Spatial and temporal variabilities of groundwater characteristic distribution in the Nilwala River Basin

Abstract

The study was conducted in Southern Sri Lanka which is bound by longitudes 80.50 E and 80.59 E and latitude 5.59 N and 6.07 N in the Right Bank of Nilwala river Basin. This study aimed to identify corrective and behavior of the groundwater quality changers, present groundwater levels fluctuations with precipitation and groundwa ter consumption of the region. Groundwater is the major water source in the study area, where shallow uncon fined groundwater is used for domestic purposes and irrigation. To determine the hydrogeological conditions and groundwater quality distribution, conduct monitoring by selecting 60 (sixty) dug wells with respect to water level, electrical conductivity (EC), total dissolved solids (TDS), major cations and pH from January 2006 to May 2007. The dug wells are sunk into the permeable quaternary deposits overlying Precambrian granite gneiss and unconfined aquifer mainly consist with laterite and sandy clay.

The study helped to prepare hydro geological map and the distribution of EC, TDS and pH maps using the GIS package Arc view. Hydrogeological map help to identify recharge and discharge areas of the study area. The pH of the groundwater remains 4.5 – 6.5 and it usually decreases within a small range consequent to rains and EC fluctuation was in the range of 200 – 600 S/cm. Chemical analysis indicates that iron concentration is high in some areas which has more favorable situation for pyrite formation. The characteristic of hydrographs provide conclusion in the unconfined quaternary aquifer ground water level intimately related to atmospheric precipitation and recharge of aquifer takes place during the rain periods.