河网区灌溉水利用系数的尺度转换

摘要

大尺度灌区灌溉水利用系数的测定条件难以保障，而小尺度灌区的灌溉水利用系数可以通过试验测定，如何通过小尺度灌区的灌溉水利用系数来预测大尺度灌区的灌溉水利用系数，就有必要对灌溉水利用系数的尺度转换问题进行研究。河网灌区的特点是没有统一的水源引水口，通常是由若干个小灌区合并成一个大灌区，是一个典型的自相似系统。论文以地处里下河水网地区的盐城市水稻灌区作为研究对象，于2012－2013年对9个县区不同规模的样点灌区进行了灌溉水利用系数的试验观测，利用分形理论研究了河网灌区的分形特征，运用盒维数法计算了盐城市河网灌区和不同尺度灌区的盒维数，其盒维数介于1.703～1.996之间，并随着面积尺度的增加而增大。基于灌溉水利用系数与灌区面积、盒维数的相关性，建立了河网灌区灌溉水利用系数尺度转换模型，并通过验证，表明该尺度转换模型能够较好地预测河网灌区灌溉水利用系数，同时也能够很好地实现灌溉水利用系数的尺度转换，为分析河网灌区灌溉水利用系数及其尺度效应提供了新途径。%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.