Wave Attenuation Due to Bottom Friction across the Southwest Indian Continental Shelf

Abstract

The energy of any coastal zone is dependent on the wind generated waves in the offshore and their transformation in shallow water controlled by processes such as refraction, shoaling and bottom frictional attenuation. In examples described from the southwest coast of India, the loss of energy due to bottom frictional attenuation, though neglected sometimes, plays a major role in shaping the coastal wave climate. The study has been carried out for three selected locations with varying bottom slopes and sediment characteristics along this coast using a wave refraction model. Though there is significant difference between shelf sediment characteristics of the southern and other parts of the shelf, a friction factor of 0.02 seems to account well for the attenuation. The energy loss due to bottom frictional attenuation on the northern (gently sloped) coast is much greater than on the southern (steep) shelf. This predicted variation agrees with the observed distribution of wave energy as determined from wave measurements along this coast. The study underlines the importance of shelf slope in controlling spatial contrasts in bottom frictional attenuation and consequently the coastal energy regime.