An Effective Algorithm to Reduce Horizontal Pressure Gradient Errors in σ-Coordinate in EFDC Hydrodynamic Model

Abstract

Abstract Environmental Fluid Dynamics Code (EFDC) is a three-dimensional sigma coordinate hydrodynamic model coupled with a water quality model. The EFDC model has been used worldwide in environmental modeling of surface water hydrodynamics and transport. The EFDC model employs a vertical sigma-coordinate transformation to deal with irregular water depth. This coordinate transformation introduces additional terms in horizontal pressure gradients. It is well known that direct numerical discretization of the full sigma-transformation of the horizontal pressure gradient produces numerical errors when a steep bottom slope exists. Errors in pressure gradient calculations can cause errors in velocity field and ultimately can result in spurious transports. In this study, an effective numerical algorithm is presented to reduce numerical errors induced by the horizontal pressure gradient term in the sigma coordinate. The transformed pressure terms in the sigma coordinate are discretized in sigma grids into the sim...