A multi-source water allocation method for oasis agricultural irrigation areas with complex canal systems

Abstract

The present invention discloses a method for joint allocation of multiple water sources in oasis agricultural irrigation areas with complex canal systems. The method first simulates the typical annual Longkou water inflow process of abundant, normal, dry and extremely dry years by using a long series of Longkou water intake data based on the P-III frequency analysis method. Then, based on the system coupling principle, the irrigation system engineering distribution and the hydraulic coefficient calculation process are coupled, and the net water demand and gross water demand of each crop in the metering unit are calculated according to the planting plan and the irrigation system. Finally, based on the self-iterative optimization principle, water resources are allocated for each metering unit according to the water balance of the whole process of water demand, the groundwater quality and the water distribution principle, with the goal of minimizing the degree of water demand damage in the whole process. The method has the advantages of strong robustness, easy global convergence and fast calculation speed, and has good fitting effect with the actual water distribution process. The calculation results can be used to guide the scientific water distribution of irrigation area agriculture.

Description

Technical Field

[0001] The present invention relates to multiple technical fields such as water resources engineering, agricultural engineering, hydrology and software engineering, and in particular to a multi-source water allocation method for oasis agricultural irrigation areas with a complex canal system. Background Art

[0002] In agricultural irrigation, particularly in oasis irrigation areas, water distribution within complex canal systems remains a pressing challenge. This issue not only concerns the rational use of water resources but also directly impacts the stability and sustainability of agricultural production. Oasis irrigation areas are typically located in arid or semi-arid regions, where water resources are scarce and unevenly distributed. To fully utilize limited water resources, these areas typically construct complex canal systems that distribute water to individual farmlands through various processes, including water diversion, transmission, and distribution.

[0003] However, due to the influence of various factors such as topography, climate, and crop types, water allocation often presents numerous difficulties. First, water allocation within complex canal systems needs to take into account the irrigation needs of different farmlands. Different crops have different water requirements and irrigation methods, so rational allocation needs to be made based on actual conditions. However, due to limitations in information acquisition and processing, accurate water allocation is often difficult to achieve. Second, water allocation also needs to consider the sustainable use of water resources. In arid areas, the regenerative capacity of water resources is limited, and overexploitation and irrational use are likely to lead to water depletion.

[0004] Taking the large agricultural irrigation area of Shaya County as an example, the actual cultivated land area in Shaya County, as determined by the third survey, was 2.7 million mu. The irrigation area has 1,072 canals at four levels: main, branch, ditch, and agricultural, totaling 2,378.78 km. The drainage canal is 1,620 km long, and there are 2,692 agricultural mechanical and electrical wells. Of these, 1,188 are equipped with IC card metering but not electronic control equipment. The main canal is managed by the Shaya County Water Supply Station, while the main, branch, and some ditch canals are managed by the Xingya Water Company and various township water supply offices. With the demands of economic development, the irrigation area of Shaya County has gradually expanded, and the construction and commissioning of water conservancy facilities have improved the reliability of agricultural irrigation. However, due to the lack of scientific and systematic research on the county's agricultural irrigation system, the irrigation area's management mechanism is incomplete, its methods are outdated, and it lacks necessary monitoring hardware. Irrigation management personnel lack professional expertise and systematic training and education, relying solely on experience to allocate water for irrigation. This lags significantly behind advanced modern irrigation districts, resulting in irrational agricultural irrigation water supply plans and difficulties in implementation. The main problems are as follows: (1) The water supply and water demand situation in each irrigation area is unclear; (2) The agricultural irrigation water supply in each irrigation area relies solely on experience, and a scientific distribution system has not yet been established. Summary of the Invention

[0005] In order to solve the above problems, the present invention proposes a multi-source joint allocation method for oasis agricultural irrigation areas with complex canal systems, which can provide a scientific water allocation plan for the irrigation area and guide the actual water distribution process of the irrigation area.

