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-jlow Requirements for the Duchesne River

5. The increase the recurrence period for daily mean discharges of 4,000 fe/s or greater since
1971 has contributed to a consistent trend of channel narrowing since 1969.
6. Fine sediment accumulation related to a 50-percent reduction in stream flow after the 1920s
and an increase in the local sediment supply resulted in significant channel narrowing, the
loss of side channel habitat, and large-scale avulsions on the lower Duchesne River.
7. Modest flushing flows to prevent further accumulation of fine sediment in the lower
Duchesne River are proposed in addition to the channel-forming flow regime.
8. Existing measurements of suspended sediment concentrations in the lower Duchesne River
are inadequate for making well-constrained estimates of suspended sediment loads during
high discharge periods. An extended sampling program to monitor suspended sediment
concentrations in the lower Duchesne River during peak flow events should be undertaken.

Past and Present Characteristic of the Study Area
The channel of the lower Duchesne River has a meandering planform, and a mixed bed of
cobbles, gravel, and sand upstream from about river kIn 9. The river has historically been active
through much of this gravel-bed portion, and remains so to the present day. The character of the
Duchesne River changes abruptly downstream from river kIn 9. Channel gradient flattens, and
the channel assumes a deep, narrow geometry. Bed material changes from gravel to sand, and
the channel becomes fully sand-bedded by river kIn 7. The pool-riffle channel morphology with
wide point bars and a complex shoreline found in the upstream part of the study area is replaced
by a simple canal-like channel with steep, well-vegetated banks.
The 20th century geomorphic history of the lower Duchesne River includes complex
adjustments to changes in both sediment supply and water discharge. The nature of the
adjustments has varied both spatially and temporally over a period of at least 65 years, and
continues to influence river morphology to the present day. This history can be condensed into a
few periods of consistent trends and processes. These are 1) channel narrowing, filling of side
channels, and avulsions before 1950,2) channel metamorphosis involving extreme widening ofa
short reach downstream from the Pipeline between 1948 and 1987,3) bend extension with
frequent chute cutoffs throughout the middle part of the study area, and 4) relative stability in the
upstream part of the study area.

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