Analysis of efficiency of water utilization in canal-system in Hetao irrigation district based on Horton fractal

Efficiency of water utilization in large irrigation districts and water-saving potential can reflect degree of water resources utilization and is an important evaluation index of national economic development. It is unknown about effects of canal-system framework on water utilization efficiency in canal-system. In this study, we assessed the relationship between canal-system framework and water utilization efficiency in Hetao Irrigation District, China. The Hetao Irrigation District was divided into Wulanbuhe, Jiefangzha, Yongji, Yichang, and Wulate sub-irrigation districts. The canal-system of Hetao Irrigation district had complex structure with one general canal, 16 trunk canals, 48 sub-main canals, and 57 000 of branch, lateral, field, and sublateral canals. The general, trunk, sub-main, branch, lateral, field and sublateral canals were graded into the first, second, …, and seventh levels. The information on irrigation area, amount, and water use efficiency of each sub-irrigation district in 2012 was collected. Canal-system framework was described by Horton law. The fractal dimension of canal system was calculated based on branch ratio and length ratio of canals. Relationships between fractal dimensions, irrigation amount, efficiencies of water utilization, and irrigation area were evaluated. Then, the proportion of water-saving was calculated. The results showed that the logarithms of canal numbers and length had good linear relationships with canal levels (R2>0.9), indicating the estimation of fractal dimensions was highly reliable. Fractal dimensions in sub-irrigation districts of Hetao Irrigation District were 1.14 for Wulanbuhe, 1.86 for Jiefangzha, 2.21 for Yongji, 1.80 for Yichang, 1.99 for Wulate and 1.88 for Hetao. The fractal dimensions were similar for all sub-irrigation districts because the branch and length ratios were similar. In general, branch ratio of canal-systems was too high in Hetao Irrigation District and should be reduced. The relationship among efficiency of water utilization in canal-system, fractal dimension, planting area and irrigation amount was in quadratic function. Based on these relationships, a multivariate quadratic function was fitted with small residues and relative errors smaller than 0.8%. The potential of canal-systems to increase water use efficiencies was 19.01% for Wulanbuhe, 28.80% for Jiefangzha, 32.70% for Yongji, 27.07% for Yichang, and 30.70% for Wulate. It also estimated that the canal-system water-saving development speed averaged 27.19% in Hetao Irrigation District, which was smaller than 28.06% achieved by lining method when lining rate is assumed to be 100% reported by previous studies. However, both lining method and structure optimization method were reliable methods for canal-system plan in irrigation district. Therefore, it is viable to apply Horton Law to canal-system in large irrigation districts. The results here provide valuble information for planning and water-saving reconstruction of irrigation districts. ©, 2015, Chinese Society of Agricultural Engineering. All right reserved.