[0006] To achieve the above purpose, the present invention adopts the following technical solutions:

[0007] A multi-source water allocation method for oasis agricultural irrigation areas with a complex canal system specifically comprises the following steps:

[0008] Step 1: Using the historical data of the water intake and the groundwater availability index of the irrigation area, simulate the typical annual water flow process of different frequencies in the irrigation area. The specific steps include:

[0009] Step 1.1: Use Matlab software to programmatically estimate the P-III distribution parameters using the moment method, solve the design values of water inflow at different frequencies, calculate the empirical frequency of water inflow, and solve the water inflow process in typical years. The specific steps are as follows:

[0010] P-Ⅲ distribution parameter moment method estimation:

[0011] n=length(a) (1)

[0012] p=mean(a) (2)

[0013] m=std(a) (3)

[0014] Cv=m / p (4)

[0015] Cs=sum((ap) 3 ) / ((n-3)*m 3 ) (5)

[0016] A=4 / Cs 2 (6)

[0017] Where: a is the historical water inflow data over the years; n, p, m, Cv, and Cs are the time length, monthly average flow, standard deviation, potential coefficient, and skewness coefficient of the water data over the years, respectively; A is the parameter of the Γ distribution;

[0018] Solve the design value of water coming in at different frequencies:

[0019] tp=gaminv(1-x(i) / 100,A,1) (7)

[0020] Z(i)=((Cs*tp / 2-2 / Cs)*Cv+1)*p (8)

[0021] Where: x(i) is a set frequency; tp is the cumulative probability of the gamma function of x(i); Z(i) is the design value of water coming out of a certain frequency;

[0022] Solving the empirical frequency of incoming water

[0023] pj(i)=n(i) / (n+1) (9)

[0024] Where: n(i) is the length of time greater than a set frequency x(i); pj(i) is the empirical frequency of x(i); solve the water process in a typical year

[0025]

[0026] Where: k is the multiplication coefficient, Q(i) is the empirical value of water flow at a certain frequency;

[0027] Step 1.2: Search the historical data for the annual water withdrawal process that is closest to the design flow rate for different water inflow frequencies: 25% for a wet year, 50% for a normal year, 75% for a dry year, and 95% for a very dry year. The product of this water withdrawal process and k is the typical annual water flow process for different water inflow frequencies. Furthermore, by considering the available water index of groundwater, the typical annual water flow process for different frequencies of multiple water sources in the agricultural irrigation area can be obtained.

[0028] Step 2: Combine the information on canals at all levels, planted area, plot type, and crop type, and calculate the net and gross water requirements of each crop within the control area of each metering unit in the irrigation district based on the irrigation schedule and complex canal system. The specific steps include:

[0029] Step 2.1: Couple the channel information of each metering unit (main trunk, branch, ditch, and farm channel) with the crop type, plot type, and irrigation method under each metering unit. The channel information includes the length of each channel at each metering unit and the anti-seepage status of the channel.

[0030] Step 2.2: Calculate the net water demand process of crops, channel water utilization coefficient, and gross water demand process based on channel information, planting conditions, and irrigation system;

[0031] Calculation of net water demand:

[0032]

[0033] Where: W d净 (i) is the daily net water requirement of crop i; S(i) is the irrigation area of crop i; q(i,l) is the irrigation quota for crop i under the irrigation sequence of crop l; T d (i,l) is the number of irrigation days for crop i under irrigation sequence l;

[0034] According to the above method for calculating daily net water demand, traverse the different irrigation sequences of the crop and sort the calculation results by time to obtain the annual water demand process of the crop on a daily scale. Based on this, the net water demand process of different crops and different measurement units can be obtained.

[0035] Calculation of gross water demand:

[0036]

[0037] Where: η is the water utilization coefficient; σ is the water loss rate per unit length of the channel; L is the channel length;

[0038]

[0039] Where: K is the soil permeability coefficient; m is the soil permeability index; Q dj is the net flow;

[0040]

[0041] Where: W d毛 (i) is the daily gross water requirement of crop i;

[0042] According to the engineering layout of the irrigation system, the gross water demand process of each crop in each metering unit is calculated using formula (12)-formula (13) respectively;

[0043] Step 2.3: Based on the irrigation priority order, use the calculation method in step 2.2 to calculate the net water requirement and gross water requirement of each measurement unit under different irrigation orders;

[0044] Step 3: Based on the water demand balance analysis process at each stage under different water inflow frequencies, with the goal of minimizing the degree of water demand damage during the water distribution process throughout the planting year, surface water and groundwater are jointly allocated based on the self-iterative optimization principle. The water quality of groundwater is taken into account during the water distribution process. The specific steps include:

[0045] Step 3.1: Based on the water inflow process calculated in step 1 and the water demand process of each metering unit calculated in step 2, the water demand process is corrected by feedback, taking into account the water outage period of Longkou water inflow and the selection of water supply time for winter and spring irrigation;

[0046] Step 3.2: Considering only the water inflow process from Longkou, calculate the water shortage degree in each period according to the water demand process calculated in Step 2. Based on the self-iterative optimization principle, allocate the available water index of groundwater according to the water shortage degree and the priority of water distribution, and complete the joint allocation of surface water and groundwater. The optimization goal is to minimize the degree of water demand damage in the whole process, as shown in Equation (15):

