Characteristic Responses to Pumping in Hard Rock Fracture Aquifers of Thrissur, Kerala and their Hydrogeological Significance

Pumping test data in the hard rock fracture aquifers of Thrissur district has revealed certain characteristic responses. Thirtytwo percent of the test data shows simultaneous recharge to the aquifer during pumping. Interconnection between phreatic and fracture aquifers and recharge from the phreatic zone to the fracture zone are indicated. Responses similar to double-Porosity model are attributed to probable large variations in fracture scales. Another characteristic response is that of a continuous slope increase in semi-Log plots of drawdown, indicating linear fracture zones with barrier boundaries on both sides. Geological features and good fracture connectivity support this inference. Similarity with the response of a homogeneous anisotropic aquifer is also seen when responses over a large area are considered. Large spatial variations in specific capacity indicate heterogeneity. Tests suggest turbulent flow around pumped wells. Small-Scale fracture networks and the phreatic zone probably have a greater role in determining the groundwater potential of hard rock areas as compared to the few large-Scale fractures. The responses suggest that the fracture aquifers in the area have only limited potential.