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

Multiplication by the number of seconds in a day converts fe Is-days to water volume in cubic
feet. Flood frequencies and the magnitude of floods of specific recurrence intervals were
calculated for several time intervals by fitting the plotting positions of annual maximum daily
peaks to a log Pearson Type III distribution. Maximum daily peaks were chosen for this
analysis, because instantaneous peak data cannot be computed for the synthetic portion of the
record prior to 1943. Average hydrographs for specific time intervals consist of the average of
all daily mean discharge records within the interval for each day of the water year. All records
for February 29 were removed from the time series before construction of average hydrographs.

Suspended-Sediment Transport

The USGS measured suspended-sediment concentrations in the Duchesne River at the
gaging station near Randlett on an approximately montWy basis between July 1975 and March
1989. We analyzed these 136 concentration measurements to produce sediment-rating relations
for estimating suspended-sediment discharge in the Duchesne River. Measurements were sorted
into high flow and base flow classes. Base-flow measurements for this analysis were defmed as
all concentration measurements taken at times when discharge was less than 600 fe/so
Measurements below this threshold exhibit no discernable relationship between concentration
and discharge (Figure 5). Discharge events greater than 600 fe Is generally occurred during the
snowmelt runoff season, and were separated into rising and falling limb flows according to
whether they occurred before or after that year's peak: date. Discharges greater than 600 ft3 Is
were recorded during fall and winter months on four occasions and were excluded from
subsequent high- flow analysis. Suspended-sediment measurements taken on the rising limb and
falling limbs of the annual spring peak showed distinct relationships between concentration and
discharge (Figure 5). Ratings relations were developed as follows:

C=C _ Cmx-Cmn
mx 1 + exp [k s (Q - Q *) ]

(1)

where Q is discharge in cubic meters per second, Cmx is a maximum concentration occurring at
large discharge, Cmn is the average concentration at base discharge, ks scales the discharge range
over which the transition from Cmn to Cmx occurs, and Q* is the midpoint of that range in cubic
meters per second. Equations of this form were fit by eye to base-flow plus rising limb data and

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