Groundwater Resources in Walawa Basin
A.A.A.K.K.Seneviratne-Hydrogelogist, Water Resources Board,2A,Gregory’s Avenue Colombo 07
Introduction
Walawa is one of the most important River Basins in Southern part of Sri Lanka because major hydropower plant and irrigation schemes which make a significant contribution to food production and important nature reserves in the region are associated with it. Walawa Basin features a variety of water issues from massive irrigation development and increasing stress on the water environment to water quality and drinking water problems. The Basin is under going extensive changes due to agro ecological, Socio economic and institutional developments such as irrigation extension harbor expansion, construction of new air port projects.
Climate
A characteristics feature of the Basin is two wet seasons from the Northeast and South west monsoon with precipitation peak in April and November. The mean annual precipitation is 2050 mm with uneven spatial distribution. Despite the high precipitation, part of the Basin experience water scarcity problems during February –March and July October almost in every year. The amount of rainfall reduces from the upper reaches to lower reaches and from West to East of the catchment and shows high correlation with the elevation.
The mean annual temperature is about 32 0C with a fluctuation of 4 0C. The highest temperature was recorded during the month of July which is 37 0C while the lowest recorded on April around 270C.
Mean monthly relative humidity on average reported the highest, 89% and the lowest 60%. Generally the peak values achieve during the rainy period in January, February following the lowest in July, August. Difference between the monthly humidity in day time and night time is ranging from 30% to 10% for both stations.
Range of the average monthly pan evaporation of the catchment is changing 6.00 to 3.43 mmd-1. The highest pan evaporation is reported during the months of...