[0047]

[0048] Where: R min (i) is the degree of water damage during the entire process of metering unit i; r(i,t) is the degree of water damage during the entire process of metering unit i during period t;

[0049] In the process of water resource allocation, we must follow the water balance constraints in time and space and the water flow capacity constraints of channels, such as Equations (16) and (17):

[0050] W 地表水 (i,t)+W 地下水 (i,t)=W 配水 (i,t)+W 损失 (i,t)+W 余水 (i,t) (16)

[0051] Where: W 地表水 (i,t),W 地下水 (i,t),W 配水 (i,t),W 损失 (i,t),W 余水 (i, t) are the surface water supply, groundwater supply, water distribution, water distribution process loss, and surface water surplus in the water supply period t for the i-th water supply target;

[0052]

[0053] Where: The sum of the L water supply targets Q(i,q,t) flow rates on the qth channel during period t is less than or equal to Q of the qth channel. max (q) Design flow rate;

[0054] In addition to the above-mentioned water balance constraints and channel water capacity constraints, the constraints also include the upper limit of crop water demand, the upper limit of surface water supply, the upper limit of groundwater use, the groundwater quality constraints, and the non-negative water quantity constraint.

[0055] The specific solution steps are as follows:

[0056] (1) When the sum of the monthly water shortage is less than 0, the incoming water can meet the water demand at all times of the year, and the water distribution process is the water demand process;

[0057] (2) When the sum of the water shortages in a month is greater than or equal to 25% of the total water demand, the water shortage is too great and it is suggested to readjust the planting plan;

[0058] (3) When the sum of water shortage in the month is greater than or equal to 0 and less than 25% of the total water demand:

[0059] 1) Divide 25% of the total water demand into five stages, and explore the initial water adjustment amount based on the difference between the total water shortage at different frequencies and the total water demand at different stages;

[0060] 2) Find the period with the greatest water demand destruction in each water distribution period, and then allocate the surplus water with an adjustment step size of 1% of the total water demand. Both the stage and the step size are adjustable parameters. The smaller the step size, the higher the model accuracy.

[0061] 3) Allocate surplus water according to the priority order of crops and land types: priority 1, food crops-secondary land; priority 2, food crops-mobile land; priority 3, cash crops-secondary land; priority 4, cash crops-mobile land;

[0062] 4) Continue to execute 1) to 3) until the remaining water in each time period is distributed;

[0063] 5) The final output is the water distribution process, groundwater distribution process, and the degree of water demand damage in each period.

[0064] Beneficial effects of the present invention:

[0065] (1) Based on the idea of distributed computing, the complex canal system and water utilization coefficient of the irrigation area are layered and graded according to the actual water distribution process and irrigation area characteristics. According to the corresponding relationship between canal projects at all levels and water utilization coefficients, the water demand process of each crop in different measurement units of the irrigation area is calculated;

[0066] (2) Based on the principle of self-iterative optimization, with the goal of minimizing the degree of water demand damage throughout the entire process, and with sustainable development, fairness, efficiency, and water conservation as the priority of water allocation, surface water and groundwater are jointly allocated according to the water demand throughout the entire process. The allocation process also takes into account the groundwater quality (water quality is a limiting condition);

[0067] (3) The present invention quantifies the scientific water distribution process of the irrigation area based on the actual situation of the irrigation area. This model is integrated into the modern irrigation area platform of Shaya County. Through continuous mutual verification with the measured data, it can eventually construct a scientific water distribution system for the local agricultural irrigation area in Shaya County. BRIEF DESCRIPTION OF THE DRAWINGS

[0068] Figure 1 This is a schematic diagram of the research area of the present invention.

[0069] Figure 2 This is a schematic diagram of the distribution of township nodes in the main canal area of the present invention.

[0070] Figure 3 A schematic flow chart of a multi-source water allocation method for oasis agricultural irrigation areas with a complex canal system.

[0071] Figure 4 Flowchart of the self-iterative optimization simulation water allocation algorithm.

[0072] Figure 5 This is the spatial variation relationship of water utilization coefficients of channels at all levels in 9 townships in the irrigation area of this invention.

[0073] Figure 6 This is a comparison between the actual water distribution and simulated water distribution processes in the irrigation area of the present invention.

[0074] Figure 7 The actual water volume allocated to each township in the irrigation area of this invention is compared with the water volume simulated by the model.

