Ocean acoustic effects of explosions on land: Evaluation of Cook Inlet beluga whale habitability

Abstract

The Eagle River Flats is an impact region for artillery at Fort Richardson, Alaska. Adjacent to the Flats is the Knik Arm of Cook Inlet which is the habitat for a distinct population of beluga whales (Delphinapterus leucas). In order to assess the effects of 155 mm artillery explosions on the habitat of these whales, a series of 6.8 kg C4 plastique charges were detonated on land 500 meters from the waters edge. In addition to land seismic and acoustic arrays, hydrophones were deployed in the Knik Arm at high and low tide. This paper discusses the ocean acoustic measurements. The received signal 30 meters from the shore in water depths of 8 meters was more intense at high tide, with broadband peak levels of approximately 180 dB re 1 microPa. The dominant frequency was about 20 Hz and most of the received acoustic energy was below 500 Hz. The geology and oceanography of the area were used to model the acoustic time series. Modeled and measured time series are compared to validate the geophysical model and provide estimates of peak pressure and energy flux density over the near shore habitat. [Work supported by U.S. Army Corps of Engineers, CRREL.]