ASSESSMENT OF SEDIMENT TRANSPORT RATE AND SHORELINE EVOLUTION IN COASTAL ENVIRONMENT

Abstract

Muthalapozhy is a coastal outlet between towns Vizhinjam and Thangassery located at 8°38' N latitude and 76° 50' E longitude in Kerala State. This is the outlet where the Vamanapuram River drains off the water into the sea and the river is used as the navigational channel of the harbour. The outlet is gradually sifted up during early summer (i.e. in February and/or March) and gets chocked with sediment carried by the River and littoral current from the sea. During the south west monsoon, the backwaters along the coast are also flooded. To avoid floods in the area, the outlet of the river is artificially opened by dredging the littoral material. To make entrance channel operational throughout the year for navigational purposes, two rubble mound breakwaters were constructed. Despite of these structural measures used, the severity of the problem remained the same. In order to protect the area and keep the channel open throughout the year, a case study of alongshore sediment transport was undertaken using LITPACK modelling tool to model longshore sediment transport and shoreline changes along the coast and to find the optimum length of breakwaters. Sensitivity analysis shows that the sediment transport increases with the wave periods and in wave heights. With the increase in mean water level, sediment transport rate decreases exponentially. The littoral drift was found highly sensitive to the alignment of the shoreline. The estimated net littoral drift rate of 0.12x106 m3/year and using Energy flux (CERC) it was found to be 0.605X106 m3/year. It was also found that the transport rate is southerly during Southwest monsoon season (i.e. June to September) and northerly during rest of the year. Littoral transport rates calculated by energy flux method are having value of higher order as compared to model studies. In 2016, it is estimated that the cross-shore accretion on the south side of the south breakwater would be approximately 260 m from the shoreline. To make channel operational until 2016 without dredging, it is proposed to increase the length of the south breakwater by 200 m and the length of the northern breakwater by 70 m from the point of bend parallel to south breakwater. viii