4.6. Wetting and Drying

The processes of wetting and drying have important physical and biological impacts on shallow water systems. Flooding and dewatering effects on coastal mud flats and beaches occur on various time scales ranging from storm surge, periodic rise and fall of the tide, to infragravity wave motions. To correctly simulate these physical processes with a numerical model requires the capability of the computational cells to become flooded and dewatered. Warner et al. (2013) proposed a method for wetting and drying based on an approach consistent with a cell-face blocking algorithm. The method allows water to always flow into any cell, but prevents outflow from a cell when the total depth in that cell is less than a user defined critical value. See Warner et al. (2013) for details.

The Wetting-Drying scheme is derived from John Warner’s code (Rutgers ROMS) and adapted to the time stepping scheme of CROCO. The main idea is to cancel the outgoing momentum flux (not the incoming) from a grid cell if its total depth is below a threshold value (critical depth Dcrit between 5 and 20 cm according to local slope; Dcrit min and max adjustable in param.h). This scheme is tested in the Thacker case producing oscillations in a rotating bowl for which an analytical solution is known.