CMS-Flow:Salinity Calculation

CMS-Flow: Salinity Calculation (V3.75) - UNDER CONSTRUCTION

Introduction

In many estuaries, the density gradients caused by spatial variations in salinity can be an important driving force in the circulation. Salinity is also a key water quality variable in estuaries, since it affects the chemical and biological processes. Salinity is simulated in the Coastal Modeling System (CMS) in a depth-averaged sense. This means that the estuary or body of water is assumed to be well mixed vertically and the salinity is constant over the water column.

Governing Equation

The depth-averaged 2-D salinity transport equation is given by

        ${\frac {\partial (hC_{sa})}{\partial t}}+{\frac {\partial (U_{j}hC_{sa})}{\partial x_{j}}}={\frac {\partial }{\partial x_{j}}}{\biggl [}K_{sa}h{\frac {\partial C_{sa}}{\partial x_{j}}}{\biggr ]}$

where $t$ is time, $U_{j}$ is the current velocity in the jth direction, $h$ is the total water depth, $C_{sa}$ is the salinity concentration, and $K_{sa}$ is the salinity mixing coefficient.

Initial and Boundary Conditions

The initial salinity is specified as a constant in the whole domain. The value of the constant is specified in the SMS 10.1 interface. Inflow salinity concentrations are applied at specified salinity boundary cell strings. Salinity cell strings are specified in the same manner as the hydrodynamic boundary cells strings.

Numerical Methods

The salinity transport equation is solved with an explicit, finite volume method. The advection term is discretized with upwind scheme, and the diffusion term is discretized with the standard central difference scheme.