A DEM is a representation of the bare ground topography (elevations) excluding trees, buildings, and any other surface objects. We can pre-process the elevation data and input it into HEC-HMS to create a terrain dataset (see Preparing Terrain Data for HEC-HMS Using Q-GIS and Preparing Terrain Data for HEC-HMS using Arc-GIS tutorials), which can then be loaded into a Basin Model for hydrologic analysis (see Creating and Linking Terrain Data into a Basin Model). The watershed boundary is useful to clip the extent of the terrain raster for smaller file sizes and faster processing.
Step 1: Download terrain data
In the National Map Viewer, navigate to your location on the map.
- To download DEM data for the area of interest, select Elevation Products (3DEP) (1), the desired resolution (2) and geoTIFF file format in the left-side menu, as shown below.
- Click Search Products (3) to display the available datasets.
- Hover over the list of files on the left side or click on Footprint (1) to see the extent of each file.
- Select DEM(s) and click on Download Link (2, 3) to download the raster files in *.tif format.
- Two 1 Arc-second terrain datasets (n40w076 and n41w076) were downloaded to cover the extent of the watershed.
Step 2: Download watershed boundary dataset
Download the watershed boundary dataset for the area of interest.
- Select Watershed Boundary Dataset (1) under the Hydrography menu of the Datasets tab, as shown below.
- Check HU-2 Region (2) under Data Extent.
- Check Shapefile (3) under File Formats and click on Search Products (4).
- Click on the Products tab (1). The datasets span areas at HUC-2 level and contain watershed boundary shapefiles at all HUC levels. We will use HUC-10 level shapefile in this example.
- Click on Download Link (ZIP) (2) to download the shapefile.