Sustainable Management of Malwathu Oya Cascade-I: Present Status and Future Needs

Abstract

Village tank cascade System is an old age art of irrigation technology presence, especially in North Central dry zone of Sri Lanka. Some of these cascades were already evaluated but most of them are not yet. In Malwathu Oya Cascade-I, no any comprehensive study was carried out yet, therefore this study aimed conduct a comprehensive study of Malwathu Oya cascade-I including demarcation of meso and micro catchments of this cascade, understanding of characteristics and hydrological endowment of the cascade, estimating tank water storage, runoff and irrigation water demand etc. Catchment, water spread and commanding areas of the individual tanks were measured and tank storage, effective runoff to tanks, irrigation water demand and cascade outflow were estimated. With the results, cascade was evaluated for hydrological endowment of the cascade, cascade water surplus and potential water availability. Malwathu Oya cascade-I is a branched type large cascade with the form index of 3.6. The total area of the cascade is 25.88 square kilometers with overall length of 7.1 kilometers. Total water spread area of the tanks and total commanding area of the tanks are 2.57 and 2.81 square kilometers respectively. Tank water supply adequacy showed that, cascade has adequate source of water to cater the irrigation requirement of the command area. All the individual tanks in the cascade except Kudawewa, Palugaswewa and Sattambikulama showed adequate storage capacity. According to the ratio of cascade area to the total tank water surface area of the cascade and ratio of cascade command area to the total tank water surface area, the cascade can be identified as a cascade with good hydrological endowment and stability. According to the cropping intensity of the cascade, cascade can be categorized as a well performing cascade.