Various geomorphic units of the Lower Long Sand -a dominantly sandy tidal shoal of the Bay of Bengal, have been delineated and studied with special reference to sedimentary structures and grain-size distributions. The bed forms and internal structures in each geomorphic unit are unique as regarding their time and space of formation and have been utilized in interpreting the flow dynamics and flow patterns.

The dunes are the most conspicuous structures of the dune field and supratidal zone and they readily point to a dominantly south-southwest direction of wind. The intertidal zone structures viz., swash marks, rhomboid marks and bicrestal ripples indicate a bipolar-bimodal flow pattern. The cross-ripples, capped-off ripples are important to indicate the interference of currents. The rill marks, current crescents and algal crescents form udder the dominant influence of backwash and point to unidirectional movement of water. The grain-size distribution curves of the intertidal zone sand- flats exhibit two saltation populations and reflect wave action under conditions of swash and backwash.