Planning of modern irrigation systems integrated with human settlement for enhanced reuse of water

Abstract

There are five independent development areas situated in the dry zone of Sri Lanka each consisting of irrigation systems which are similar in principle, but substantially different as far as the design concept and the operations are concerned. These systems are to receive surface water in the corresponding basins plus diverted waters of the largest river in Sri Lanka, for socio-economic development. The five systems presently in operation following settlement of farmer-families and non-farmer families, are H, C, B, G, and L. The irrigation and drainage network in each system demonstrates a planning concept, which is a combination of minor reservoirs, irrigation canals and drainages, towards optimization of irrigation system efficiency. The principle incorporated into the planning concept is therefore the "Cascade of minor reservoirs" constructed across the secondary and tertiary drainages to command the farm area below. This concept which was adopted several centuries ago, is still in existence in the dry zone. In some of the major integrated rural development projects, the minor reservoirs have been incorporated into the irrigation and drainage system to provide a number of purposes, benefiting the human settlements and their environments. Another beneficial function of these reservoirs, when combined with the canals and drainages is its versatility in fitting into the irrigation and drainage network at any location. The quality of irrigation water has still not been a serious problem in any of the areas described above. However, it has been recognized that there should be field research into the quality of water, from the planning stage to operation & maintenance. The social benefits, both direct and indirect, are concerned collection and distribution of return flows, by means of Canal-Reservoir integration have produced a successful concept, in integrated rural development based on human settlement and irrigated agriculture.