Lower Granite Reservoir Bathymetric and Underwater Video Surveys

Science Center Objects

Sedimentation of Lower Granite Reservoir, operated by the U.S. Army Corps of Engineers, affects commercial navigation and reservoir storage capacity. Some groups are concerned that dredging the reservoir to remove excess sediment may negatively affect endangered species such as steelhead and salmon.

During the fall of 2009 and the winter of 2010, our scientists mapped the bed of the reservoir using a multibeam echo sounder and an underwater video system to provide the U.S. Army Corps of Engineers with information about the bathymetry of the reservoir and the Snake and Clearwater Rivers upstream of the reservoir. We provided a digital elevation dataset of the area that the Corps can use to model sediment transport and deposition to the reservoir. We also developed a surficial sediment facies map to show what types of materials have been deposited in specific areas of the reservoir. The Corps will use the underwater videos and the facies map to evaluate benthic habitat conditions.

The bathymetric survey data revealed areas where sediment has formed underwater sand dunes. It also clearly shows basalt outcrops, scour holes, and areas where riverbed material was removed to provide material for levee construction. The underwater video survey, paired with the bathymetric survey, provided information about the benthic habitat of the reservoir in greater detail than ever before.