Risk of seawater intrusion on coastal community of Bentota river basin Sri Lanka

Land degradation in coastal area is one of the major critical problems affecting the future economic development of Sri Lanka. Eighty percent of land in Bentota river basin has been abandoned and 25km distance along the Bentota river has already been affected by the seawater intrusion. Temporal and spatial variation of physicochemical parameters of selected dug wells, all surface water bodies and soil parameters were measured to detect the magnitude of the salinity due to seawater intrusion during August 2016 to March 2017 by using a systematic sampling method. Surface water, groundwater and soil salinity levels were comparatively very high in the river basin with respect to the WHO standards. With reference to the developed GIS salinity risk assessment weighted overlay model the highly saline, moderately saline, slightly saline and non-saline land extent with respect to the total land extent were 10.16%, 19.47%, 40.18% and 29.79% respectively. The highest economic loss was occurred due to the reduction of agricultural productions in the area (2279ha abandoned) and it was about 3,624,000 USD per year. Therefore, 52% from the total population was economically not active with the reduction of agricultural sector in the area. The total annual economic loss in the coastal community was 7,529,698.50 USD per year and it was directly happened due to the seawater intrusion.