A private client enlisted Coastal Sensing & Survey to conduct a detailed search and imaging operation beneath the 520 Floating Bridge in Lake Washington, Seattle. The area, secured by cables attached to large concrete anchors 300 meters north and south of the bridge, had never been previously imaged and was notorious for being filled with debris, cables, and entangled poly rope. The mission presented significant challenges, requiring advanced imaging and navigation techniques to ensure safe, accurate, and comprehensive coverage.

Using a multi-sensor approach we were able to gain a clear picture of the cable structure and layout, map the shoreline topography, and identify any potential hazards in and around the cabling, both at the lake bed and in water column. Then ROV operations were undertaken, under and around the hazards using FLS sonar for both navigation and imaging.

Work in complex, high-risk environments like this demands more than basic coverage. Clear imaging and accurate positioning help reduce uncertainty, identify hazards, and support informed decision-making in survey areas where visibility is limited and margin for error is small. By documenting conditions beneath the bridge, this effort provided a record of a previously uncharted area.

What capabilities we used: Forward looking sonar (FLS), Sidescan, ROVs, Multibeam Bathymetry, Backscatter & ARA, Precision Positioning, Photogrammetry, and Subbottom.