Introduction Alteration of stream flow regime and sediment loading from water development activities can result in both short- and long-term changes in channel morphology and conveyance capacity. Subsequently, the condition of the aquatic habitat can be affected. In recent years, much research and development effort has been directed toward the determination of suitable instream flows to maintain fisheries habitat in regulated streams (Stalnaker & Arnette 1976; Wesche & Rechard 1980). However, there are several facets of the instream flow problem which have not been adequately investigated, one involving the recommendation of flushing flows to simulate the peak runoff hydrograph characteristics of most unregulated streams (Reiser et al. 1985).
Limited research has been conducted to develop methodology for determining the magnitude, timing, and duration of flushing flows needed to maintain channel integrity and associated habitat characteristics through the movement of sediment deposits. Of the 15 methodologies identified by Reiser et al. (1985), a majority were not designed specifically to assess flushing flows, but rather were approaches for studying sediment transport problems. The several formal methodologies currently available (Wesche et al. 1977; Environmental Research & Technology, Inc. 1980; Rosgen 1982) were developed In response to immediate management needs and are relatively untested in terms of accuracy and reliability.
During 1984, the Wyoming Water Research Center initiated a research project entitled, "Development of methodology to determine flushing flow requirements for channel maintenance purposes." Objectives of this project are to 1) document the rate of change of various channel characteristics resulting from aggradation/degradation processes under altered flow regimes; 2) quantify the physical and hydraulic properties needed to transport deposited sediment through natural channels; 3) test the predictive capabilities of existing sediment transport models against field data; and 4) develop methodology to predict conditions of flow needed to flush sediments to maintain given streams In prescribed hydraulic, physical and biologic conditions.
One stream selected for study in response to these objectives was the North Fork of the Little Snake River (North Fork), a steep, rough, regulated, headwater stream. Wesche et al. (1977) recommended both maintenance and flushing flow regimes for the North Fork in light of the proposed expansion of water diversion facilities in the drainage by the City of Cheyenne, Wyoming, as part of their Stage II water development program. Construction of Stage II began in 1983. During the late summer of 1984, intense rainfall in the construction area resulted in the deposition of a broad size range of sediments in that section of the North Fork where flushing recommendations had been made. At the request of the Wyoming Game and Fish Department and in cooperation with the United States Department Agriculture Forest Service, the authors initiated a study of the North Fork. The objectives of this paper are to 1) describe the methods used to assess the extent of the 1984 sediment deposits; 2) present preliminary results summarizing the response of the deposited sediment to the 1985 spring runoff flow regime; and 3) evaluate the effectiveness of the 1977 flushing flow recommendations in relation to the 1984 sediment deposits.
Water Resources Publications List
Water Resources Data System Library | Water Resources Data System Homepage