Quality of Irrigation Water in Sri Lanka – Status and Trends

Article type: Research Article

Authors: Silva, E.I.L.

Affiliations: Institute of Fundamental Studies Hantana Rd, Kandy, Sri Lanka. E-mail; sil@ifs.ac.lk

Abstract: Already available and newly collected data sets on water chemistry of twenty reservoirs located in seven river basins in Sri Lanka were analyzed to determine the status and trends in irrigation related water quality characteristics. pH of irrigation water varied within a wide range but the upper limit did not exceed the proposed level suitable for irrigation water. Salinity was found beyond the threshold level (1.250 g l^{-1}) only in two reservoirs located downstream of the Malwathu Oya basin and the electrical conductivity had never reached above 1 mS cm^{-1}. Sodium absorption ratio (SAR) was well below the threshold value of 6 meq l^{-1} in the study reservoirs. Least square regression model showed that electrical conductivity was a good predictor of salinity and SAR. Time series data showed no marked changes in irrigation water quality of the reservoirs located in the Mahaweli river basin over the last forty three years with respect to EC levels but the EC of those proximate reservoirs receiving additional transfer water from the trunk stream of the Mahaweli river showed a progressive decrease following the trans basin diversion.

Keywords: Irrigation reservoirs, salinity, SAR, basin transfer, Sri Lanka

Journal: Asian Journal of Water, Environment and Pollution, vol. 1, no. 1-2, pp. 5-12, 2004