SEDIMENT BUDGET ANALYSIS AND THE ROLE OF SHORE PROTECTION STRUCTURES IN KOCHI COAST

Abstract

 Sediment movement is described in eroding Kochi Coast by using topography survey data in recent 25 years. The erosion is due to the sand exploitation from seabed and the decrease in sediment supply from two rivers. In the eastern zone, which is covered by the sediment from the Monobe River, a series of detached breakwaters appeared to stabilize the nearshore zone up to 500m from the seawall. The erosion was significant in the offshore zone with decaying rhythmic topographies. Sediment retention in reservoirs was significant and thus could compensate the erosion in offshore. In the western zone, which is covered by the sediment from the Niyodo River, the coastal sediment volume was found increasing, after the regulation of marine sand extraction. However, the speed of the sediment volume recovery was found to be small and the sediment volume in the downstream zone was found decreasing. Sediment bypassing and extension of headland works appeared to be effective in mitigating further erosion.