Parameterization of bottom friction under combined wave-tide action in the Hooghly estuary, India

Abstract

A comprehensive knowledge of the wave climate is an essential pre-requisite for practical applications in coastal and near-shore region. In coastal areas the dominant dissipative mechanism appears to be bottom friction where the relative strength depends on bottom characteristics, sediment type and bottom ripple geometry. The present state-of-art version SWAN wave model uses three popular formulations for dissipative mechanism due to bottom interaction. The bottom friction coefficient as in SWAN cannot be a constant and needs to be tuned based on prevailing hydrodynamic conditions when applied for a tidal dominant region. A combined wave-current interaction study should take into account varying water levels, reversal of current system and associated shear on the sea-bed. The present work reports on development of a new resistance law for bottom friction under the combined action of waves and currents. This new formulation has been implemented in the SWAN model and further its implication on variability of significant wave height for the Hooghly estuary located in the Bay of Bengal, East coast of India was investigated by comparison with ENVISAT satellite measurement. Based on this study, it could be ascertained that new friction formulation has potential for wind-wave modeling studies in near-shore and coastal waters.