[0075] Figure 8 The results of model water demand simulation and water allocation optimization in different typical years are shown.

[0076] Figure 9 It is the linear fitting relationship between annual water volume and annual water allocation.

[0077] Figure 10 This is an example of the groundwater and surface water usage process in the irrigation area during a dry year.

[0078] Figure 11 This is an example of the groundwater and surface water usage process of Gate No. 4 in a dry year.

[0079] Figure 12 This is an example of the groundwater and surface water usage process in a certain measurement unit in a dry year.

[0080] Figure 13 An example of groundwater and surface water use processes for a certain measurement unit taking into account groundwater quality in a dry year. DETAILED DESCRIPTION

[0081] The technical solutions of the present invention will be described clearly and completely below with reference to the accompanying drawings.

[0082] like Figure 1 As shown in the figure, the irrigation system in the study area of this invention consists of main canals, main canals, branch canals, ditches, agricultural canals, and field plots, among which thousands of wells are scattered. Figure 2 As shown, in addition to considering the project layout, the actual local water distribution process also needs to be considered. That is, after water is taken from Longkou, it reaches 390 metering units in 9 townships through 27 water diversion points. In the case of water shortage, groundwater is used for regulation and replenishment. The irrigation system of the entire irrigation area is very complicated.

[0083] like Figure 3 As shown, in view of the above complex situation, the present invention proposes a multi-source joint allocation method for oasis agricultural irrigation areas taking into account the complex canal system, including the following steps:

[0084] Step 1: Based on the P-III frequency analysis commonly used in my country's hydrological frequency, the design values of different water inflow frequencies are solved. The same-multiple amplification method is used to calculate the monthly Longkou water intake process in different typical years. This is the available surface water volume. The specific calculation formula is as follows:

[0085] P-Ⅲ distribution parameter moment method estimation:

[0086] n=length(a) (1)

[0087] p=mean(a) (2)

[0088] m=std(a) (3)

[0089] Cv=m / p (4)

[0090] Cs=sum((ap) 3 ) / ((n-3)*m 3 ) (5)

[0091] A=4 / Cs 2 (6)

[0092] Where: a is the historical water inflow data over the years; n, p, m, Cv, and Cs are the time length, monthly average flow, standard deviation, potential coefficient, and skewness coefficient of the water data over the years, respectively; A is the parameter of the Γ distribution;

[0093] Solve the design value for different water inflow frequencies:

[0094] tp=gaminv(1-x(i) / 100,A,1) (7)

[0095] Z(i)=((Cs*tp / 2-2 / Cs)*Cv+1)*p (8)

[0096] Where: x(i) is a certain set frequency; tp is the cumulative probability of the gamma function of x(i); Z(i) is the design value under a certain inflow frequency;

[0097] Solving the empirical frequency of incoming water

[0098] pj(i)=n(i) / (n+1) (9)

[0099] Where: n(i) is the length of time greater than a certain set frequency x(i); pj(i) is the empirical frequency of x(i);

[0100] Solve the water process in typical years

[0101]

[0102] Where: k is the multiplication coefficient, Q(i) is the empirical value under a certain water inflow frequency;

[0103] In the historical water inflow data over many years, we search for the water inflow process that is closest to the design flow rate for different water inflow frequencies: wet year (25%), normal year (50%), dry year (75%), and extremely dry year (95%). The product of this process and k is the typical annual water inflow process under different water inflow frequencies. In addition, considering the available water index of groundwater, we can obtain the available water process of multiple water sources in agricultural irrigation areas.

[0104] Step 2: Calculate crop water requirements in the irrigation area, including net and gross water requirements. Specific steps include:

[0105] Calculation of net water demand:

[0106] The calculation of net water demand is determined by the planting area and irrigation system of different crop types. The calculation program sequentially reads the pure groundwater irrigation area in the database and the crop type, planting area and irrigation start time, irrigation duration and irrigation quota of the corresponding crop in the planting structure summary table. The daily net water demand process of a certain crop is calculated by formula (11). The water demand process calculation of different crops in a year adopts an assumption that the daily irrigation water supply is the same within a certain irrigation cycle of a certain crop.

[0107]

[0108] Where: W d (i) is the daily net water requirement of crop i; S(i) is the irrigation area of crop i; q(i,l) is the irrigation quota for crop i under the irrigation sequence of crop l; T d (i,l) is the number of irrigation days for crop i under irrigation sequence l;

[0109] According to the above method for calculating daily net water demand, traverse the different irrigation sequences of the crop and sort the calculation results by time to obtain the annual water demand process of the crop on a daily scale. Based on this, the net water demand process of different crops and different measurement units can be obtained.

