Scale transformation of utilization coefficient of irrigation water in riverine irrigation district

Abstract: Utilization coefficient of irrigation water is a key indicator to measure agricultural water-saving efficiency, and it reflects comprehensively the level of water management and irrigation technology and so on.Obtaining reliable data of the utilization coefficient of irrigation water by direct in situ determination methods is difficult in large irrigation districts, but it can be determined by field experiments in the small-scale area. Hence, one of the challenges is to conduct researches on scale transformation in order to predict the utilization coefficient of irrigation water at large-scale irrigation district by the measured utilization coefficient of irrigation water at small irrigation district. The main characteristic of irrigation districts in riverine area is that there is no unified water diversion, and several small irrigation districts usually merge into a larger one. The area is a typical self-similar system. The existence and reusing of the agricultural returning water have induced much debates about the real water-saving potential of the irrigation districts in riverine area, and also the scale effect of utilization coefficient of irrigation water. The paper selected the rice irrigation districts of Yancheng City in Lixiahe riverine region as the experimental object. The study area is flat, where the river and ditch network are densely distributed. Totally, 4 large-scale irrigation districts, 11 medium-scale and 32 small-scale irrigation districts were selected to measure and calculate the utilization coefficient of irrigation water by inclusive method. The utilization coefficients of irrigation water in sampling irrigation districts with different scales were measured in 9 counties in 2012-2013. Fractal characteristics of these riverine irrigation districts were analyzed based on fractal theory. In addition, box dimensions of the Yancheng riverine area and the irrigation districts with different scales were respectively calculated by box-counting method. The box dimension ranged from 1.703 to 1.966, and increased with the increasing of irrigation district area scale. The scale transformation model of utilization coefficient of irrigation water was established based on the relationships among utilization coefficient of irrigation water, irrigation area and box dimension. The calibration results verified that the scale transformation model could predict the utilization coefficient of irrigation water in the riverine irrigation district with high prediction accuracy. With the developed model, the scale transformation of utilization coefficient of irrigation water was performed successfully. This study provides a new way to analyze the utilization coefficients of irrigation water and their transformation in different scales in riverine irrigation districts. In the future, if the means of geographic information system (GIS) is used in calculating the box dimensions, the accuracy of the research will be further improved.