Sand Waves in Lower Cook Inlet, Alaska

Abstract

Acoustic (geophysical) methods were applied to investigate the sea-floor geological conditions, particularly sand waves, which might place constraints on construction in an area of potential offshore development in lower Cook Inlet, Alaska. Multisystem, high resolution, marine acoustic survey data were collected using a sparker, tuned transducer, acoustipulse, fathometer, and side-scan sonar. Based on 65 sea-floor samples obtained in the northern portion of the study area, the sea-floor soils consisted of over 90 percent sand by volume. This portion of lower Cook Inlet contained the most numerous sand waves and contained sand waves of 5 ft (1.5 m) or greater height over an 80 percent length of the survey lines. The possibility of sand wave movement is examined by reviewing the two phase (water-sand) flow regime and by repeat geophysical profiling. The present flow regime appears to be conducive to the formation of ripples and dunes, but tidal flow durations may be insufficient for the formation of large bedforms.