Minnesota Lake Watershed Delineation (Lakeshed) Project
What is the Lakeshed Project?
The objectives for the project are:
Lakeshed data is available in:
- The Minnesota Geospatial Commons has various kinds of natural resource-related geographic and attribute data that may be downloaded by internet users.
- The lakeshed boundaries, as well as other watershed delineations, are included in the MNDNR Watershed Suite.
- There are 6 levels of watersheds available; make sure to read the metadata [HTML] to determine which ones you need.
- The lakeshed boundaries for lakes >= 100 acres are found in the MNDNR Level 08 - All Catchments layer within the suite.
- The Watershed Boundary Dataset (WBD) of the USGS and NRCS (Natural Resources Conservation Service) will contain watersheds for the entire country.
- The USGS offers StreamStats , a Web-based Geographic Information System (GIS) application designed to provide users with access to an assortment of analytical tools that are useful for water-resources planning and management.
Maps: A limited number of maps will be prepared; generally one for each major watershed and for high-interest lakes. These maps will be available for download from this web site, suitable for printing either on a desktop or commercial printer (e.g. at Kinko's).
How is the Lakeshed Project being completed?
The delineation of the Dent Lake watershed in Cook County is described below using elevation contour (DRG) and shaded relief (DEM) data in the background.
The boundary of a watershed is started at its outlet location, known as a pour point (yellow ring). This is usually chosen at the confluence of two or more streams or at the outlet of a lake as shown here. The boundary (red line) traces around the watershed following hilltops, ridgelines or other high points of elevation and finishes where it started: at the pour point. Ultimately, the boundary encompasses all of the land that drains into the given stream network or lake and out at its pour point.
Watershed delineation is currently done using GIS (Geographic Information System) software. This allows the user to display many different layers of data at once (e.g. streams, lakes, elevation)on the computer screen to use as locational reference for placing the pour points and watershed boundaries. The GIS software can also be used to process the watershed data for scientific studies or water resource management needs.
Some of the locational reference data used in delineating the watershed boundaries and pour points:
- DRG (Digital Raster Graphic): Scanned images of USGS topographic maps that contain elevation contours, water and land features. This is the primary locational reference data used in the Lakeshed Project.
- DOQ (Digital Orthophoto Quadrangle): Aerial black and white photographs of the earth's surface that have been geometrically corrected to eliminate distortion caused by camera tilt and terrain relief (i.e. so all features in the photos appear at right angles to the ground surface with minimum shadowing). This data is more recent than the DRGs and therefore may show changes to the landscape not visible on the DRGs.
- NWI (National Wetlands Inventory): Wetland areas delineated by the USFWS (U.S. Fish and Wildlife Service) through aerial photo interpretation and field verification. Watershed boundaries are delineated to avoid these areas if possible.
- PWI (Protected Waters Inventory): State-protected lakes delineated by the DNR using the National Wetlands Inventory (NWI) data, elevation data and aerial imagery. This data is used to help identify lake shorelines and place lake watershed boundaries and pour points.
- DEM (Digital Elevation Model): A digital grid of uniform square cells overlaying the earth's surface where each cell is assigned the elevation of the land (or water) surface it overlies. In combination with relief shading, the DEMs are color-coded according to their elevation value. The result is a 3-D-appearing background that helps elucidate the elevation contour data found on the DRGs. More information on DEMs and how the Lakeshed Project uses them.
Contacts for the Lakeshed Project
800 Oak Savanna Lane SW
Cambridge, MN 55008
DNR Waters, Box 32
500 Lafayette Road
St. Paul, MN 55155