International Research Journal of Environment Sciences________________________________ ISSN 2319–1414Vol. 4(9), 39-44, September (2015) Int. Res. J. Environment Sci. International Science Congress Association 39 Hydrological Interaction between Surface Water and Ground Water in Vavuniya District of Sri Lanka Tharani G1*, Nanthakumaran A. and Karunainathan T.2 Department of Bio-Science, Faculty of Applied Science, Vavuniya Campus, SRI LANKA Agriculture Research Station, Dept. of Agriculture, Thirunelvely, Jaffna, SRI LANKA Available online at: www.isca.in, www.isca.me Received 6th June 2015, revised 9th July 2015, accepted 16th August 2015 AbstractIrrigation tanks are the only surface water resource in Vavuniya district. Households in this district are dependent on ground water sources to satisfy their domestic water needs. It has been experienced and reported by the households that the wells during the dry season especially during the months of June, July, and August became dry without water while there was little water in the irrigation tanks in this district. Hence, this study was carried out to understand the hydrological relationship between surface water and ground water. Three tanks namely Vavuniya tank, Pandarikulam tank and Paddanichchepuliyankulam tank were purposively selected as surface water source. 21 wells were selected from each Vavuniya tank and Padanichchepuliyankulam tank command area and 23 wells were selected from Pandarikulam tank command area as ground water source. The measurements of water level of tanks and wells were taken once in two weeks for six months from August 2013 to January 2014. The correlation coefficients of respective tank water levels Vs well water levels were estimated using Minitab 16 and found that the average correlation coefficient of the same of Vavuniya tank, Pandarikulam tank and Paddanichchepuliyankulam tanks were 0.88, 0.72 and 0.69 respectively. The strong positive correlation between the tank water level and well water level in the selected tanks confirmed that the increased tank water level would ensure the well water level. Any action taken towards tank maintenance and rehabilitation would ensure the sustainable water availability in the wells. Therefore maintaining sufficient water level in the tank would help to minimize water scarcity issues in Vavuniya. Keywords: Correlation coefficient, irrigation tank water level, water scarcity, well water level. Introduction Ground water resources and recharge rates shows variation across Sri Lanka locally and regionally. Different geologic formations retain water differently. Vavuniya district falls in the metamorphic hard rock region of the dry zone of Sri Lanka. The groundwater present in this region made up of the shallow ‘Regolith Aquifer’ and the deeper fracture zone aquifer. This ground water found in an irregular pattern in crevices and fractures within rocks with distinct water table. In Vavuniya, the ground water system is controlled by the small tank cascade system designed for increasing surface water availability. Vavuniya is mainly an agricultural district where people use surface and ground water for cultivation. Ground water sources satisfy the domestic needs of the households in this district. Vavuniya district experiences an acute shortage of drinking water during the dry season and the water supply to the region was not sufficient to meet the demand. There are one major, 21 medium tanks and 674 minor irrigation tanks including 26 anicuts distributed in Vavuniya district. The water resources mainly depend on rainfall as there are no perennial rivers. Out of the 674 Minor Irrigation Schemes, 41 abandoned tanks, 64 breached and nearly 208 tanks to be renovated During some periods in a year, the wells in some residential area are dried completely. Thus, the determination of hydrological interaction between surface water level and ground water level in Vavuniya district was considered important for determination of well water recharge by surface water in regolith aquifer. The objective of this study was to find out the correlation between tank water and well water. Methodology Among 674 tanks found in Vavuniya district, three tanks were purposively selected; Vavuniya tank, Pandarikulam tank and Paddanichchepuliyankulam tank which are closer to each other to ensure similar topographic and climatic conditions. The sample wells were selected sequentially along the water flow path using Google earth pro. To ensure maximum coverage of tank water flow number of wells were chosen sequentially each side of the water flow in the command area. The details of sample tanks and number of wells selected for each tanks were given in table-1. Wells and tanks were mapped in Google earth pro with coordinates obtained from GPS. Well water level and tank water level were measured once in