Hydroacoustic measurements and modeling of pile driving operations in Ketchikan, Alaska

Abstract

Underwater acoustic measurements of pile driving operations were made at the Ketchikan ferry terminal in July 2016. At the time of the measurements, marine mammal injury and disturbance criteria developed by the National Marine Fisheries Service (NMFS) were based on sound pressure level (SPL) thresholds. Shortly after the measurements, NMFS changed the injury thresholds to a dual criteria involving peak pressure and sound exposure levels specific to marine mammal functional hearing groups. This paper presents distances to both injury criteria and the (unchanged) SPL-based disturbance criteria for vibratory driving and impact hammering 30-inch diameter cylindrical piles. Threshold distances were obtained using empirical regressions of sound levels measured by seabed-mounted recorders at 10 and 1000 m nominal range. A finite-difference method pile driving source model was used with a parabolic equation propagation model to compare measurements with simulations and to estimate received levels at all ensonifi...