Journal of Geological Society of India (Online archive from Vol 1 to Vol 78)

R. N. Athavale ¹, R. Rangarajan ¹, D. Muralidharan ¹

Affiliations
1 National Geophysical Research Institute, Hyderabad, 500 007, IN

Abstract

The broad pattern, emerging from recharge measurements in various basins ranging in area from few tens to few thousands of square km indicates an annual input of about 16% (or 100 mm) of the precipitation in the Indo-Gangetic alluvial tract and about 8% (or 60 mm) ofthe precipitation in the Peninsular hard-rock areas. The Tritium recharge measurements are compared with those obtained by using hydro-meteorological and hydrogeological methods. The relation between recharge values and water level fluctuations in open wells is studied and regression plots showing dependence of recharge rate on rainfall over granitic, basaltic, sedimentary and alluvial provinces are presented. Data on temporal variation in recharge due to variation in rainfall over three hydrological cycles in a granitic watershed in the semi-arid area is presented. The utility of such studies in prediction of recharge from rainfall data is illustrated.

Keywords

Hydrogeology, Groundwater, Rainfall, Recharge, Tritium.

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D. Muralidharan ¹, G. B. K. Shankar ¹

Affiliations
1 National Geophysical Research Institute, Hyderabad - 500 007, IN

Abstract

An attempt has been made to extend the empirical relationship between geoelectric parameters and hydraulic properties of an aquifer put forth by Kelly (1977) for the phreatic aquifers of Deccan Trap basalts. Results of pumping tests, resistivity surveys and hydrogeochemical analysis from Godavari-Purna basin were utilised. A linear relationship between Transverse Resistance and Transmissivity of phreatic aquifer was obtained. The linear relationship was extended to other similar basaltic areas for validation.

Keywords

Hydraulic Transmissivity, Resistivity, Deccan Traps.

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D. Muralidharan ¹

Affiliations
1 National Geophysical Research Institute, Hyderabad - 500 007, IN

Abstract

Resistivity sounding technique is conventionally adopted for ground water exploration in hard rock areas. From the interpretation and layer parameter evaluation alone, deciphering the actual depth to aquifer zone and delineating the thin high yielding fracture zones is found to be difficult. In many cases, the high yielding zones are found to be well within the bedrock signal part of the sounding curve. A non-conventional way of examining the apparent resistivity data of soundings was attempted for the soundings conducted over different hard rock terrains. The interpretation yielded a factorial depth relation with the yielding aquifer zones hidden in the bedrock signal. This approach has been used successfully in many areas of investigation. A theoretical base for the observed depth relation is at developmental stage.

Keywords

Apparent Resistivity, Aquifers, Hard Rock Terrains, Factor Function.

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D. Muralidharan ¹, R. Rangarajan ¹, G. K. Hodlur ¹, U. Sathyanarayana ¹

Affiliations
1 National Geophysical Research Institute, Hyderabad - 500 007, IN

Abstract

A research study has been carrted out to evaluate the economically viable depth of desiltation in old tanks to achieve a substantial increase in percolation and storage Two tanks -an old minor irrigation tank and a newly constructed percolation tank were selected in a granite terrain and infiltration studies were carried out with different thickness of silt removal Tritium tracer studies were coupled with the infiltration studies to follow the infiltrated water and evaluate the effectiveness of silt removal in percolation The study lndicated that in the case of irrigation tank, a steady state infiltration rate of 67 mm/h has increased to 350 mm/h with the removal of 65 cm silt showing a six-fold increase in infiltration rate Infiltration rate was found to be reducing by removal of 25 vm and 50 cm silt and the analysis of soil fraction indicated presence of clay at these depths The study at percolation tank indicated that the infiltration rate of 10-20 mm/h has increased to a maximum of 310 mm/h with removal of 40 cm silt The tritium tracer migration study supported a faster movement of percolated water at desilted sites by showing a greater dilution of tracer concentration and deeper penetration The research study strongly supports a necessity of carrying out infiltration studies at different places within the tank bed area with removal of varying thickness of silt to decide the optimal level of desiltation especially in old tanks before commencing revival of tank system.

Keywords

Tanks, lnfiltration rate, Optimal desilting, Percolation efficiency, Anantapur District, Andhra Pradesh.

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