Characterization of Underwater Sounds Produced by Trailing Suction Hopper Dredges During Sand Mining and Pump-out Operations
ENGINEER RESEARCH AND DEVELOPMENT CENTER VICKSBURG MS ENVIRONMENTAL LAB
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Underwater sounds were characterized for three trailing suction hopper dredges TSHD during the removal of 3.1 million yd3 of sand from an offshore borrow area and during offloading of the escavated sediment at the pump-out stations in support of the Wallops Island, Virginia Beach Stabilization Project. Sounds were recorded simutaneoulsy at two depths, 3 and 9.1 m from the surface. Sound sources included sediment removal, pump-out of material, pump-out of clear water during pipe flushing, and transit to the borrow site hopper empty and to the pump-out stations fully loaded. Received and 13-octave Sound Pressure Levels dB re 1 Pa, rms are reported for each sound source. Source Levels dB re 1 Pa-1m, rms were back-caculated using fitted regression 15.788LogR. Source Levels SL ranged from 161.3 dB to 176.7 dB re 1 Pa-1m rms. Highest SL were obtained for the dredge Liberty, which is nearly twice the size e.g. hopper volume, displacement of the dredges Padre and Dodge Islands. Sounds emitted during transit produced the highest SL, whether the hopper was empty or full. Attenuation to ambient was dependent on the sound source, and ranged from 0.85 km flushing pipes to 2.65 km during transit with the hopper at maximum capacity.