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

as lower-quartile years, while water years with total annual discharge in the middle two quartiles
were defined as middle-quartile years. Average annual suspended sediment fluxes were
estimated by separating the records from each water year into rising and falling limbs of the
annual spring peak, multiplying each daily discharge by the daily load computed from the
appropriate ratings relation, and dividing by the number of water years in each interval or
quartile subset.

Geomorphic Mapping
The distribution of geomorphic surfaces in the alluvial valley of the Duchesne River
between Ouray and Randlett was mapped in the field in June 2000 onto a 1997 aerial photograph
base. The river configuration depicted on the 1997 photo base was generally consistent with
observed field conditions, except in a short reach known as the Bowtie (Figure 2) where there
were significant channel changes in 1998 and 1999. Major types of geomorphic surfaces defined
for this study include channel, bar surfaces, floodplain surfaces, and terrace surfaces. Each of
these major categories was further subdivided into several sub-types (Table 1). Mapping units
were distinguished in the field and on the photo base by elevation above the stream, surface
topography, vegetation, and surficial geologic materials. Unit boundaries were precisely drawn
on mylar overlain on the photo base in the field and subsequently adjusted in the laboratory with
the aid of stereoscopic viewing and standard photogeologic techniques. Map units and
geomorphic photo interpretations developed in the field and with the 1997 photographs were
applied to seven additional sets of aerial photographs taken between 1936 and 1993. Mapping
unit boundaries were drawn on mylar overlays for each photo set while viewing the photos
through a stereoscope. Because the degree of uncertainty in classification of surface units
increases on older or poor-quality photo bases, a system of inheriting map units from younger
photo bases was implemented. Once a map unit classification was determined for a map unit
observed on a given photo series, the same classification was assumed for the same surface on
the preceding photo series, unless there was compelling evidence of change. This method allows
surface classifications verified by field observation to be propagated to older photomaps for
which field verification is impossible. In applying this method, we recognize that the character
of some geomorphic surfaces change over time even in the absence of fluvial reworking. For

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