Research On Evaluation And Allocation Of Effective Utilization Of Water Resource At Different Scales In Well-canal Combined Irrigated District

As agricultural water use efficiency is very low, and water waste is serious and the contradictions between water supply and demand are also very prominent, water resources have become a major factor restricting agricultural development in China. The well-canal combined irrigated district will play an increasingly important role in agricultural production, and the significance of studying efficient use of water resources in the well-canal combined irrigated area to alleviate China’s agricultural water crisis is outstanding. Furthermore, it is necessary to carry out a research on the evaluation and deployment of efficient utilization of water resources at different scales in well-canal combined irrigated district. It takes a very special significance in correctly understanding the real connotation of efficient utilization of agriculture water resources, changing the traditional mode of agricultural water development, and constructing water-saving and efficient agriculture, etc.This paper defines the real connotation of efficient utilization of water resources in well-canal combined irrigated district. Surrounding it and based on the water balance method of International Water Management Institute (IWMI), an analysis method about researching the scale effects of effective utilization of water resources in well-canal combined irrigated district has been proposed. Taking the People’s Victory Canal Irrigation District as a case study, the scale effect and evolutionary law of the evaluation index system of efficient utilization of water resources under the condition of well-canal combined models in different level years have been studied. On this basis, a comprehensive evaluation index system for efficient utilization of water resources at different scales in well-canal combined irrigated district is constructed. Then a soil water-salt united dynamic optimal allocation model combining the irrigation district scale with the field scale in well-canal combined irrigated district is established. Finally, both of them are applied in the People’s Victory Canal Irrigation District. The main research results are as follows:(1) The concept and system combination of well-canal combined irrigated district have been anatomized, and its main types and engineering arrangement forms have been inducted and concluded, furthermore the function of its efficient utilization of water resources has been analyzed. Then, in the perspective of the essence of sustainable development and sustainable utilization of resources, the concept and characteristics of efficient utilization of water resources and efficient utilization of water resources in irrigation district have been clarified, and the mechanism of efficient utilization of water resources in the well-canal combined irrigated district has been revealed. Lastly, the connotation of efficient utilization of water resources in well-canal combined irrigated district has been clearly defined.(2) Based on water balance method of IWMI, considering the actual situation that the groundwater should be recycled to use and the input-output effect between canal irrigation and well irrigation can be different, the analysis indicators of irrigation return water and irrigation benefit-cost are proposed to take as the scale-effect research analysis indicators of efficient utilization of water resources in well-canal combined irrigated district. This has expanded the applicability of water balance method of IWMI. Finally, an analysis method suitable for the scale-effect research of efficient utilization of water resources in well-canal combined irrigated district is presented.(3) Aiming at the disadvantages of SWAT model, which take little account of the characteristics of the plain irrigation district and the module of dry crops, this paper has amended some calculation modules, such as capillary soil water, groundwater depth, canal seepage, evapo-transpiration, and a dry-crop simulation module. Furthermore, they are all coupled with MODFLOW software to construct a distributed coupling simulation model of groundwater and surface water. Lastly, the model is calibrated and verified with the data of the actual measured runoff, evapo-transpiration and groundwater level from the People’s Victory Canal Irrigation District, and the results show that the created model can be used to simulate water balance elements of different scales in the plain well-canal combined irrigated district.(4) Taking the People’s Victory Canal Irrigation District as a case study, through setting different irrigation situation models and dividing the study area into 4 kinds of scales:field, branch canal, sub-main canal and the whole irrigation district, the created model is applied to simulate the water balance elements in different scales of the irrigation district in order to research the variations of the analysis indicators,such as water productivity, irrigation return water and irrigation benefit-cost, etc, with the scales. The results show that:the analysis indicator of return water is better at the irrigation district scale than at the other scales; the analysis indicator of water productivity and benefit-cost at the field scale are the best; water use is higher efficiency in normal year than in dry year; but when comparing and selecting irrigation modes, the different conclusions are also drawn based on different indicators. Therefore, the more comprehensive indicators been considered, the more accurate conclusion can be achieved.(5) According to the connotation of efficient utilization of water resources in well-canal combined irrigated district, considering the scale effects of evaluation index, based on the field scale evaluation and focusing on the irrigation district scale evaluation, a comprehensive evaluation index system is established at field or irrigation district scale, respectively. Here, the field scale indexes fall into 3 categories of water use efficiency, economic benefit and environment benefit, with a total number of 6. Additionally, in the irrigation district scale, it includes 4 categories and 11 indicators classified as water utilization efficiency, economic benefit, social benefit and environment benefit. Based on this, a multi-level fuzzy comprehensive evaluation model is established.(6) After distinguishing relationship between allocation model and evaluation indexes, a surface water and groundwater joint optimal allocation model and a soil water-salt dynamic optimal allocation model are established, respectively. The former belongs to irrigation district scale, and is mainly based on the water production function, while the latter belongs to field scale, and is mainly based on the water-salt production function, and the concept of critical soil salt content, critical groundwater mineralization degree and critical groundwater level is introduced. In order to balance the benefit of different management subject in each scale, the two models are coupled to create a large system decomposition coordination optimization model of soil water-salt combined dynamic optimal allocation in well-canal combined irrigated district; in the mean time, the solving method of each model and the operation process of coupling model are given. The results show that the built model can achieve the multi-scale and multi-dimension water-salt regulation of well-canal combined irrigated district.(7) Taking the year of 2010 as current year, research on the comprehensive evaluation and allocation of efficient utilization of water resources at different scales is applied into the People’s Victory Canal Irrigation District. The results show that both the built comprehensive evaluation index system and model are workable, and it can be a valid decision reference for efficient utilization of water resources at different scales. Moreover, the built optimal allocation model is reasonable, and it can be applied to regulate the evaluation indexes of efficient utilization of water resources. And then, taking the year of 2020 as planning year, based on the different water resources allocation approach, through setting 7 allocation schemes of water resources in irrigation district, both the comprehensive evaluation index system at irrigation district scale and the fuzzy comprehensive evaluation model are applied to achieve the best allocation scheme of water resources in the planning year.