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GEOMORPHIC THRESHOLDS AND CHANNEL MORPHOLOGY IN LARGE RIVERS
Citation:
Kelly, V. J., D H. Landers, S. M. Jett, AND P R. Kaufmann. GEOMORPHIC THRESHOLDS AND CHANNEL MORPHOLOGY IN LARGE RIVERS. Presented at NISORS (Ninth International Conference on River Research and Applications), Albury, New South Wales, Australia, July 6-11, 2003.
Description:
Systematic changes in channel morphology occur as channel gradient, streamflow, and sediment character change and interact. Geomorphic thresholds of various kinds are useful metrics to define these changes along the river network, as they are based on in-channel processes that determine morphology and the associated habitat types. Energy-based indices can also be used to describe the river response to land-use activities and streamflow alteration, especially those that result in excess input of fine sediments. This is particularly relevant for habitat conditions in larger rivers, which are especially vulnerable because of their downstream location in the drainage network. We evaluate the use of geomorphic thresholds to describe channel morphology and habitat types in large (i.e. non-wadeable) rivers. Data was provided from the USEPA's Environmental Monitoring and Assessment Program (EMAP), a probability based survey that is developing approaches to characterize habitat and biological status of rivers in 12 western states. Additional data were derived from 1:12,000 color infrared aerial photos, which were converted to digital orthophotos. The digital images were classified for habitat elements, with a pixel size of 0.04 m2; minimum mapping units are 6.0 m2 for planform channel morphology and 500.0 m2 for terrestrial landcover. Preliminary classification of river channel and landscape types was done using simple geomorphic indices based on sediment transport competence, substrate size, and bed stability. We compared these results with data from field sampling and aerial photos to test the utility of geomorphic threshold indices to provide accurate prediction of channel form.