Establishing morpho-dynamic baseline for flow-sediment management of a tidal river in the Ganges–Brahmaputra–Meghna Delta system through field measurement.

In tidal environments, implementation of sustainable erosion management and land reclamation programs demands prior understanding of morphodynamic baseline. To address this, detailed field measurements along a tidal reach of the Pyra river in the Ganges–Brahmaputra–Meghna (GBM) system followed by systematic evaluation of associated flow-sediment parameters are presented here. Different sensors such as Eco-sounder, ADCP, OBS, and GPS coupled with total station were deployed to measure the spatial and temporal nature of flow and sediment transport related parameters. The measurements reveal that the tidal amplitude varies between 1.25 to 2.5 m (daily) and 1 to 1.25 m (seasonally), while, the maximum ebb and flood discharges varies between 3640–3860 m³/s and 2500–3060 m³/s respectively, peak ebb and flood velocities varies between 0.62–0.64 m/s and 0.38–0.45 m/s respectively with ebb period 8 h and flood period 4 h. Accordingly, the estimated bed shear velocity (5–8 cm/s), is found greater than threshold for erosion and suspension (1.2–1.3 cm/s for bed materials and 0.80–0.82 cm/s for bank materials respectively). Further, the measured SSC varies between 725 and 750 mg/l during ebb and 480–540 mg/l during flood. The above baseline data revealed the site as ebb dominating and hence in every cycle, the net residual current and sediment moves towards the seaward direction, and hence, sediment trapping potential will be higher during ebb phase. These findings will be useful to devise effective sediment management strategy for tidal river and to calibrate and validate related numerical models within the GBM system. Plain language summary: Stronger fluid force causes significant erosion and suspension of very fine bed and bank materials and moves mostly as suspended load. Erosion > deposition in a tidal cycle and net undeposited sediment transport occurs in seaward direction as the site is ebb dominated. Erosion management and land reclamation strategy may be achieved by managing this sediment through appropriate structural intervention. [ABSTRACT FROM AUTHOR]