Water Shortage in the Lower Deduru Oya Basin

Abstract

Acute water shortage for agricultural, domestic, industrial and other activities is evident in the Lower Deduru Oya Basin (LDOB) due to changes in land use, abandonment of irrigation structures, extensive use of tubewells and lowering of groundwater levels. This situation has lead to a slowdown in the rate of agricultural development, weakening the socioeconomic activities and social milieu and also in controlling the improvement of living standards in the area. In the early 1990s, farmers had agro-wells dug in their own farmlands. Subsequently, farmers obtained water from shallow tubewells and then shifted to deep tubewells due to the lowering of the groundwater levels following micro-morphology. Many farmers have reported that turbidity, pollution and salt water intrusion are the major issues in tubewells. In some instances, high salt concentration in tubewell water has made extracting water for irrigation a problem. In order to evaluate the quality of water of the LDOB, the present study team examined the electrical conductivity, salinity and pH values of the water of 32 water samples from different locations. In some locations, for example, where the electrical conductivity is below 2000 and the salinity is also below 5.85, the water cannot be used for bathing and even for washing purposes. Laboratory analysis reveals that the salinity exists even in water samples obtained from tubewells that are 10-15m deep. The Deduru Oya Basin and its surroundings receive heavy rains during the 1st inter monsoon and 2nd inter monsoon and northeast monsoon periods giving surplus water. The trend lines of the average annual rainfall of the Deduru Oya Basin indicate decreasing trends, and are insufficient to maintain mega irrigation works such as the proposed Deduru Oya Reservoir as well as proposed hydropower projects, which will be expected to be completed by 2010. Nevertheless, even after the completion of the Deduru Oya Reservoir by 2010, the Ridibendi Ela, Magalla Wewa and LDOB will face water shortage. Consequently, the problem will be arisen seriously than at present, and that is not a relevant response to the water shortage in the LDOB area.