[0110] Calculation of gross water demand:

[0111] Based on the calculation of the net water demand of the metering unit and the canal layout of the irrigation area, the Shaya County irrigation area is divided into Longkou-27 water diversion points / 9 townships-390 metering units. The water utilization coefficient is divided into the main trunk-main trunk-branch-ditch-farm-field water utilization coefficient. The two are calculated separately according to the temporal and spatial relationship. The calculation is based on the "Irrigation and Drainage Engineering Design Standard" (GB50288-2018). The specific calculation formula is as follows:

[0112]

[0113] Where: σ is the water loss rate per unit length of the channel; L is the channel length;

[0114]

[0115] Where: K is the soil permeability coefficient; m is the soil permeability index; Q dj is the net flow;

[0116] Considering the large cross-section and wide water surface of the canal, as well as the dry climate, low precipitation, and intense evaporation at the project site, groundwater extracted from drought-resistant wells is used to irrigate each metering unit through the canal system. Taking these factors into account, a water loss rate of approximately 1% was considered based on the theoretically calculated value. Based on the calculated canal water utilization, the water utilization coefficient was calculated using the coefficient multiplication method. From this, the gross water requirement for each crop and metering unit, excluding spring irrigation, was determined based on the calculated net water requirement.

[0117] Step 3: Based on the calculation of water inflow and water demand, the supply and demand balance in each time period is calculated, and the irrigation system of the crops is reselected according to the most unfavorable principle to perform a second calculation of the crop water demand; then, based on the water shortage and available groundwater in each time period, starting from the water demand process of all crops in the entire irrigation area, the available water resources are optimized based on the self-iterative optimization principle.

[0118] Optimization goal:

[0119] Water resources are allocated to each metering unit to maximize the use of surface water and groundwater. Groundwater is used as a regulating water source. The entire irrigation cycle is analyzed, and the period with the greatest water shortage is continuously identified for supplementary irrigation until the groundwater consumption reaches the upper limit. Ultimately, the goal of minimizing surplus water and water demand damage throughout the entire irrigation cycle is achieved, while ensuring fair and reasonable water resource allocation. As shown in Equation 15, the damage in each period is minimized, and the damage throughout the entire irrigation cycle is minimized.

[0120]

[0121] Where: R min is the degree of water destruction required for the entire process of metering unit i; r min (i,t) is the degree of water damage of the metering unit during period i;

[0122] Constraints:

[0123] In the process of water resource allocation, we must follow the water balance constraints in time and space and the water flow capacity constraints of channels, as shown in Equations 15 and 16:

[0124] W 地表水 (i,t)+W 地下水 (i,t)=W 配水 (i,t)+W 损失 (i,t)+W 余水 (i,t) (15)

[0125] Where: W 地表水 (i,t),W 地下水 (i,t),W 配水 (i,t),W 损失 (i,t),W 余水 (i, t) are the surface water supply, groundwater supply, water distribution, water distribution process loss, and surface water surplus in the water supply period t for the i-th water supply target;

[0126]

[0127] Where: The sum of the L water supply targets Q(i,q,t) flow rates on the qth channel during period t is less than or equal to Q of the qth channel. max (q) Design flow rate;

[0128] In addition, the constraints also need to consider crop water demand, surface water supply, groundwater water use ceiling indicators, and groundwater quality;

[0129] Solution:

[0130] like Figure 4 As shown in the figure, after preprocessing the inflow and demand calculation results, a balance calculation is performed for water inflow and demand at different frequencies. First, an overall calculation indicator is given: the total annual water shortage, which is the sum of the monthly water shortage and the annual available groundwater volume. Second, five 5% damage intervals and a 1% search step are specified. The degree of damage to irrigation water demand for different crops in different metering units can be determined by using the damage interval, search step, and the water allocation priority order for different crops and plot types.

