South Dakota Watershed Boundary Dataset Completed

Executive Summary

In February 2008, the Watershed Boundary Dataset (WBD) for South Dakota received provisional Certification.  The WBD is a national digital dataset of nesting drainage basin boundaries delineated primarily from 1:24,000-scale source data.  The WBD in South Dakota was completed by the U.S. Geological Survey South Dakota Water Science Center in cooperation with the U.S. Department of Agriculture Natural Resources Conservation Service, the South Dakota Association of Conservation Districts, the U.S. Environmental Protection Agency, and East Dakota Water Development District.  The WBD is a refinement of the 8-digit hydrologic unit map, which in South Dakota was based on 1:250,000-scale source data.  The WBD redefined the 8-digit hydrologic unit boundaries and further subdivided the 8-digit hydrologic units into 10- and 12-digit hydrologic units.  The resulting Geographical Information System (GIS) data set provides a base layer of drainage boundaries and watershed information that may be used in a wide variety of applications by individuals and organizations involved in water-resources management activities.

Redefining watershed boundaries using 1:24,000-scale source data has produced boundaries noticeably different than the 1:250,000-scale boundaries in some areas (figure 1).  Additionally, drainage boundaries in other areas were revised based on field observations.  A series of wetter-than-normal years in the 1990s caused dramatic increases in lake levels in areas of northeast South Dakota. One such area was the North Big Sioux Coteau (previously identified as hydrologic unit 10160010), which had generally been considered "noncontributing" but was included in the James River drainage basin.  As the water levels of many lakes in this area rose and lakes began to coalesce, eventually these water bodies began to spill to adjacent waterways.  By noting the direction of flow at bridges and culverts, it was determined that portions of 10160010 did indeed drain to two separate 8-digit hydrologic units in the James River Basin, whereas other areas drained to the Big Sioux River Basin.  By definition a hydrologic unit in non-coastal areas can only have one outlet, so the area formerly occupied by 10160010 was split and merged into adjacent hydrologic units of the James and Big Sioux River Basins.  The next hydrologic unit in the James River Basin (10160011) was then re-coded to 10160010 to avoid skipping a code in the numbering sequence.  To a lesser degree, several additional hydrologic units had their boundaries similarly changed as shown in figure 1, although no other re-coding was necessary.

Instructions for Downloading the Watershed Boundary Data Set

The South Dakota WBD is currently available for download from the Natural Resources Conservation Service (NRCS) Geospatial Data Gateway (Gateway) at http://datagateway.nrcs.usda.gov/.  There is no cost to use the Gateway, but users must register before data downloads may be received.  To download the South Dakota WBD from the Gateway, click on Get Data on the main Gateway page.  On the resulting web page, drag a box to zoom in to your area of interest.  Further zooming or panning may be necessary for areas with a small extent.  Once you have identified your area of interest, click on Define Order Area and drag a box encompassing your area of interest.  The following screen will show a list of products available for your area of interest.  Place a check in the box near 12-Digit Watershed Boundary Dataset.  Additional products also may be checked if desired.  After you have finished selecting products to download, click on the Continue to Step 3 button.  Step 3 allows the user to select projection, extent, and file format options available for some products.  Click on the Continue to Step 4 button.  Step 4 allows the user to select a delivery method (choose FTP download) and provides the registration form.  If the Save Values box is checked, a user will only need to register once for a given computer.  Click on the Continue to Step 5 button.  After verifying that your information is correct, click on the Place Order button.  Depending on the size of your order, within several minutes you will receive an email with one or more download links (one for each product ordered).  The Watershed Boundary Dataset is distributed by 8-digit hydrologic units.  Note that depending on the location of your order and the extent options chosen, the zip file that you download may consist of more than one 8-digit unit.  After downloading, the file will need to be unzipped.  Metadata and other descriptive text is included with each Gateway download to document the products received.

The South Dakota Watershed Boundary Dataset will be updated periodically as more data becomes available.  If you find an error in a watershed boundary, please notify the South Dakota Watershed Boundary Dataset steward.

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