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Corps Performs Lakebed Imaging Study for Erosion Analysis

Last year, the U.S. Army Corps of Engineers Detroit District began a lakebed imaging study to determine changes near the New Buffalo, Michigan, area. The Detroit District Hydrology and Hydraulics Office is analyzing the data to under-stand how the sand is moving and why, and what might be done to alleviate problems with erosion. In September 2015, 11 scientists and engineers spent two weeks collecting data to quantify the changes in the amount of sand in the coastal zone.

The majority of the work was done in-water, with some inland measurements and borings. The crew used a side scan sonar to detail the surface, and a sub-bottom profiler acoustic device penetrated about 50 feet. “Most of the sand is mobile in the top few meters of the lake. That’s the im-portant part,” Jim Selegean, hydraulic engineer, Corps Great Lakes Hydrology and Hydraulics Office, said. Data was collected for nine days with two research vessels, one towing a boat with the sub-bottom profiler, and one survey vessel.

The data collected will consist of bathymetry, side scan sonar, sub-bottom profiling, surficial grab samples, hand cores and underwater vid-eo. The analysis will use similar historical data from the U.S. Geological Survey (USGS) to measure erosion rates in the coastal zone over the last 30 years.

Selegean said when the harbor was built in the 1970s, the project included a large beach-fill to mitigate any sand that the harbor would block. Once that eroded away, the downdrift shorelines were back to their natural erosion rates. Also, shoreline development has increased the construction of dams and coastal shore pro-tection structures, which has further decrease the supply of sand to the coastal zone. “This study will quantify the response to this reduction in supply,” Selegean said.

The final results, which Selegean expects later this year, will help guide future coastal zone management decisions. 

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