[0131] The specific solution steps are as follows:

[0132] (1) When the sum of the monthly water shortage is less than 0, the incoming water can meet the water demand at all times of the year, and the water distribution process is the water demand process;

[0133] (2) When the sum of the water shortage in the month is greater than or equal to 25% of the total water demand, the water shortage is too large and a prompt is given to “re-adjust the planting plan”;

[0134] (3) When the sum of water shortage in the month is greater than or equal to 0 and less than 25% of the total water demand:

[0135] 1) Divide 25% of the total water demand into five stages, and explore the initial water adjustment amount based on the difference between the total water shortage at different frequencies and the total water demand at different stages;

[0136] 2) Find the period with the greatest water demand destruction in each water distribution period, and then allocate the remaining water with an adjustment step size of 1% of the total water demand (both the stage and the step size are adjustable parameters; the smaller the step size, the higher the model accuracy);

[0137] 3) Allocate surplus water in order of priority of crops and plot types (priority 1, food crops-secondary land; priority 2, food crops-mobile land; priority 3, cash crops-secondary land; priority 4, cash crops-mobile land);

[0138] 4) Continue to execute 1) to 3) until the remaining water in each time period is distributed;

[0139] 5) The final output is the water distribution process, groundwater distribution process, and the degree of water demand damage in each period.

[0140] The present invention simulates the water flow processes in four typical years of abundant (25%), normal (50%), dry (75%), and extremely dry (95%) in the Weigan River Irrigation District of Shaya County based on the Longkou water inflow data and groundwater availability indicators from 2002 to 2021. The calculation method refers to step 1, and the calculation results are shown in Tables 1 and 2.

[0141] Table 1 Monthly water extraction process at Longkou of Weigan River at different frequencies

[0142]

[0143] Table 2 Annual available water volume in the Weigan River irrigation area of Shaya County

[0144]

[0145] The net water demand of the irrigation area is calculated based on the planting plan for 2022, the local irrigation system and the layout of the canal engineering project. The calculation method refers to step 2. Among them, the calculation of the channel water utilization coefficient takes into account factors such as the anti-seepage capacity of channels at all levels, the spatial distance between each metering unit and the water intake, and evaporation. According to the above factors, each parameter is explained separately: the soil type in Shaya County is light loam with medium-strong permeability. The soil permeability coefficient K and the soil permeability index m are selected as 2.65 and 0.45 respectively; the net flow of the ditch, branch canal, main canal and main canal is based on the average net flow of representative channels in the "Shaya County Planning Report", which are 0.75m3 / s and 1.50m 3 / s、5.95m 3 / s、44.00m 3 / s; the anti-seepage coefficient of the anti-seepage lining of branch canals, main canals and main trunk canals is 0.20, and the anti-seepage coefficient of the anti-seepage lining of ditch canals is 0.35; considering the differences in channel anti-seepage, channel length, channel net flow, as well as the possibility of evaporation, water leakage and other factors, correction coefficients of the water utilization coefficients of each level of channels are set, and their values are between 0.00-0.10. Under the above parameter settings, the calculated average values of the channel water utilization coefficients of ditch canals, branch canals, main canals and main trunk canals are 0.92, 0.90, 0.87 and 0.86 respectively, and the average value of the channel water utilization coefficient is 0.70. Figure 2 Schematic diagram of the distribution of township nodes of the main canal in the implementation area, such as Figure 5 As shown in the figure, the water utilization coefficient, channel water utilization coefficient and water utilization coefficient of canal systems at all levels spatially conform to the trend that the utilization coefficient value gradually decreases as the distance from Longkou increases.

[0146] like Figure 6 and Figure 7 As shown, the actual water distribution process in 2022, the actual water distribution process in 2023, and the simulated water demand process under the 2022 planting plan show essentially identical trends, indicating that the planting structures and irrigation schedules for the three are essentially the same, thus proving the rationality of the water demand calculation method of this invention. The correlation coefficients between the actual water distribution process in 2022 and 2023 and the simulated water demand process in 2022 are 0.77 and 0.74, respectively. According to the survey, because the simulated water demand calculation uses the crop planting plan calculated at the beginning of the year, it is 2%-3% higher than the actual planted area. After accounting for area deviation, the correlation coefficient between the actual water distribution process and the simulated water demand process can reach above 0.87, indicating good simulation accuracy of the model.

[0147] The actual water use process in the towns and villages of the Weigan River irrigation area and the gross water demand calculation of the model have a good temporal and spatial connection, and the two verify each other, which proves the reliability of the measured data and the reliability of the gross water demand calculation of the present invention.

[0148] The actual annual water demand of the Weigan River irrigation area is 980 million m 3 The present invention simulates water allocation based on the water conditions in different typical years. The calculated results are 844 million m3 in the flood year and 844 million m3 in the wet year. 3 , 829 million m3 in normal water year 3 , 776 million m3 in dry years 3 , 745 million m3 in a particularly dry year 3 , water demand process and water distribution process are as follows Figure 8 As shown in the figure, during the entire irrigation year, the main water shortage periods are October-November, April-May, and June-August. When surface water cannot meet the demand, limited groundwater is used for supplemental irrigation. The specific principle is to select the most severe water shortage period within all water shortage periods and replenish water according to the spatial extent of the damage and water allocation priority.

