| Heilongjiang Province is an important grain producing area and commodity grain export base in China.It not only guarantees the daily consumption of nearly 1.4 billion people in China,but also makes great contributions to the food-scarce countries in the world.However,the shortage of water resources is a thorny problem facing our country.With the rapid development of all walks of life,the proportion of water resources is increasing year by year,so the amount of water available in agriculture is becoming less and less.Comprehensive analysis of relevant data shows that the irrigation water use efficiency of Heilongjiang Province has been ranked in the middle and lower level in the country for many years.To some extent,the advantages and disadvantages of the fractal characteristics of the irrigation area can reflect the rationality of the canal system layout,optimize the fractal structure of the canal system and reduce redundant channels appropriately,which can effectively reduce the waste of agricultural water caused by leakage and evaporation loss of the canal.Irrigation water use efficiency is mainly used to evaluate the status of agricultural irrigation water in an irrigation area.It can also reflect the status of irrigation projects,the level of irrigation water management and the popularization of water-saving irrigation technology in an irrigation area.Comprehensive and reasonable evaluation of irrigation water use efficiency in Heilongjiang Province can lay a scientific theoretical foundation for the planning and development of water-saving technology in the area.According to statistics,there are 20 large-scale irrigation districts,305 medium-sized irrigation districts and 9136 small-scale irrigation districts in Heilongjiang Province at the present stage.However,due to the differ ences in geographical location and management mode of each irrigation district,the development of irrigation water use efficiency in different scales and types of irrigation districts in Heilongjiang Province is not balanced,and the gap between them is gradually increasing.In this study,20 typical sample irrigation districts of different types and scales in Heilongjiang Province were selected to study the canal system structure and fractal characteristics,spatial and temporal distribution characteristics and driving mechanism of irrigation water use efficiency in these irrigation districts,and find out the rational canal system layout and the main factors affecting the irrigation water use efficiency.It is very necessary to steadily improve the irrigation water use efficiency in Heilongjiang Province.Based on the field investigation of typical irrigation districts in Heilongjiang Province,this study classifies irrigation districts;studies the canal system structure and fractal characteristics of different irrigation districts using Horton law;explores the spatial and temporal distribution characteristics of irrigation water use efficiency in typical irrigation districts;analyses the driving mechanism of irrigation water use efficiency;the main research contents and results are as follows:(1)The canal system structure and fractal characteristics of 10 typical irrigation districts of three and four-level in Heilongjiang Province were studied by Horton’s law.The results showed that the canal system structure of Woken River and Xingkai Lake irrigation districts in three-level typical irrigation districts was complex,and the canal system structure of the irrigation districts of Tintang,Jixian,Tuogu and Cangliang was relatively simple;the canal system structure of Chahayang and Hamatong irrigation districts in four-level typical irrigation districts was simple.The canal system structure of Wutong River,Dongfanghong,Hongqi and Zhaonong irrigation districts is relatively simple;the two indexes of canal system structure complexity and canal density can reflect the complexity of canal system structure in irrigation districts;the canal system structure of irrigation districts has similarity,and the fractal dimension values of three and four-level irrigation districts are basically within the scope of general regulations.The canal system distribution of typical irrigation districts in Heilongjiang Province is similar.It conforms to the self-organizing and optimizing structure of nature.(2)The time-varying characteristics of irrigation water use efficiency of typical irrigation districts in Heilongjiang Province from 2010 to 2014 and the spatial distribution characteristics of irrigation water use efficiency in 2014 were analyzed respectively.The results showed that the irrigation water use efficiency of irrigation districts ranged from 0.300 to 0.700,and the irrigation water use efficiency of small and medium-sized irrigation districts in three-level irrigation districts > the irrigation water use efficiency of large-scale irrigation districts > the irrigation water use efficiency of medium-sized irrigation districts.Irrigation water use efficiency in the middle-sized irrigation area is higher than that in the large-scale irrigation area in the fourth-level irrigation districts.The spatial distribution characteristics of irrigation water use efficiency in 2014 are Zhaonong irrigation districts in the west of Heilongjiang Province,Dongfanghong irrigation districts in the south,Yintang irrigation districts in the middle and Hongqi irrigation districts in the southeast.The irrigation water use efficiency in Songnen Plain and Sanjiang Plain in the northeast is the largest.The average value of irrigation water use efficiency is larger in the irrigation districts,while the irrigation water use efficiency in the irrigation districts with mountainous and hilly topography is relatively small.(3)The driving mechanism of influencing factors of irrigation water use efficiency in typical irrigation districts of Heilongjiang Province was studied by using grey relational analysis method and least squares curve fitting theory.The results showed that the irrigation water use efficiency in the plain area was higher than that in the hilly area when the level of irrigation districts was the same and the topographic conditions were different.When the topographic facies of irrigation districts was different,the irrigation water use efficiency in the plain area was higher than that in the hilly area.At the same level,the higher the grade of irrigation districts,the higher the irrigation water use efficiency;when the soil type of irrigation districts is loam,the higher the irrigation water use efficiency;there are some redundant channels in the existing chan nel system of the three and four-level typical irrigation districts,which have low function in the process of water transmission and distribution,resulting in low irrigation water use efficiency;in the three-level irrigation districts,the channel density and irrigation water use efficiency are low.The correlation degree is the largest,0.700,and the correlation degree between canal structure complexity and fractal dimension is the largest,0.711.In the four-level irrigation districts,the ratio of water-saving irrigation area and irrigation water use efficiency is the largest,0.730,and the correlation degree between effective irrigation area and fractal dimension value is the largest,0.763.The rationality of canal system structure is the key facto r affecting the function of water transfer and distribution in the three-level irrigation districts,and the perfect water-saving measures are the important factors to improve the efficiency of irrigation water use in the fourth-level irrigation districts.(4)Based on the four scenarios in which the effective irrigation area,the proportion of water-saving irrigation area and fractal dimension are considered comprehensively and one of them is considered separately,the "causal analysis method" is used to p redict the irrigation water use efficiency of Heilongjiang Province in 2020 and 2025.The results show that the improvement value of the irrigation water use efficiency predicted by considering three factors at the same time is smaller than that by considering one factor alone.It is easier to improve the efficiency of irrigation water use in a short time and reach the target value of the 13 th Five-Year Plan and the 2025 forecast. |
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