Geophysical, Sedimentological, and Photographic Data from the John Day Reservoir, Washington and Oregon

Recently, concerns about declining stocks of endangered anadromous salmonids in
the Columbia River basin raised the issue of restoration of riverine functions
in this and other Columbia and Snake River reservoirs (ISG, 2000; Dauble and
others, 2003). One option for restoration of riverine functions includes
lowering water levels within selected reservoirs such as the John Day
Reservoir. Questions about how much sediment has been trapped by this dam
warranted a detailed study of the floor of the reservoir to assess changes that
had occurred since impoundment. High-resolution geophysical mapping techniques
were employed to provide, to our knowledge, the first detailed view of the
floor of the reservoir since its formation. This geophysical "road map" in
concert with bottom video images, some sediment samples, and historical data
collected prior to creation of the reservoir were incorporated into a GIS. The
subsequent text summarizes the techniques used in this study. It also provides
a preliminary analysis of the results and a background for the GIS that
accompanies this report.

[Summary provided by the USGS.]