Numerical modelling of the riverine thermal bar

A Finite-Volume discretisation of the Navier–Stokes equations is used to study various aspects of the physics and ecology of the riverine thermal bar. The classical thermal bar is a down-welling plume which is formed twice a year in temperate lakes when the shallows warm or cool through the temperature of maximum density (Tmd). The riverine thermal bar is a similar sinking plume arising at the confluence of river and lake waters which are on either side of the Tmd. The dynamics of this poorly understood riverine case may be considerably more complex due to the additional effects of river salinity and velocity on the down-welling plume. A series of deep-lake simulations forms the initial study of the riverine thermal bar in the Selenga River delta in Lake Baikal, Siberia. While the decrease in the Tmd with depth (pressure) prevents the classical thermal bar from sinking far, this study shows that a saline riverine thermal bar may be able to sink to greater depths and thus take part in Baikal's vigorous deep-water renewal. Attention then focusses on a model of the smaller Kamloops Lake in British Columbia, which is used to reproduce the only field observations of a riverine thermal bar and test the effects of coriolis forces, bathymetry, and surface heating on the resulting flow field. Plankton ecosystem models are then coupled to these validated dynamics, and results are presented which extend and test the findings of a previous modelling study on the effects of the classical thermal bar on plankton populations.