ABSTRACT
J.W. GOWING and P.S. MAHEEPALA Centre for Land Use & Water Resources Research, University of Newcastle upon Tyne, UK.
Abstract In most conventional large-scale irrigation systems imperfect matching between water supply and demand is an inescapable fact of life that leads to operational spillages and contributes to low efficiency in use of water unless provision is made for reuse of return flows. Provision of auxiliary storage reservoirs at strategic points within the system can improve the recovery of return flows and absorb surplus supply that would otherwise be wasted. Other benefits also arise including more flexibility of supply within the distribution system and greater opportunity for multiple-use management, including fish production. A method of optimal operation of secondary storage reservoirs has been developed, which employs stochastic dynamic programming within a hierarchical multilevel framework. Application of the method was demonstrated using a case study in Sri Lanka. The proposed method provides higher utilisation of rainfall and lower operational losses than conventional operating methods, regardless of the size of the secondary reservoir. Further work on multiple-use management of systems incorporating such tanks is continuing. Keywords: Irrigation systems, modelling, return flow, secondary storage, water saving.
