Surficial Geology and Analysis of Post-Impoundment Sediment of Lake Mohave; Interpretation of Sidescan Sonar and Seismic-Reflection Data

Lake Mohave is one of several multi-purpose reservoirs that have been
constructed on the Colorado River. The lake was formed upon completion of the
Davis Dam in 1953. Since then, research on this reservoir has dealt primarily
with vegetation surrounding the lake (Tallent-Halsell and Walker, 2002), fish
(Bozek and others, 1990), water quality (Paulson and Baker, 1983), and
geological hazards to recreation areas surrounding the lake associated with
flash floods (Glancy and Harmsen, 1975; Moosburner, 1979; 1981). Because no
lake-floor mapping had been conducted since completion of the Davis Dam, the
U.S. Geological Survey, in cooperation with researchers from the University of
Nevada Las Vegas, completed a geophysical survey of this lake in April 2002.
The survey included collection of sidescan sonar imagery of nearly the entire
lake floor, and of high-resolution seismic-reflection profiles along widely
spaced lines throughout the lake. These acoustic data were used to produce
detailed maps of the lake floor, which were subsequently used to determine the
amount of sediment that had accumulated in the lake since impoundment, its
distribution, and the processes of deposition. Information on sedimentation in
the reservoir is needed for several reasons:

(1) sediment diminishes the holding capacity and thus the longevity of the
reservoir,

(2) sediment can harbor pollutants that may have entered the lake, and

(3) the distribution and types of sediment shed light on the processes of
sediment dispersal through the lake.

The survey area extended from Willow Beach nearly to the Davis Dam (fig. 1).
The area north of Willow Beach could not be surveyed because it was too narrow
and shallow for the survey vessel.

[Summary provided by the USGS.]