Estimating Water Flux in a Granitic Aquifer from Temperate Profile Measurements in Borewells of a Hard Rock Region, India

Abstract

Electrical conductivity (EC) and temperature logging were carried out in twenty-five borewells/piezometers in a hard rock region of Telangana, India at an interval of 1 and 2 m right from the water table till the bottom of the borewell to study the fracture zones at different depths and to recognize temperature variation with depths. The temperature and EC profiles of the groundwater were recorded at regular intervals along the depths of the borewells, the sensitivity of the sensor of the logger being limited to 0.1 K An attempt was made to calculate the vertical component of the water flux in 25 borewells using the temperature profile measurements in these borewells by applying the heat convection and conduction equation and taking into account the volumetric heat capacity of water and the thermal conductivity of rocks (in the present study, granite). The temperature data was first linearly fitted. The dispersion that would exist in thermal conductivity under the assumption as uniform flux for 22 of the borewell’s is unlikely, and data was fitted to the exponential trend of the temperature profile, considered to a non-zero water flux. This approach resulted in a comparatively better fit than the linear variation. Thus the water flux was calculated for 22 sites using the exponential variation relationship. It was found that the water flux ranges from 4 to 30 mm/year, which shows significant large variation from one location to other. It was also observed using the temperature measurements at the surface (from the temperature recorded at the meteorological station) that the temperature at depths is not affected by the variations at the surface, which confirms the reliability of vertical velocity/flow rate determination.