Subsurface Flow of Water and its Structural Control in the North Ganges Floodplain of Bangladesh

The surface configuration of the north Ganges floodplain, covering the region Godagari. Rajsbahi (Paba-Boalia), Durgapur, Puthia and Charghat has been determined. The central region of the investigated area shows some prominent north-south elongated elevated zones and an east-west elongated depressed zone. The rest of the investigated area is marked almost by the flat and sloping surface. The subsurface structural configuration has been inferred taking into account the prominent basement faults and the regional geologic cross-sections. It is inferred that the investigated area is located on the downthrown segment bounded by faults. However the region located nearCharghat where the river Ganges has taken almost 90° swing, is relatively an uplifted block.

The occurrence and the flow of grownd water in the investigated area have also been determined. The area covering Paba-Boaliaand Godagari is characterized by short distance recharge and infiltration from the near surface sources for the groundwater occurrence and movement, while the occurrence and the movement of groundwater in the region of Charghat, Puthia and Durgapur depend on the long distance recharge and infiltration from a few near surface sources.

The water table coutour maps both for the dry and the rainy seasons show some prominent diverging patterns. The water table fluctuation map shows that the zone of minimum fluctuation coincides with the zone characterized by diverging pattern. This anomalous situation has been interpreted as due to relatively higher hydrostatic pressure and the existence of an effective barrier of clay of about 50 feet thick oriented in the north-south direction across Charghat, between Soalia and Puthia, and between Paba and Durgapur.