Modelling and multicriteria analysis of water saving scenarios for an irrigation district in the upper Yellow River Basin

Abstract

Water saving in irrigation is a main issue in the Yellow River basin. This paper refers to a field and modelling study performed in the Huinong Irrigation District, a very large surface irrigation system in Ningxia, upper Yellow River basin, intended to assess water saving and improved water use issues. The decision support system SEDAM was purposefully developed to evaluate alternative scenarios of improvements of farm and off-farm irrigation canal systems. It includes a demand and delivery simulation tool and adopts multicriteria analysis. Simulation is performed at various scales, starting at the distributor and then successively at the sub-branch, branch and sector scales. It uses a database built from random generation of system characteristics at these scales, and based on field surveys. Demand is built from exploring interactively the irrigation scheduling simulation model ISAREG and the surface irrigation models SRFR and SIRMOD, which were previously parameterized. The first is used to generate improved irrigation schedules and the second to define improved basin irrigation scenarios. In addition, a simple paddy irrigation tool is used to simulate replacing the current deep flooding method by shallow water irrigation. Water delivery scenarios are built to match those of demand including several improved procedures that aim at controlling runoff and seepage. Results indicate that progressively adopting farm and delivery system improvements leads to reduced canal seepage and runoff, which is essential to an effective functioning of the drainage system, in addition to control diversions into the Huinong canal. Water savings amount to more than 50% of actual water use. However, results referring to the economic criteria, particularly to the farm gross margin, reveal that more stringent improvements have low impacts, i.e. the respective utilities increase little when scenarios require higher investments. The described application shows that adopting a DSS simulation model and multicriteria analysis is appropriate to assess water use improvements in large irrigation systems and that it is advantageous to perform the analysis of related impacts by combining economic and environmental criteria. The importance of adopting improved delivery systems is also evidenced.