Chapter 9 - Temporal Trends of Breaker Waves and Beach Morphodynamics Along the Central Tamil Nadu Coast, India

Abstract

Breaker wave type and the beach's morphodynamic state are the commonly deployed parameters that portray the nearshore wave climate and beach morphology with respect to monsoonal conditions. This chapter presents an analysis of the temporal variability of breaker wave type and beach morphodynamic state, and their impact on foreshore and nearshore dynamics along the 51-km coastal stretch between Thirukadaiyur in the north to Velankanni in the south, on the central Tamil Nadu coast in southern India. The area experiences three seasons in a year; southwest (SW) monsoon (July to October) season, northeast (NE) monsoon (November to February) season, and fair weather periods (March to June). A field survey was conducted along the study area on monthly basis between January 2011 and December 2011, and a seasonal basis between January 2012 and January 2013, respectively. Wave parameters such as breaking wave height, wave period, and foreshore slope were measured with conventional measurement techniques and tabulated for empirical analysis. Sediment samples were collected in the foreshore region and subjected to conventional granulometric analysis. The observed wave data reveals that the wave period and foreshore slope were positively correlated, while breaking wave height was negatively correlated. The effective breaking waves at full force enabled maximum erosion during the NE monsoon season, while the low-energy waves promoted accumulation of sediment during the SW and nonmonsoon periods. By using the field data, breaker wave type and beach morphodynamic state were estimated to evaluate the seasonal influence on beach and wave dynamics on a temporal scale. The graphical results show that the study area has experienced a dissipative morphodynamic state with spilling breakers during the northeast (NE) monsoon season, an intermediate state with plunging breakers during the fair weather period, and a reflective state with surging breakers during the southwest (SW) monsoon season. It was suggested that seasonal action influenced modelling the beach shape, wave propagation, sediment size distribution, and topographically induced nearshore circulations. A strong correlation between sediment sorting and the morphology of the beach was verified by the grain size distribution present in the coast. It was also revealed that the seasonal variation and reworking of sediment transition stabilize the equilibrium beach condition.