Tidal Energy Dissipation at the Sill of Sechelt Inlet, British Columbia

Abstract

The energy budget of a tidally active, shallow silled fjord is discussed. Constriction of the flow over the shallow sill causes a reduction in tidal amplitude and a phase lag across the sill. A generalized expression for the total power extracted from the barotropic tide by dissipation at the sill is derived as a function of the tidal amplitude difference and phase lag of the tidal elevation. Using tide gauge data from both sides of the sill at the entrance to Sechelt Inlet, British Columbia, this generalized expression yields estimates for the energy flux of the barotropic tide, which approach 100 MW during spring tides. From direct measurements of the currents, the estimated frictional dissipation is equal to the flux out of the barotropic tide (within experimental error). A small amount of the energy flux (?5%) is estimated to go into the generation of a tidal jet, which dissipates within a few kilometers of the sill and contributes to the formation of a mid-water layer.