Abstract:
Vavuniya district of Sri Lanka consists of nearly 674 minor irrigation tanks which are in a cascade system supplying water for 10900 ha (10900 × 104 m2) of paddy land. But there is no documentation available for the cascade systems. In the recent past effort was taken to rehabilitate some of those tanks with the available source of funding. Since there is hardly any knowledge on the pattern of those cascades, the tanks for rehabilitation were selected randomly. As a result, the neighborhood tanks were inundated and the livelihoods of the poor farmers in those tanks were severely affected. The objective of the study was to identify the cascade system and to assess the tank performance. Kovilkulam Agrarian Centre in Vavuniya was selected for this pilot study. GIS platform was used to identify cascade systems among the tanks in Kovilkulam Agrarian Centre in which 83 tanks were located including abandoned tanks. This study identified 17 tank cascade systems consisting 66 tanks and 17 isolated tanks. Among those 66 tanks, 30 tanks were randomly selected to assess the tank performance. Cropping intensity (CI) and hydrological endowment were used to assess the performance of the tanks. Results revealed that 64% of tanks were with good hydrological endowment whereas 36% were with poor hydrological endowment. Average tank density was one tank per 2.65 km2 in the study area. The average yield under minor tank irrigation systems, good hydrologically endowed tanks and poor hydrologically endowed tanks were 4456 kg/ha (0.44 kg/m2), 5092 kg/ha (0.51 kg/m2) and 3876 kg/ha (0.39 kg/m2) respectively. The average cropping intensity of good and poor hydrologically endowed tanks was statistically tested using t-test and found to be significant. Nearly 90% of the good hydrologically endowed tanks had the CI of greater than one. This study could be extended to the whole district and to the adjacent districts. Documentation of the cascade system would be useful to carry out rehabilitation activities which are essential to improve the tank performance in this district where tanks are the main source of water for irrigation.
