Assessment of Aquifer-Land Use Composite Vulnerability in Walawe River Basin, Sri Lanka

In the present study, DRASTIC model has been used as a feasible methodology to assess the groundwater vulnerability in the Walawe river basin, Sri Lanka. Geographical Information System (GIS) has been used to develop vulnerability maps, explaining the relative vulnerability of the area. The DRASTIC output concluded that the upper and western parts of the basin show very low vulnerability while the lower part shows higher vulnerability. The groundwater vulnerability maps are compared with the agricultural land-use pattern of the area and it is noticed that the intense agricultural areas and high DRASTIC index areas are overlapped. To emphasise the natural state of the aquifer media as well as the potential pollution of extensive land use, a new indicator has been introduced as Aquifer-Land use Composite Vulnerability Index. This indicator further concludes that the lower part of the Walawe River basin depicts a higher risk for future groundwater quality and hence more attention should be focused to establish monitoring network for adequate groundwater quality control in the area.