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<br />.;/
<br />
<br />, overestimate the bedload equivalent part of total sediment discharge for some
<br />high-flow sediment discharge estimates. Subsequent annual sediment load
<br />computations and analyses utilized the sediment transport equations based on
<br />measured sediment discharges.
<br />
<br />Flood discharges greater than 12,000 ft3/s scour the riverbanks and the
<br />riverbed, and cumulatively transport roughly oneMfourth of the annual sediment
<br />load in the lower Yampa River (fig. 7). Reducing annual streamflow or alter-
<br />ing the time and range of discharge peaks can affect sediment transport to
<br />varying degrees. Altering the'duration of high and low discharges (fig. 8),
<br />while leaving mean annual volume of runoff unchanged can result in appreciable
<br />reductions in the mean annual sediment load. If the balance of sediment
<br />supply and transport is disrupted by a change either in local sediment transM
<br />port or sediment supplied from upstream, a period of instability characterized
<br />by channel aggradation or degradation may result.
<br />
<br />A sediment budget for the Yampa River at Deerlodge Park was developed
<br />using prevailing hydraulic conditions of slope, channel geometry, velocity
<br />distribution, stageMdischarge relation, sediment discharge-water discharge
<br />relation, and sediment size distribution. The sediment budget provides
<br />estimates of annual sediment surpluses or deficits, given several combinations
<br />of streamflow frequency distribution" annual streamflow, and annual sediment
<br />supply. As a management tool, the sediment budget cannot predict the specific
<br />geomorphic response of the river system to changes in hydrologic variables.
<br />It does provide information on combinations of mean annual streamflow and mean
<br />annual sediment supply, for specified flow-frequency distributions, that could
<br />maintain a balanced sediment budget, thereby minimizing accompanying channel
<br />adjustments. Scenarios presented in this sediment budget analysis are hypo-
<br />thetical and are presented as an example of how the analysis may be used.
<br />Other streamflow-frequency distributions, mean annual streamflows, or mean
<br />annual sediment supplies may be substituted in computations to estimate mean
<br />sediment surpluses or deficits.
<br />
<br />REFERENCES
<br />
<br />Andrews, E. D., 1978, Present and potential sediment yields in the Yampa River
<br />basin, Colorado and Wyoming: U.S. Geological Survey Water-Resources
<br />Investigations Report 78-105, 33 p.
<br />Carter, R. W., and Davidian, Jacob, 1968, General procedure for gaging
<br />streams: U. S. Geological Survey Techniques of Water-Resources Investi-
<br />gations, Book 3, Chapter A6, 13 p.
<br />Colby, B. R.. and Hembree, C. H., 1955, Computation of total sediment dis-
<br />charge, Niobrara River near Cody, Nebraska: U.S. Geological Survey
<br />Water-Supply Paper 1357, 187 p.
<br />Emmett, W, W., 1980, A field calibration of the sediment-trapping characteris-
<br />tics of the Helley-Smith bedload sampler: U.S. Geological Survey Profes-
<br />sional Paper 1139, 44 p.
<br />Guy, H. P., and Norman, V. W., 1970, Field methods for measurement or rluvial
<br />sediment: U,$, Geological $w'vey Techniques of Water-Resources Investi-
<br />gations, Book 3, Chaptel' C2, 59 p.
<br />
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