BKL was engaged by the Vancouver Convention Centre Expansion Project (VCCEP) to perform underwater measurements of pile driving noise to assess the impact on the nearby fish habitat. The purpose of our testing was to determine the zone where pile driving noise exceeded the Department of Fisheries and Oceans criterion of 30 kPa peak level.
Underwater noise from piles driven with a Berminghammer B-6505 HD diesel impact hammer were measured using a Bruel & Kjaer Type 8103 Hydrophone connected to a Type 2250 Frequency Analyser. Measurements were made at two depths at a large number of setback distances and for a large sample of piles being driven to establish the sound propagation over distance and over shallow/deep water and soft/hard ground.
A bubble curtain was being used to reduce sound propagation to the fish habitat. A bubble curtain was created using a circular tube with a large number of orifices placed on the sea bed around the pile to be driven. Compressed air flows out of the orifices to make a “curtain” of air around the pile. This provides a barrier to the sound coming off of the vibrating pile because the water-borne sound has to transfer its energy to the curtain of air and then back to the open water. We performed measurements with and without the bubble curtain in place and found that it reduced the zone of influence by a factor of four when properly deployed.
The results from our measurements were plotted and submitted for interpretation by the environmental consultant and in turn by the Department of Fisheries and Oceans.