A Numerical Model of the Circulation in Knight Inlet, British Columbia, Canada

Abstract

During spring 1988 (a period of low freshwater runoff) and summer 1989 (a period of high freshwater runoff), month-long observations of velocity, temperature, and salinity were made throughout the water column in Knight Inlet, both up-inlet and down-inlet of the sill. Measurements were made at depths of 2, 4, 6, 9, and 12 m using S4 current meters, at depths down to about 200 m using profiling current meters, and at depths deeper than 200 m using Aanderaa current meters. Anemometers were deployed at two locations along the inlet. A laterally integrated, two-dimensional numerical model of the inlet that uses the Mellor and Yamada level 2.5 turbulence closure scheme and that accounts for the combined influence of the winds, tides, and freshwater runoff has been used to produce 30-day simulations of the velocity and density field in the inlet. The vertical coordinate is transformed in the model so that very fine vertical resolution can be attained near the surface even though the tidal range is large. Therefore, the thin but distinct, surface layer that exists in the inlet during times of high, freshwater runoff can be resolved by the model. With a single set of empirical constants, that is, horizontal diffusion and drag coefficients, the model successfully reproduces much of the tidal, estuarine, and wind-forced components of the circulation in the inlet during the two observation periods, as long as the vertical diffusion coefficients of Mellor and Yamada are augmented by an extra stratification-dependent term. This term can be interpreted as representing the mixing caused by breaking internal waves.