Demand Irrigation Schedule Pilot Project: Sri Lanka

Since 1981, the Sri Lanka Government has been testing a different approach to delivering irrigation water to its numerous small‐scale farmers. Instead of conventional open‐channel rotation irrigation with water controlled by government organizations, a 367‐acre (147‐ha) pilot project has put each farmer in control of his own water supply using a limited‐rate demand irrigation schedule. This system conjunctively utilizes sloping canals, on‐stream regulating reservoirs, automatic float‐controlled canal gates, level‐top canals, and buried concrete pipelines with float valves to maintain low pressure. Discussed are construction costs and materials, the four cropping seasons evaluated, and the advantages and disadvantages compared to conventional irrigation. Current data show that: an adequate and equitable water supply can be achieved and sustained; crop production can be increased from 8 to 20 bushels/acre (160 to 400 kg/ha); the potential exists for reducing water use below that of conventional irrigation; and that farmer contention is nearly eliminated. Project cost was about 5,860 rupees/acre [$325/acre ($810/ha)] compared to 3,350 rupees/acre [$185/acre (465/ha)] for the conventional system. The resulting incremental increased cost is about 75% at the distributary channel level but about only 7–10% of total project development costs.