7832

• UCREFRP Catalog Number: 7832
• Author: U.S. Bureau of Reclamation.
• Title: A Pilot For Long-Term Monitoring Of Resources On The Colorado River In The Grand Canyon Using Geographic Information Systems.
• USFW Year: 1995.
• USFW - Doc Type: \
• Copyright Material: NO

REPORT NO.4
DEVELOPMENT OF CHANNEL-GEOMETRY INFORMATION
FOR FLOW AND SEDIMENT-TRANSPORT MODELS
Julia B. Graf, Samuel M.D. Jansen,
J. Dungan Smith, and Stephen M. Wiele
U.S. Geological Survey
375 South Euclid Avenue
Tucson AZ, 85719-6644
Introduction
As a part of the GCES (Glen Canyon Environmental Studies), the USGS (U.S. Geological
Survey) began in 1991 to develop a suite of flow, sediment-transport, and bed-evolution models
for prediction of sand accumulation or loss in various reaches of the Colorado River and for
determination of the response of sand deposits to discharges in the river produced by dam
releases. Accurate characterization of channel geometry up to the highest elevation affected by
all proposed or possible flows is required for these single and multidimensional models.
Topographic information from published USGS topographic maps is not precise enough for use
in the flow and sediment transport models under development and does not give channel
morphology below the water surface.
The USGS began collecting bathymetric data for the river reaches in Reclamation's (Bureau of
Reclamation) GIS data base in 1991 to supplement the topographic information in that archive
that was developed photogrammetrically with bathymetry and to define the bed morphology for
model development.
Reach 5 of the GCESIGIS set, extending from river mile 60 to river mile 72, was selected as the
reach in which to begin model development because the Little Colorado River, which joins the
Colorado River at river mile 61, is the largest source of sand for the Colorado River in Grand
Canyon National Park, and because the reach downstream from the Little Colorado River mouth
is important to native fish. Maps showing the combined Reclamation topographic and USGS
bathymetric data are being prepared for the reach from just below the Little Colorado River
confluence to just above Tanner Canyon Rapid at river mile 68.5-a 10.3-km segment of the
19-km4ong GCES/GIS reach. The maps (fig. 14) will show topography with a contour interval
of 1 m, except where near-vertical slopes make contours at that interval unreadable.
Methodology
Bathymetric data were collected with two generations of manual-tracking, range-azimuth
positioning systems. Both systems consist of an electronic theodolite to establish the ties to the
control network and a modified laser EDM (electronic distance meter)-mounted above the
theodolite-to track a boat-mounted target. Depth was measured with a sonic depth sounder,
then digital position and depth data were sent directly or via radio modems to a datalogger or
laptop computer. Depth also was recorded on paper charts.
Position information is lost or incorrect information is recorded when an instrument operator
fails to track the boat within a preset tolerance, when the operator loses sight of the boat as it
passes behind a rock outcrop, or when the laser reflects off an object other than the target, such
as a tree or a cliff face beyond the boat. Also, interference can occasionally cause the radio
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