Evaluation On Performance Of A Large-scale Irrigation System

In China, the middle and large-scale irrigation system play an important role in food production. Due to ageing and poor management, these systems have low irrigation efficiency and a large potential for water savings. Therefore, an extensive rehabilitation and modernization of the irrigation systems has being carried out for increasing water use efficiency. This paper takes the Bojili irrigation district as an example to evaluate irrigation performance of the systems, to define the water losses and analyze underlying causes as a basis to rehabilitate and modernize the irrigation system. In order to adapt to conditions of the system, the evaluation methods have been selected and modified and new field test methods and procedures have been developed. In Boj iii Irrigation District, three levels .of irrigation water management can be distinguished: 1) the main system managed by the irrigation agency; 2) the farm system managed by a township irrigation station and a group of farmers; 3) the field system managed by the individual farmers. For the main system (main canals), the mean discharge model and the integral model have been developed based on Kostiakov equation. The model validation and the parameters calibration have been done with historical discharge records, and then water use efficiency of the main system has been estimated with both models. For the farm level (Lateral, tertiary and farm ditch), an evaluation procedure has been developed. Firstly, a typical canal was selected to measure the seepage losses with several experimental methods. Secondly, the seepage process was analyzed with the selected theoretical model to determine the saturated permeability of the canal bedding soil and the withstanding coefficient of the ground water table underlying the canal bed. Finally, the farm system was typified according to soils and section configurations of canals to generate the relations between the water use efficiency and the discharge at different types of canals. For the field system, according to the measured data in field irrigation experiment the irrigation process was simulated using the SRFR model, and the soil parameters were determined by inverse method .The field system was typified according to the soil types and basin size, and the water efficiency of all types was determined by simulating. Then the relation between the intake rate and the application efficiency was analyzed, the most suitable intake rate and application time for all types were defined.