Grand Canyon Riverbed Sediment Changes, Experimental Release of September 2000 - A Sample Data Set

An experimental water release from the Glen Canyon Dam into the Colorado River
above Grand Canyon was conducted in September 2000 by the U.S. Bureau of
Reclamation. The U.S. Geological Survey (USGS) conducted sidescan sonar surveys
between Glen Canyon Dam (mile -15) and Diamond Creek (mile 220), Arizona (mile
designations after Stevens, 1998) to determine the sediment characteristics of
the Colorado River bed before and after the release. The first survey
(R3-00-GC, 28 Aug to 5 Sep 2000) was conducted before the release when the
river was at its Low Summer Steady Flow (LSSF) of 8,000 cfs. The second survey
(R4-00-GC, 10 to 18 Sep 2000) was conducted immediately after the September
2000 experimental release when the average daily flow was as high as 30,800 cfs
as measured below Glen Canyon Dam (Figure 2). Riverbed sediment properties
interpreted from the sidescan sonar images include sediment type and sandwaves;
overall changes in these properties between the two surveys were calculated.

Sidescan sonar data from the USGS surveys were processed for segments of the
Colorado River from Glen Canyon Dam (mile -15) to Phantom Ranch (mile 87.7,
Figure 3). The surveys targeted pools between rapids that are part of the Grand
Canyon Monitoring and Research Center (GCMRC http://www.gcmrc.gov/) physical
sciences study.

Maps interpreted from the sidescan sonar images show the distribution of
sediment types (bedrock, boulders, pebbles or cobbles, and sand) and the extent
of sandwaves for each of the pre- and post-flow surveys. The changes between
the two surveys were calculated with spatial arithmetric and had properties of
fining, coarsening, erosion, deposition, and the appearance or disappearance of
sandwaves.

This report describes GIS spatial data files for this project and provides
examples of the data from the Colorado River near mile 2 below the confluence
of the Paria and Colorado Rivers. The complete data set includes sidescan sonar
images and interpreted map files for each of the pre- and post-flow surveys and
the changes between the segments of rivers.

[Summary provided by the USGS.]