Hydrodynamic stability of tidal inlet system: A case study of Pichaboni inlet, Purba Medinipur, West Bengal, India

Abstract

The hydraulic geometry of tidal inlets, like, cross-sectional area, wetted perimeter and hydraulic gradient is controlled by the dynamics of tides and wave-induced littoral drift along coastlines, pushing materials into the inlet during the flood tide and flushing them out during the ebb tide. An inlet which maintains its hydraulic stability has its velocity so adjusted that it can flush out all the materials pushed into the inlet. The Pichaboni inlet situated along the Bay of Bengal coast, is a linear channel and the tidal inflow is restricted by a sluice gate. This paper investigates the impact of hydraulic geometry, morphological changes and tidal behaviour on the hydrodynamic stability of the Pichaboni inlet. The longitudinal profile shows a reverse gradient from sea to inland. The smallest cross-sectional area (throat cross-section, AC) is located 672 m inland, which is slightly smaller than the cross-sectional area required to maintain the equilibrium flow velocity. Hence, the actual flow velocity through the throat cross-section is greater than that required for the equilibrium state, and the enlargement of the cross-section area may be caused by sediment scouring which decreases the flow velocity and leads to shoaling at the mouth. The dominant west to east longshore transportation brings a huge amount of sediment influx responsible for continuous sedimentation and the associated formation of spit at the inlet mouth. Any constriction at throat due to spit formation leads to accelerated flow velocity associated with scouring at the throat area and breaching of the spit. This results in the gradual shifting of the inlet mouth by the mechanism of bar by-passing. The economic importance of the main inlet channel and its adjacent intertidal basin necessitates evaluation of the long-term stability of the tidal inlet through analysis of hydraulic and sedimentary characteristics of the inlet.