Study On Water Demand And Utilization Process In Jinghui Irrigation District

Statistical analysis of annual data was conducted for water diversion from head and water use of irrigation. Annual rainfall was considered as well as actual planting structure and irrigation system, actual water habit of farmers, water use coefficient of channel at all levels in irrigation district.Then theoretical irrigation water demand and practical irrigation water diversion as well as water use process. Water demand process, actual water supply process and water demand of actual irrigation system in irrigation district were analyzed, The main contents were as follows:(1) Penman—Monteith equation was used to calculate reference crop evapotranspiration from 1993 to 2000. Principal component analysis of each factor was done which affecting reference crop evapotranspiration and determined new factors according to their contribution. ET₀ which was predicted by BP neural network model and multiple linear regression model was compared with that calculated by Penman—Monteith equation. It indicated that the maximum error and the average relative error of prediction by multiple linear regression model were 31.50 percent and 11.66 percent, but the value by BP neural network model were only 21.30 percent and 7.81 percent. Therefore, the accuracy of BP neural network model was higher than that of multiple linear regression model and BP neural network model could be used to predicted ET₀.(2)Typical years were determined by analyzing weather of representative site and frequency of rainfall data. The comparasion of reference crop evapotranspiration among typical sites eventually confirmed jingyang site used to determine the basic data of crop water requirement. Month-by-month crop coefficients of the whole main corp growth period were ascertained by comparing single crop coefficient, dual crop coefficient as well as the actual situation. Crop water demand was also confirmed each month in the whole growth period, which of winter wheat was 299.49 milimeters to 348.69 milimeters, summer maize 410.55 milimeters to 559.09 milimeters, and cotton 583.82 milimeters to 745.04 milimeters. Furthermore, water requirement regulation and extreme value of water requirement intensity were ascertained by analyzing crop water requirement process of different hydrological years, which of winter wheat was 2.75 milimeters per day to 3.02 milimeters per day, summer maize 5.01 milimeters per day to 5.86 milimeters per day and cotton 5.31 milimeters per day to 6.21 milimeters per day. (3)The data of actual water segrating of canal system and water distribution were utilized as well as practical irrigation quota to determine water efficiency of irrigation, which also was confirmed by terminal method. The result indicated that water efficiency of irrigation varied from 0.503 to 0.598 and average annual water efficiency of irrigation was 0.548. The fluctuaion of coefficient was not serious and the fluctuation between the minimum limit and the upper bound was equivalent. It proved that the management level was high in the irrigation district and operation of canal system was good. GM (1,1) grey forcasting model was used to predict irrigation water use efficiency from 2009 to 2013, which ranged from 0.561～0.572.(4)Water balance equation was adopted to determine the theoretical total irrigation water requirement which varied 3.22×10⁸m³ to 4.68×10⁸m³,which of winter wheat was about 0.68×10⁸m³ to 1.44×10⁸m³ ,summer maize 1.07×10⁸m³ to 2.16×10⁸m³ ,cotton 0.13×108m³ to 0.26×10⁸m³and others 0.91×10⁸m³ to 1.39×10⁸m³. If the actual situation was considered, the total water requirement varied from 2.08×10⁸m³ to 3.07×10⁸m³ and the average annual water requirement was about 2.67×10⁸m³.The cannal and well both were used in the irrigation district.Then,well irrigation and groundwater supply were considered.Therefore, the net water requirement of channel irrigation ranged from 1.15×10⁸m³ to 1.70×10⁸m³ and the average annual total water demand of it was 1.49×10⁸m³.(5)The comparasion between water diversion required and actual water diversion during the year from 1993 to 2001 showed that the difference between them was not large. Water deficit merely occurred in the dry year and arid year, however, water kept balanced in other hydrological years—rainy years and medium years.The maximum water deficit appeared in 2000(P=90%,dry year) and the amount of water deficit was 4.38×10⁷m³. In the year, irrigation requirement rate was only 0.739.(6) It indicated that there existed large difference between them by comparing water requirement process and water use process. Water requirement rised from March, but there was no significant increase in water diversion, on the contrary, showing the downward trend. It was two reasons that led to the phenomen. Firstly, diversion discharge of head was influenced by such factors as inflows of water source and silt content of river, and practical water distribution process and water requirement process didn't completely coincide. Secondly, water diversion staggering the peak was conducted, in other words, water diversion increased and water was imported to regulating reservoir when water was in great demand. Water was in great demand after March or April, when inflows decreased and silt content of river rised. It maked water intake keep low in the stage, sometimes, water diversion was forced to cease. (7) The analysis of the current irrigation system ascertained water requirement curve of different hydrological years according to the irrigation system. Water diversion of head needed was between 9.081 m³/s～10.90 m³/s in winter. It increased gradually in winter and spring, reaching the maximum 52.58 m³/s in summer. Compared with the actual water diversion curve, the current irrigation system basically satisfied water use in the rainy years and water requirement in other hydrological years (medimum years, arid years) in winter and spring. However, the difference of them both in summer increased as the degree of aridity rised. The irrigation district belonged to the area of water defict. The measures were taken that deficit irrigation was conducted combined with canal irrigation and well irrigation. Then the irrigation system basicall satisfied water use in the irrigation district and the i irrigation district run well.