An optimized combined wave and current bottom boundary layer model for arbitrary bed roughness

Abstract

Abstract : A robust method for computing the bed shear stress in unstratified combined wave and current flows is presented. The present approach follows from existing theories describing the nonlinear wave and current interaction in the benthic boundary layer but is designed for arbitrary wave, current, and roughness conditions, including the limiting case of pure waves or pure currents. The stress model is intended as a stand-alone application or for coupling to three-dimensional shelf circulation models, where a broad range of flow conditions are encountered. High-quality data for combined flows and pure waves are used with the present stress formulation to better refine empirical model closure constants in the fully rough turbulent regime. Introducing a first-order correction to the definition of the wave boundary layer thickness produces accurate estimates of both the measured friction factor and wave boundary layer height. A speed of convergence test indicates that the present model is more efficient than previous models that use the same turbulent closure scheme. This is primarily due to an improved solution algorithm that avoids the nested iterations common to established combined wave and current bottom boundary layer models.