Hydroacoustic Assessment of Construction-Related Activities for the Gilmerton Bridge Improvement Project

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) is required to address potential noise impacts 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 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 has an expected completion date in 2014.

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 to the sturgeon population would be exceeded.

HMMH recommended Best Management Practices include 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.

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