Quick Quantitative Appraisal of Groundwater Resources - Case Study on 'Coconut Triangle', Sri Lanka

Based on different methods of quick quantitative appraisal, the recharge to the groundwater body is estimated to be around 150 mm per unit area per annum. The potential evapotranspiration varies from 1170 mm to 1340 mm. The run off is about 1 MCM per sq. km per annum in the Maha Oya basin and decreases to 0.4 MCM per sq. km per annum in the Deduru Oya basin. Unclassified granite gneisses, khondalites and charnockites occur over alargc part of the area. Groundwater occurs in the weathered and fractured parts of the hard rocks and in the intergranular pore spaces in the Quaternary formations under unconfined to semi-confined conditions. The water levels vary from 1 m to 15 m below ground level. The groundwater recharge occurs two times in a year - in May-June and again in November-December. The quality of water is good with tbe electrical conductivity being Jess than 300 micromhos/cm at 25°C.