Quantifying Channel Maintenance Instream Flows: An Approach for Gravel-Bed Streams in the Western United States

Abstract

This paper discusses one approach for quantifying channel maintenance instream flow necessary to achieve the Forest Service Organic Act purpose of securing favorable conditions of water flows. The approach is appropriate for quantifying channel maintenance flows on perennial, unregulated, snowmelt-dominated, gravel-bed streams with alluvial reaches. The approach identifies the minimum essential regime of streamflows necessary for the channel and its floodplain to remain fully functioning with respect to sediment and flow conveyance. The paper discusses the role of water, sediment, and vegetation in maintaining a channel and provides methodologies for estimating the upper and lower limits of the required sediment transporting flows. Conceptually, these flows range from intermediate flows associated with initial coarse sediment movement from the coarse surface layer of gravel-bed streams (Phase 2 transport) up to the 25-year flow event. The paper also provides suggestions for analyzing and displaying results, implementing studies at the watershed scale, determining data needs, and post-project management and evaluation. Best application of the approach occurs at sites having long-term bedload data and streamflow records.Publications Web Site:https://www.fs.usda.gov/rm/pubs/rmrs_gtr128.html

Citation

Schmidt, Larry J.; Potyondy, John P. 2004. Quantifying Channel Maintenance Instream Flows: An Approach for Gravel-Bed Streams in the Western United States. Gen. Tech. Rep. RMRS-GTR-128. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station. 33 p.