Groundwater flow systems in the Bengal Delta, Bangladesh, inferred from subsurface temperature readings

Borehole temperatures were measured in observation wells to determine the temperature-depth profile, magnitude oftemperature and thermal gradient. The observed temperature profiles are classified into recharge and discharge types. Therecharge-type wells are located in the northern site of the study area. Meanwhile, discharge-type wells are found in thesouthern site of the study area. The 2-D cross-section of subsurface temperature shows that the shallow groundwater temperature in the southern discharge area is higher than that of the northern recharge area. The calculated temperature-depthprofiles for shallow wells show the recharge rate ranging from 0.04 to 1.35 m/year and discharge rate within the range of -0.2to -0.79 m/year. On the contrary, the recharge rate is 0.05 to 0.16 m/year and discharge rate -0.15 m/year for the deep well sites.The present study has revealed the existence of shallow and deep groundwater flow systems in Bengal Delta aquifers.