Tidal flow over a sill in Muchalat Inlet, Nootka Sound, and the resultant mixing processes

Abstract

[author abstract] The tidal flow over Williamson Sill, situated in Nootka Sound, is analyzed by reviewing the changes in the density and velocity field across the sill and over the tidal cycle. The density is calculated from the raw data collected by UCTD casts while the velocity data was acquired from the ADCP. It was determined that the tidal forcing over the sill followed the ‘internal lee waves’ mechanism as opposed to the ‘stationary lee depression’ mechanism. During the first half cycle of ebb/flood, the lee waves were generated and held stationary downstream of the sill. These waves then propagated upstream when the tidal current started to wane. The interference of a propagating unsteady lee wave with a newly formed lee wave over the sill can cause wave breaking and substantial mixing.