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

where 5L1Si is the uncertainty in the change in storage in subreach i, 5 V. is the volumetric

uncertainty summed for all erosion polygons in subreach i, and 5 v.' is the volumetric uncertainty

summed for all deposition polygons in subreach i.
Equation 7 indicates that the magnitude of the uncertainty margins associated with
storage changes are based on the uncertainties associated with the total volume of erosion plus
deposition within a subreach, rather than on the net volume difference between erosion and
deposition (the storage change). Where the total volume of erosion plus deposition is large but
the magnitudes of erosion and deposition are similar, the net storage change is relatively small.
The uncertainty margins associated with these relatively small storage changes can be
comparatively large, and in some cases are much greater in magnitude than the storage changes
(Table 7).

Hydraulic Modeling
HEC-RAS software (US Army Corp of Engineers 1998) was used to model one-
dimensional steady flow at three detailed study sites and through an extended downstream reach
of the Duchesne River to its confluence with the Green River. Models at the three detailed study
sites were intended to evaluate the discharges necessary to inundate targeted geomorphic
surfaces and to initiate movement of the gravel substrate. A variable number of monumented
channel cross sections were surveyed and monitored through two runoff seasons to gather stage-
discharge data for use in model calibration. The modeling effort in the downstream portion of
the Duchesne River was intended to determine the extent to which backwater effects from the
Green River control stage, and therefore the extent of flooding, in the downstream portion of the
study area.

Data Acquisition

We established, developed, and monitored three detailed study reaches in the gravel-
bedded portion of the Duchesne River during the 2000 and 2001 field seasons. The locations of
these sites, 24-hour Camp, Above Pipeline, and Wissiup Return, are shown on Figure 2.
Although each site was visited for monitoring purposes on numerous occasions over the course
of two field seasons, relatively high flows useful for model calibration were rare during the study
period. Runoff during spring 2000 was exceptionally low, making collection of high-flow

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