9493

• UCREFRP Catalog Number: 9493
• Author: Gaeuman, D., P. R. Wilcock and J. C. Schmidt.
• Title: High Flow Requirements for Channel and Habitat Maintenance of the Lower Duchesne River between Randlett and Ouray, Utah.
• USFW Year: 2003.
• USFW - Doc Type: \
• Copyright Material: NO

FINAL REPORT, November 2003
High-flow Requirements for the Duchesne River

base-flow plus falling limb data to yield the following suspended sediment concentration ratings
relations (Figure 5):

C = 2800 - 2680 ; rising limb (Ia)
1+ exp[0.08(Q- 55)]

C = 800 - 680 ; falling limb (1 b)
1+ exp[0.07(Q - 65)]

where discharge is in cubic meters per second and concentration is expressed in milligrams per
liter.

This functional form reflects reasonable constraints that are consistent with these data and
with better-measured concentration time series on comparable streams. Among the simplest, and
perhaps most common, functional form used for suspended sediment rating relations is the power
function. In this data set, suspended sediment concentration increases with discharge in a
manner that can be well represented by a power function only through only a small range of
flows that occur in the Duchesne River. These data show that no systematic correlation between
concentration and discharge is apparent under base flow conditions, such that base flow
concentrations are best represented by a mean value. Only two measurements are available to
represent concentrations at discharges approaching or exceeding bankfull flow. However, these
measurements indicate that there is an upper limit to the suspended sediment concentration.
Simply extrapolating a power function to higher flows would not capture this phenomenon.
Instead, extrapolation would produce extremely high concentrations that are inconsistent with
this data and with observations elsewhere. These constraints -low-flow concentrations that are
insensitive to discharge and an upper bound on concentration - define the relations we fitted to
the data.

Total annual suspended-sediment discharge was estimated for time periods before 1925
and after 1943, and for upper-quartile, lower-quartile, and middle-quartile years within the
period of measurement from 1943 to 2000. Upper-quartile years were defined as years with total
annual discharge in the upper quartile of all years in the measurement period Water years with
total annual discharge in the lowest quartile of all years in the measurement period were defined

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