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Bathymetric and velocimetric surveys at highway bridges crossing the Missouri River between Kansas City and St. Louis, Missouri, May 22–31, 2017

April 14, 2020

Bathymetric and velocimetric data were collected by the U.S. Geological Survey, in cooperation with the Missouri Department of Transportation, near 10 bridges at 9 highway crossings of the Missouri River between Kansas City and St. Louis, Missouri, from May 22 to 31, 2017. A multibeam echosounder mapping system was used to obtain channel-bed elevations for river reaches ranging from 1,550 to 1,840 feet longitudinally and generally extending laterally across the active channel from bank to bank during moderate flood flow conditions. These surveys indicate the channel conditions at the time of the surveys and provide characteristics of scour holes that may be useful in the development of predictive guidelines or equations for scour holes. These data also may be useful to the Missouri Department of Transportation as a low to moderate flood flow comparison to help assess the bridges for stability and integrity issues with respect to bridge scour during floods.

Bathymetric data were collected around every pier that was in water, except those at the edge of water, and scour holes were observed at most surveyed piers. Occasionally, the scour hole near a pier was difficult to discern from nearby bed features. The observed scour holes at the surveyed bridges were generally examined with respect to shape and depth.

Although exposure of parts of substructural support elements was observed at several piers, at most sites the exposure likely can be considered minimal compared to the overall substructure that remains buried in bed material at these piers. The notable exceptions are piers 4 and 5 at structure K0999 on Missouri State Highway 41 at Miami, Mo.; piers 2 and 3 at structure G0069 on Missouri State Highway 240 at Glasgow, Mo.; and pier 5 at structure A4574 on Missouri State Highway 5 at Boonville, Mo. At these structures, the bed-material thickness between the bottom of the scour hole and bedrock was less than 6 feet.

Pier size, nose shape, and alignment to flow had a profound effect on the size of the scour hole observed for a given pier. Narrow piers having round or sharp noses that were aligned with flow often had scour holes that were difficult to discern from nearby bed features, whereas piers having wide or blunt noses resulted in larger, deeper scour holes. Several structures had piers that were skewed to primary approach flow, and scour holes near these piers generally indicated deposition on the leeward side of the pier and greater depth on the side of the pier with impinging flow. A riprap blanket constructed in 2015 around pier 4 of structures L0550 and A4497 on U.S. Highway 54 at Jefferson City, Mo., effectively mitigates the scour observed near those piers in previous surveys.

Previous bathymetric surveys exist for all the sites examined in this study. Bathymetric surfaces from a nonflood survey in 2013 and a flood survey in July 2011 at most of the sites are compared to the 2017 survey surfaces. The average channel-bed elevation at structure A4574 was remarkably similar in all three surveys and higher than what might be implied by a trendline along the reach between Kansas City and St. Louis, which may indicate this site is at or near a local feature that controls sediment deposition and scour.