Tidal and non-tidal components of water level and currents in the Sundarbans ecosystem

Abstract

The present study is an effort to understand the complex tidal characteristics and flow conditions at Kaikhali station located in the Matla River of the Indian Sundarbans ecosystem. The study region is located south of the low-lying Ganges–Brahmaputra deltaic environment that is highly vulnerable to the impact of sea level rise. The maximum recorded tidal range at Kaikhali location is about 6.35 m, and the current speed varied between 0.03 to 1.18 m s−1 with an average speed of 0.48 m s−1 during the observation period. The currents closely followed the flood and ebb phases of the tidal cycle with a maxima recorded during the spring high tide conditions. The predominant current direction was northeast (NE) and southwest (SW) during the flood and ebb phases of the tidal cycle, respectively. The tidal characteristics are semidiurnal in nature, and among the five major tidal constituents M2, S2, K1, O1 and N2, the relative influence of principal lunar (M2) and principal solar (S2) components contributes 58% and 25%, respectively. The circulation characteristic in this ecosystem is a result of the combined effects of freshwater discharge from riverine tributaries, creeks and tidal propagation from the open sea. A detailed investigation performed in the present study using the measured data signify that the tidal currents dominate as compared to the non-tidal components in this region. The study has practical applications in understanding the estuarine hydrodynamics over this region.