Three-dimensional Modeling of Hydro-Thermal Structures in Lake Washington

A three-dimensional model—CH3D-Z—was applied to simulate the hydrodynamics of the Lake Washington—a deep, stratified temperate lake—over three-year period. The model was forced by winds and precipitation/evaporation as well as inflows from freshwater streams and the outflow through the lock connected to the Puget Sound. Surface heat exchange was also modeled. Realistic annual thermal-stratification cycle was simulated. The thermal structures were sensitive to the stability function of turbulence model related to Richardson number. We compared two approaches—one using non-equilibrium stability parameter and the other using empirical formulae. The former approach results in the better representation of the surface mixed layer depths. For the period of thermal stratification, mixing processes were studied by analyzing isothermal surfaces, buoyancy, and turbulence energy distribution. Basin scale motions represented by seiches and internal waves propagated through metalimnion showed typical response to wind forcing.