High-frequency backscatter measurements of coastal dynamics in Haro Strait

Abstract

The Straits of Georgia and Juan de Fuca near the British Columbia and Washington state coasts form an estuarine system through which Fraser River runoff empties into the Pacific. Most mixing between the fresh surface water and deeper Pacific inflow occurs during spring tides in the narrow connecting channel of Haro Strait, leading to a 2-week periodicity in mean stratification. However, coastal and estuarine environments are characterized by complex and rapidly changing structures with scales of meters to kilometers which are difficult to observe with conventional techniques. Thus little progress has been made in understanding the details of mixing in Haro Strait. However, the rapid surveying capabilities of acoustic Doppler current profilers, volume imaging echo sounders, and surface scattering side-scan sonars enable the formation of nearly instantaneous snapshots of various stratified flow effects. These include frontal formation and decay, shear flow instability and sill hydraulics. In June/July 1996 these instruments were deployed from ships, drifters, and autonomous underwater vehicles to better understand the mixing processes in this area. [Work supported by ONR.]