USING GIS-BASED GEOMORPHOLOGICAL STUDIES TO IMPROVE WATERSHED MANAGEMENT DECISION MAKING

Integration of geomorphological mapping of streambank and channel bottom features into a GIS database provides a valuable tool for watershed managers charged with balancing habitat protection and flood control issues. Maps of streambank stability, channel bottom morphology, riparian buffer width, woody debris, and barriers to fish movement were made on orthophotoquadrangles while walking or canoeing the entire length of the Poultney and Mettawee Rivers in Vermont and New York. The hand-drawn maps were later digitized into ArcView GIS using the orthophotoquadrangles as a common base. Once in a GIS format, statistical information on stream parameters can be easily compiled and relationships between features observed. For example, 48 percent of the eroding banks in the Poultney River watershed occur along the Hubbardton River tributary, which comprises only 23 percent of the river’s length. This high rate of erosion is strongly correlated with the presence of clay soils and the absence of a riparian buffer.

The GIS-based geomorphological maps are useful to watershed managers in several ways:

1. Provides the length of certain features along the river (e.g., the total length of stream needing riparian buffer improvement or the location of the longest reach on the river without a riparian buffer); 2. Permits the rapid analysis of relationships between different parameters at the watershed level and is not restricted to isolated reaches (e.g., the location of eroding banks relative to a particular soil type); 3. Defines the reaches of river along which certain habitat features might be found (e.g., a map of channel bottom morphology provides clues to where pool-riffle habitat for trout is located); 4. Assists in the prioritization of stream restoration sites by recognizing in advance the potential impacts of restoration activities in a given area (e.g., will streambank stabilization in one area cause erosion of banks downstream where the GIS data indicate no riparian buffer exists?); and 5. Provides simplified and rapid viewing of multiple parameters at a variety of scales (e.g., can first identify at the watershed scale an area with significant barriers to fish movement downstream of certain habitat features such as woody debris before zooming into those areas to determine the exact location to plan a site visit).