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Hydrographic Survey of Riverbed Erosion

Members of the US Geological Survey were filmed while out on the Missouri River at Williston, North Dakota, USA, performing a hydrographic survey to monitor the state of riverbed erosion. They were using a multibeam echo sounder which transmits sound energy and analyses the return signal (echo) that has bounced off the riverbed or other objects. Multibeam sonars emit sound waves from directly beneath a ship's hull to produce fan-shaped coverage of the riverbed. 

Gauge height at the Williston gauge was approximately 27.65 feet when this video was taken. Additional information about the USGS streamgauge at Williston is available at http://waterdata.usgs.gov/nd/nwis?program=nwisman&site_no=06330000