Are High and Low Flow Habitat Values Really the Same?

by Terry Waddle, U.S. Fish and Wildl. Serv., Fort Collins, United States,

Document Type: Proceeding Paper

Part of: Water Resources Planning and Management: Saving a Threatened Resource—In Search of Solutions


The Instream Flow Incremental Methodology calculates physical habitat as a weighted sum. Suitability of use information for each modeled species and life stage are used to weight each area unit in a stream section and the weighted areas are summed to get a habitat index called Weighted Usable Area (WUA). Recent work in the Dolores River, Colorado shows the WUA for adult trout at high discharges to be less than at very low discharges. This may lead to the inference that a bank full discharge is a less survivable event than a very low flow. Biomass data do not support this conclusion. Possible causes of this phenomena include the streambed sampling method, hydraulic extrapolation error, and suitability of use data deficiencies. Some potential remedies are discussed and research needs are identified.

Subject Headings: Streamflow | Low flow | Rivers and streams | Water discharge | Mathematical models | Simulation models | River flow | Biomass | Colorado | United States

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