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

example, we believe some areas classified as cottonwood terrace in 1997 were active floodplain
in 1936.

Creation and Analysis of GIS Databases
Geomorphic map overlays drawn on the aerial photographs were digitized into a
geographic information system (GIS) and assigned database attributes. These data were
examined to evaluate historical changes in channel form and size, and changes in the distribution
of other alluvial surfaces. Completed GIS coverages were developed from mapping using
photographs taken in 1936, 1948, 1961, 1969, 1980, 1987 and 1997. A coverage from photos
taken in 1993 showed no apparent change from the 1987 coverage in preliminary comparisons,
and so was not included in subsequent GIS development.

Digitizing:

Arc/Info@ GIS software and a Ca1comp 9100@ digitizing tablet were used for all
digitizing. Control points were identified for each photo base using a variety of quasi-stable
features such as road intersections and individual bushes or trees that could be located on USGS
orthophoto maps. Identification of adequate positional control for this study area proved
difficult, as cultural features are few and natural features change over time. Most roads available
for control in the area are dirt tracks that also may change in position over time. Nonetheless,
root mean square (RMS) errors were modest for most scenes digitized, averaging 6.5 m for the
1936, 1961, 1969, 1980, 1987 and 1997 coverages. Reported RMS errors were considerably
greater for the 1948 photos at 33.9 m (Table 2). These photos, believed to have been taken
during military training flights, are subject to significant distortion cause by aircraft tilt. The
errors associated with the finished GIS coverage were reduced from the reported RMS error by
an unknown amount by a rubber-sheeting procedure, described below, which was applied to the
digitized scenes.
During digitizing, the GIS software places the specified control points within the
coordinate system according to the given control point coordinates. Any positional error in
control point locations on the photographs will cause the actual control point locations in the
digitized coverage to be placed at slightly different coordinate locations than the coordinate
locations specified. The rubber-sheeting procedure used in this study consists of digitizing

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