3-Soil Moisture Studies for Ground Water Resources Evaluation.

Abstract

Soil moisture and soil physical studies are useful in evaluating the groundwater resources for estimation of actual evapotranspirational losses & specific yield of the shallow aquifer zone, to quantify the soil moisture storage variations useful for water balance studies & agricultural operations, and to understand the mechanism of recharge to ground water through the unsaturated zone & to quantify the same. Two case studies giving the details and results of the soil moisture and soil physical studies carried out by the Central Ground Water Board (i) in the upper Betwa river basin, Madhya Pradesh under the Indo-British Betwa Ground Water Project and (ii) in the Chinnatadgam, Avanashi Upper Vattamalaikarai sub-basins of Tamil Nadu & Kerala, under the SIDA assisted Groundwater Project, have been presented. The studies in the upper Betwa river basin showed that (i) the actual evapotranspiration during the period 14-10-77 to 2-6-78 is 307.1 against the calculated potential evapotranspiration was about 31% of PET. (ii) the specific yield of different depth zones upto 2.5m varied from 1.36% to 0.48% and (iii) in case of areas with deep soils the structured clay 'black cotton soil' forms an upper aquifer system which is virtually isolated from the more conductive weathered basalt aquifer beneath by the intervening thickness of unstructured and poorly conductive yellow clay. Studies in the Chinnatadgam; Avanashi & U. Vattamalai Karai sub-basins indicated that (i) the specific yield of soil layers varied from 6.2 to 19% (ii) the average actual evapotranspiration in these 3 sub-basin is 0.71mm / day, 0.79mm / day and 0.55mm / day respectively and (iii) the final rate of infiltration varied from 5 to 150mm / hr for black soils, 40 to 190mm I hr for Red insitu soils and 20 to 390mm / hr for colluvial and alluvial soils.