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

J. P. Kukillaya ¹, K. Padmanabhan ², E. Krishnan ²

Affiliations
1 IX 695C, "Chetas", Erattakannanpalam, Talap, Pallikunnu P.O., Kannur, Kerala, IN
2 Kerala Samuhya Jalasechana Samithy, Thrissur - 5, Kerala, IN

Abstract

Short and medium duration pumping test data from a well-field, in conjunction with outcrop fracture pattern studies, are used to understand the nature of a system of fracture aquifers in a metamorphic terrain in Kerala State. Satellite imagery shows a minor E - W lineament intersecting a major regional NNW - SSE lineament in the area. Drawdown and time lag data indicate greater connectivity along the minor lineament compared to the major one. The E - W elongation of the drawdown contours correlates with dominant E - W fracture sets seen on outcrops. The NNW - SSE fracture zone probably forms a regional conduit for groundwater flow, with the degree of hydraulic. connectivity modified locally by other intersecting fracture zones. A large-scale heterogenity in the form of an E-W fracture zone is indicated in this area. The pumping tests give responses similar to double-porosity and semi-confined models. Some data suggest localised linear flow near pumped well. Heterogeneity in fracture distribution results in a complex response to pumping. Celtain broadly-defined zones and groundwater flow conditions are discernible within this heterogeneity.

Keywords

Groundwater, Fractured Aquifers, Hard Rock Terrain, Pumping Test, Kerala.

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J. P. Kukillaya ¹, A. Padmanabhan ¹, E. Krishnan ¹, K. Radhakrishnan ¹

Affiliations
1 Hydrogeologists, Kerda Samuhya Jalasechana Sanithi, Thrissur, IN

Abstract

Investigations involving satellite imagery studies, hydrogeological and geophysical surveys, fracture pattern studies, drilling, long duration pumping tests, water level monitoring, etc. provide an insight into the character of hard rock fracture aquifers, which are generally anisotropic and heterogeneous. Such investigations have helped ill delineating a fracture zone (Kalleppadanl-Oralassery fracture zone) near Pazhayannur in the Thrissur District of Kerala. The area forms part of the Precambrian metamorphic terrain with charnockite as the chief rock type. This fracture zone is one of the several NW-SE lineaments which represent groundwater-potential zones in Kerala State. Basic dykes intruding this zone are fractured. Although the phreatic zone consisting of laterite has low potential, the underlying two-layered fracture aquifers provide good yields through borewells of less than 80 111 depth. The aquifers are marked by steeply dipping fractures and dyke bodies. Pumping tests in a well-field have revealed the presence of poorly connected minor fractures within the major fracture zone. Test data from seven borewells have brought out features like similarity to a double-porosity model with a discontinuous fracture network, quick response of aquifers to pumping, possibility of temporary pressure build-ups in the aquifer during pumping. greater hydraulic connectivity along lineaments, a near-flat cone of influence etc. The double porosity model could consist of a few major fractures with associated network of minor fractures. The water table and the piezometric surface in the area show some similarity in the pattern of seasonal fluctuation.

Keywords

Groundwater, Fracture Aquifer, Hard Rock Terrain, Pumping Test, Water Level Fluctuation, Thrissur, Kerala.

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