THE MORPHOLOGICAL, ENVIRONMENTAL CHANGES AND STABILITY OF THE SEA AND RIVERBEDS LINKED WITH HARBOUR DREDGING

摘要

Enormous amount of mud and sand are dredged out to maintain the outer channel as a passage for large vessels to Kochi (South west India) port. The mud and sand dredged out is eventually dumped at the extreme northern and southern ends of the channel, used as dumping grounds. For a proposed oil terminal, the channel have to be dredged at lest another five meters, raising the amount dredged from 11 million cubic meters to an alarming (25 - 30) million m~3. The morphological changes and stability of the sea and riverbeds were studied at 44 stations in and around Kochi harbor, covering an area of 13 km~2 of estuarine and near shore areas (including the proposed dredge spoil dumping sites). Benthos serve as sensitive indicators of long-term effects or short-term perturbations either natural or man-made. The physical removal of incumbent population along with dredge spoil, the fauna will be exposed to new substratum and to changes in the nature of substratum. The study showed that dredging resulted in a decrease of population density. The recovery of the total numbers of individuals was faster than that of total number of species. The diversity of species was considerably high. Only few polychaete species were replaced by some other species. This might be due to slight variation in the environmental factors and food resources. The fauna seemed to be exposed to new temporary substrata having the same sediment characteristics holding high organic content. The 5 decades of dredging has not shown any signs of serious impairment. The present and proposed dredging and dumping areas are comparable in environmental and sediment characteristics - the envisaged increase in the quantum of material dredged and disposed is unlikely to cause detrimental environmental changes in the harbor and near shore regions.