[0149] The water inflow process at Longkou of Weigan River, the surface water surplus process, the groundwater use process, and the reserved mobile water process in different typical years are shown in Tables 3, 4, 5 and 6.

[0150] Table 3 Water inflow process in Longkou in different typical years

[0151]

[0152] Table 4 Groundwater consumption process in different typical years

[0153]

[0154] Table 5 Surface water residual process in different typical years

[0155]

[0156] Table 6 Reserved maneuverable water process in different typical years

[0157]

[0158] In the case of abundant water in the years with abundant water, the surface residual water generated by the imbalance of water inflow is 82 million m3. 3 , groundwater use reached the upper limit of 81 million m 3 (groundwater usage index 200 million m 3 , pure well irrigation area 119 million m 3 ), the degree of water demand disruption was 12.68%. The degree of disruption to water demand in normal, dry, and extremely dry years was 15.23%, 19.95%, and 24.55%, respectively (the disruptions here are maximum values and do not account for approximately 40 million m³ of unused water). The processes of Longkou water inflow, groundwater use, surface water surplus, reserved unused water, and distributed water conform to a water balance, demonstrating the reliability of the calculations presented in this invention.

[0159] By comparing the simulated values with the actual values under different water inflow conditions and analyzing the water supply and demand balance under different water inflow conditions, it can be concluded that the present invention has good reliability.

[0160] like Figure 9 As shown in the figure, each point represents a water allocation scheme, and a linear fit is performed based on the water allocation scheme. When the water inflow and water demand are known, the water allocation scheme and water allocation effect at the full scale of ten days, month and year can be obtained. Taking the annual scale as an example, when the water inflow is 760 million m 3 The degree of damage of this water distribution scheme is about 19.95%. When the water inflow changes, according to the fitting relationship, the changes in the annual water distribution process can be clearly obtained. By corresponding it to the crop yield under this scheme, the changing relationship between water supply and yield can be obtained.

[0161] The present invention can also provide a more detailed water supply process, such as Figure 10 、 Figure 11 、 Figure 12 and Figure 13 As shown, they represent the surface water and groundwater use process lines of the irrigation area water intake, 27 water diversion outlets, 390 metering units, and the groundwater quality metering unit.

[0162] The calculation method of this invention is a progressive optimization adjustment based on actual past process data. Model parameters are corrected using measured data, and model parameters can be optimized at three stages: one, three, and five years after the model is put into operation. Initial model parameters can be quickly corrected using one year of data, and higher-precision model parameters can be obtained using three and five years of historical data.

[0163] The above-described embodiments merely represent specific implementations of the present invention. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make various modifications and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the appended claims.

