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HYDROGEOLOGY

Coastal Region:

The groundwater in the coastal region predominantly occurs under watertable conditions in the alluvial deposits of recent age and these aquifers are normally a few metres in thickness. Open wells of diametres of about 2 m are the common groundwater extraction structures. In some places the sandy aquifer may extend to depths of a few tens of metres. In such places, it is suitable to construct filter point wells. In some stretches, groundwater occurs in the upper tertiary sedimentary formations of Vaikom, Quilon and Varkkalai beds capped by laterites. In these areas, the groundwater occurs under artesian conditions. The piezometric surface of these confined aquifers has been found to vary between 0.5 to 14.3 m above msl. The wells with positive heads have a free flow of 270 - 360 Ipm. The Vaikom aquifers having thickness of 25 to 79 m are the highest groundwater potential aquifers in the coastal region. The sedimentary tract between Quilon and Sherthalai is suitable

for medium capacity tubewells.

Midland Regions:

In this region, groundwater is commonly encountered under water table conditions in the lateritic aquifers of about 10 to 20 m thickness. Dugwells of relatively large diameter of about 4 to 6 m are the common groundwater extraction structures in midland. The laterites are underlain by weathered rock and the two are usually separated by a lithomargic clay zone which is prone to caving and hence in such formation, laterite brick lining or concrete rings are necessary for open wells.

Ilighland Region

The jointed and highly weathered zone forms the aquifer in this region. Groundwater occurs under water table condition and the same can be exploited through dug wells. Deep seated fracture or fault zones in the hard rocks usually also hold groundwater and the same can be exploited through borewells. The plate shows in detail the hydrogeologic setup of Kerala (CGWB and State Groundwater Department).