Bathymetry Data for Portions of Lower Granite Reservoir and Vicinity, Washington and Idaho, 2009-10

During autumn 2009 and winter 2010, the U.S. Geological Survey (USGS), in cooperation with the
U.S. Army Corps of Engineers (USACE), conducted a hydrographic survey using a multibeam
echosounder system (MBES). The survey was from river mile (RM) 130 to 142 on the Snake River,
and from RM 0 to 2 on the Clearwater River areas of Lower Granite Reservoir. The survey mapped
the part of the river that was accessible to the boat and the echosounder equipment, but very
shallow areas along the banks that were inaccessible or too shallow to be measured with
echosounder equipment were not mapped. The survey was conducted in 1-mile segments,
and the data were combined to provide a continuous digital elevation dataset of the reservoir
within the limitations of the project. The elevation points in the dataset were referenced to the
USACE established benchmarks using the real-time kinematic-global positioning system
(RTK-GPS); therefore, point elevations were unaffected by reservoir stage changes.