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Project Experience: Hydroacoustic Assessments for Gilmerton Bridge Improvements, Virginia

The Challenge

In 2012, two distinct population segments of the Atlantic sturgeon (Acipenser oxyrinchus oxyrinchus) were listed as endangered by the National Marine Fisheries Service (NMFS), National Oceanic and Atmospheric Administration (NOAA), under the Endangered Species Act (ESA) of 1973, as amended. As a result of this action, the Virginia Department of Transportation (VDOT) found that it had to address potential noise impacts to the species due to construction-related activities associated with construction of a fender system for the new bridge, the dredging of the navigational channel, and the removal of cofferdams and timber piles during the demolition of the old bascule bridge.

The Strategy

HMMH performed a hydroacoustic assessment of pile driving activities to estimate the geographic range within the river, at which the estimated thresholds for the onset of behavioral effects and physical harm would be exceeded.

The Solution
Recommended Best Management Practices (BMP) included the use of an air bubble curtain system for pile driving activities during the installation of the fender system and a confined bubble curtain system for the extraction of sheet steel piles using a vibratory hammer.

The Gilmerton Bridge Improvement Project provided a new lift span bridge over the Southern Branch of the Elizabeth River, replacing the double-leaf bascule bridge that was constructed in 1938. The reconstructed four-lane Gilmerton Bridge was opened for traffic in late 2013 and is expected to be completed in 2015.