Claims

1. A method for joint allocation of multiple water sources in oasis agricultural irrigation areas with complex canal systems, characterized in that: The specific steps include: Step 1: Using the historical data of the water intake and the groundwater availability index of the irrigation area, simulate the typical annual water flow process of different frequencies in the irrigation area. The specific steps include: Step 1.1: Use Matlab software to programmatically estimate the P-III distribution parameters using the moment method, solve the design values of water inflow at different frequencies, calculate the empirical frequency of water inflow, and solve the water inflow process in typical years. The specific steps are as follows: P-Ⅲ distribution parameter moment method estimation: （1） （2） （3） （4） （5） （6） Where: It is the historical water data for many years; 、 、 、 、 They are the time length, monthly average flow, standard deviation, potential coefficient, and skewness coefficient of water data over the years. for Parameters of the distribution; Solve the design value of water coming in at different frequencies: （7） （8） Where: Set the frequency for a certain for cumulative probability of the gamma function; Design value of water coming in at a certain frequency; Solving the empirical frequency of incoming water （9） Where: is greater than a certain set frequency the length of time; for The empirical frequency of Solve the water process in typical years （10） Where: is the ratio coefficient, is the empirical value of water flow at a certain frequency; Step 1.2: Search the historical data for the annual water withdrawal process that is closest to the design flow rate with different water inflow frequencies of 25% in a wet year, 50% in a normal year, 75% in a dry year, and 95% in an extremely dry year. The product of is the typical annual water flow process under different water inflow frequencies. In addition, considering the available water index of groundwater, the typical annual water flow process of different frequencies of multiple water sources in agricultural irrigation areas can be obtained. Step 2: Combine the information on canals at all levels, planted area, plot type, and crop type, and calculate the net and gross water requirements of each crop within the control area of each metering unit in the irrigation district based on the irrigation schedule and complex canal system. The specific steps include: Step 2.1: Couple the channel information of each metering unit (main trunk, branch, ditch, and farm channel) with the crop type, plot type, and irrigation method under each metering unit. The channel information includes the length of each channel at each metering unit and the anti-seepage status of the channel. Step 2.2: Calculate the net water demand process of crops, channel water utilization coefficient, and gross water demand process based on channel information, planting conditions, and irrigation system; Calculation of net water demand: （11） Where: for Net daily water requirement of crops; for Irrigated area of crops; for crop Watering quota under the watering sequence; for crop Number of irrigation days under the irrigation sequence; According to the above method for calculating daily net water demand, traverse the different irrigation sequences of the crop and sort the calculation results by time to obtain the annual water demand process of the crop on a daily scale. Based on this, the net water demand process of different crops and different measurement units can be obtained. Calculation of gross water demand: （12） Where: is the water utilization coefficient; is the water loss rate per unit length of the channel; is the channel length; （13） Where: is the soil permeability coefficient; is the soil water permeability index; is the net flow; （14） Where: for Gross daily water requirement of crops; According to the engineering layout of the irrigation system, the gross water demand process of each crop in each metering unit is calculated using equations (12) and (13). Step 2.3: Based on the irrigation priority order, use the calculation method in step 2.2 to calculate the net water requirement and gross water requirement of each measurement unit under different irrigation orders; Step 3: Based on the water demand balance analysis process at each stage under different water inflow frequencies, with the goal of minimizing the degree of water demand damage during the water distribution process throughout the planting year, surface water and groundwater are jointly allocated based on the self-iterative optimization principle. The water quality of groundwater is taken into account during the water distribution process. The specific steps include: Step 3.1: Based on the water inflow process calculated in step 1 and the water demand process of each metering unit calculated in step 2, the water demand process is corrected by feedback, taking into account the water outage period of Longkou water inflow and the selection of water supply time for winter and spring irrigation; Step 3.2: Considering only the water inflow process from Longkou, calculate the water shortage degree in each period according to the water demand process calculated in step 2. Based on the self-iterative optimization principle, allocate the available water index of groundwater according to the water shortage degree and the priority order of water distribution, and complete the joint allocation of surface water and groundwater. The optimization goal is to minimize the degree of water demand damage in the whole process, as shown in formula (15): （15） Where: for The degree of water destruction required during the whole process of the metering unit; for Time Degree of water damage required for metering unit; In the process of water resource allocation, we must follow the water balance constraints in time and space and the water flow capacity constraints of channels, such as Equations (16) and (17): （16） Where: 、 、 、 、 Respectively Water supply target Surface water supply, groundwater supply, water distribution, water loss during distribution, and surface water surplus during the water supply period; （17） In the formula: On the channel Time water supply targets The sum of the flow is less than or equal to Channel Design flow rate; In addition to the above-mentioned water balance constraints and channel water capacity constraints, the constraints also include the upper limit of crop water demand, the upper limit of surface water supply, the upper limit of groundwater use, the groundwater quality constraints, and the non-negative water quantity constraint. The specific solution steps are as follows: (1) When the sum of the monthly water shortage is less than 0, the incoming water can meet the water demand at all times of the year, and the water distribution process is the water demand process; (2) When the sum of the water shortage in a month is greater than or equal to 25% of the total water demand, the water shortage is too large, prompting a readjustment of the planting plan; (3) When the sum of water shortage in the month is greater than or equal to 0 and less than 25% of the total water demand: 1) Divide 25% of the total water demand into five stages, and explore the initial water adjustment amount based on the difference between the total water shortage at different frequencies and the total water demand at different stages; 2) Find the period with the greatest water demand damage in each water distribution period, and then allocate the surplus water with an adjustment step size of 1% of the total water demand. Both the stage and step size are adjustable parameters. The smaller the step size, the higher the model accuracy. 3) Allocate surplus water according to the priority order of crops and land types: priority 1, food crops-secondary land; priority 2, food crops-mobile land; priority 3, cash crops-secondary land; priority 4, cash crops-mobile land; 4) Continue to execute 1) to 3) until all remaining water in each time period is distributed; 5) Final output of water distribution process, groundwater distribution process, and degree of water demand damage in each period.

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