Tidal variation and flow dynamics in Indian Sundarban based on field observation and numerical models

• Published in: Estuarine, coastal and shelf science coastal and shelf science, 2024-09, Vol.304, p.108851, Article 108851
• Main Authors: Paul, Swapan, Das, Chandan Surabhi, Chaudhuri, Subhamita
• Format: Article
• Language: English
• Subjects: Current speed; Hydro-geomorphology; Mike 21 FM; Tidal asymmetry; Tidal harmonics
• ISSN: 0272-7714; 1096-0015
• DOI: 10.1016/j.ecss.2024.108851

Sundarban is made up of a mesh of macrotidal estuarine systems that contain the world's largest mangroves, the eco-geomorphic environment of which is heavily influenced by tidal behaviour and flow characteristics. The present study aimed to identify the tidal attributes and document the flow character of Indian Sundarban throughout a fortnightly tidal cycle. As such, seven tide monitoring stations were installed across the Saptamukhi-Hariabhanga and connected river system to monitor tidal water levels. Based on this data, the Institute of Ocean Sciences' (IOS) method was used to extract 17-major tidal harmonic components to study the links between various oceanic and shallow-water tidal constituents that may contribute to tidal asymmetry. A Mike-21-flow model was also run to simulate the tidal flow of the regime. Result shows that the progression and convergence of tidal waves in the funnel-shaped estuarine system causes notable lag between the southern and northern limits (avg. 45 min over a 52 km-long stretch of Thakuran estuary). The harmonic components indicate that semi-diurnal M2, S2; over tide 2MS6; and diurnal O1, K1 are the major forces, shaping the tidal amplitude in this region. The third, fourth, and sixth diurnal constituents represent additional tidal components, although with relatively minor amplitudes. The transition from coastal to headward stations sees a shift in the relative phase from 93.73° to 96.17°, suggesting a flood dominance and minimal dissipation of energy within the system. Mike-21FM found that the spring flood-current speed with an average value of 0.42–0.56 m/s is significantly higher than the ebb current of averaging 0.25–0.32 m/s. The nature of neap tidal current speed in the Sundarban region generally mirrors that of the spring condition, although with much less intensity. We assume that since any bi-weekly hydraulic analysis has not yet been conducted in Sundarban, it may be highly valuable for future studies. •First-ever biweekly analysis of tide and tidal flow in Indian Sundarban.•IOS and Mike.21 FM models validated with field data in numerical study.•Identified 17 tidal elements; region interpreted as semi-diurnal; flood dominated.•Flood-driven tidal system deposits in inner areas, erodes near edges.