Wave-induced nearshore flow patterns in the vicinity of Cochin harbour, India

Abstract

The wave-induced nearshore circulation and the sediment exchanges between two littoral cells along the beaches bordering Vypeen and Chellanam islands in the vicinity of Fort Cochin are examined. In general, the flow within this narrow zone consists of a sheared cellular flow pattern with clockwise and anti-clockwise rotations exhibiting noticeable spatial variation. Field studies reveal a southerly littoral current during most of the year. A conceptual model is presented to explain the sediment movement along the two littoral cells. The sediments introduced to Vypeen littoral cell are transported southwards by the incident waves either in the form of cellular or meandering flows, depending upon deep water wave approach. The strong flows associated with the tide in the Cochin harbour entrance channel obstruct transport further south. During the monsoon season, sediment from either side of the channel is transported into the channel under the influence of the clockwise and anti-clockwise circulation cells. In the CheUanam littoral cell inadequate sediment supply coupled with strong littoral flows make the beaches vulnerable to continuous erosion.