Granulometric dynamics of the coastal sediments of the Central West coast of India: Insight into morpho-tectonic influences on the beach processes

Abstract

Abstract Beach morphologies, primarily include shape, surface changes/variation, and beach volume along with slope, are very dynamic and believed to be largely controlled by waves and currents (Komar, 1998). Contrary to this general notion, results presented in this paper suggest a strong control of the local morpho-tectonic frame-work on foreshore sedimentation. In the 20\u202fkm long study area between Bhatkal on the north and Uppunda in the south, foreshore morphology range from reflective and dissipative to intermediate types, but nearshore hydrodynamic regime is similar. The inland morpho-tectonic frame-work reveals graben and horst-like structures. The foreshores bordering these grabens and horsts are dissipative and reflective respectively, have distinctly different granulometric dynamics and sedimentation processes, whereas an intermediate type between the dissipative and the reflective show a large seasonal variability in terms of beach width and slope. The foreshore profile modification indicated that the reflective beaches remained reflective and the dissipative beaches remained dissipative throughout the year, despite the large variation in the wave energy condition from monsoon through post-monsoon to pre-monsoon. Spit growth is observed only in the dissipative beach. Granulometric dynamics in all the three types of beaches show distinct differences. The reflective beaches show significant fluvial characteristics of sediments in all the seasons, dissipative beaches show minor fluvial characteristics and the intermediate beaches show significant fluvial characteristics only during the monsoon seasons. Sediment transport process in the reflective beaches is dominantly by rolling process, in the dissipative beaches suspension is the dominant mechanism, and in the intermediate type beaches a large range from suspension to rolling is observed. Sediments in the beaches are negatively skewed through symmetrical to positively skewed in reflective beaches, while in dissipative beach negative skewness is dominant. Integration of the tectonic framework, beach morphology and granulometric dynamics suggest that temporal and spatial variations in textural characteristics are related to a strong morpho-tectonic control rather than seasonal variations in wave energy condition.