An assessment system, method, and storage medium for the migration process of winter irrigation water in farmland.

Abstract

This invention discloses an evaluation system, method, and storage medium for the winter irrigation water transport process in farmland, comprising the following steps: Step 1: Selection of study area, study time, and verification area; Step 2: Analysis of the winter irrigation water transport path in the study area, divided into four levels: "irrigation canal - farmland surface - farmland groundwater - drainage ditch," constructing a water transport system; Step 3: Construction of an irrigation canal water transport algorithm; Step 4: Construction of a farmland surface water transport algorithm; Step 5: Construction of a farmland groundwater transport algorithm; Step 6: Construction of a drainage ditch water transport algorithm. Using the method and system of this invention, reasonable irrigation and drainage improvement methods can be proposed through simulation and prediction of irrigation and drainage volume and time. Predictions were made in the Ningxia section of the Yellow River Basin, with the overall 34-day winter irrigation period remaining unchanged, but delayed by 1 to 8 days for water saving predictions. Prediction results show that delaying winter irrigation can effectively improve the water transmission efficiency in the irrigation canal.

Description

Technical Field

[0001] This invention belongs to the field of agricultural water-saving technology, specifically an evaluation system, method and storage medium for the migration process of winter irrigation water in farmland. By simulating and predicting irrigation and drainage volume and time, reasonable methods for improving irrigation and drainage are proposed. Background Technology

[0002] Against the backdrop of global water scarcity, water conservation in agriculture is seen as a key challenge. It is commonly believed that strictly controlling agricultural water use can improve water efficiency. However, this reliance solely on reducing water consumption not only alters water transport processes but also wastes canal resources, neglecting the necessity of adjusting management strategies after changes in water transport paths. Winter irrigation is a crucial agricultural practice for maintaining soil moisture in farmland, relying on water transport process assessment methods to determine irrigation amounts. Under the combined influence of water-saving measures and global warming, the soil freezing rate during winter irrigation has decreased, making it difficult to achieve the ideal goals of salinization and moisture retention. Pre-water-saving winter irrigation water transport process assessment methods focused on water transport within the canal system, easily meeting groundwater content thresholds. However, post-water-saving winter irrigation prioritizes meeting groundwater content thresholds before utilizing the canal system for water transport. Overall, the assessment method for the winter irrigation water transport process before water conservation has two problems when applied after water conservation: 1) inaccurate assessment results lead to a serious reduction in winter irrigation water quotas; 2) it is difficult to achieve a reasonable assessment of winter irrigation water. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide an evaluation system, method and storage medium for the migration process of winter irrigation water in farmland, which addresses the shortcomings of the prior art.

[0004] The technical solution of the present invention is as follows:

[0005] A method for assessing the migration process of winter irrigation water in farmland includes the following steps:

[0006] Step 1: Selection of research area, research time, and validation area;

[0007] Step 2: Analyze the winter irrigation water transport path in the study area, dividing it into four levels: "water diversion canal - farmland surface - farmland underground - drainage ditch", and construct a water transport system;

[0008] Step 3: Construct a water transport algorithm for the irrigation canal;

[0009] Step 4: Construct an algorithm for farmland surface water transport;

[0010] Step 5: Construct an algorithm for farmland groundwater transport;

[0011] Step 6: Construct a drainage ditch water transport algorithm.

[0012] The method described in step 2, which analyzes the winter irrigation water transport path in the study area, includes the following steps: analyzing the water transport path of the irrigation canal; analyzing the surface water transport path of farmland; analyzing the groundwater transport path of farmland; analyzing the water transport path of the drainage ditch; constructing the water transport system; and constructing a complete winter irrigation water transport system based on the analyzed structure.

[0013] The method described above, in step 2, involves analyzing the migration path of winter irrigation water in the study area, including the following steps:

[0014] Analysis of the water transport path of the diversion canal: Water is diverted from the Yellow River (WDI) to the diversion canal (Cn), and after evaporation loss (ECn) and human loss (WU), it is diverted to farmland for irrigation (WF);

[0015] Analysis of the surface water transport path in the farmland: Irrigation (WF) and rainfall (P) water reach the farmland, and after evaporation (EF) and pumped irrigation (PI), the water infiltrates into groundwater (PSA), with some water replenishing the surface (RSA). The farmland water content before irrigation is Wsa, and the farmland water content after irrigation is Wsb.

[0016] Analysis of the farmland groundwater migration path: Surface water infiltrates into the farmland groundwater (PSA), then flows through irrigation ditches (IS1), surface recharge (RSA), and pumped irrigation (PI), before flowing into drainage ditches (RFDi) and the Yellow River (RFD0). The groundwater level before irrigation is Wua, and the groundwater level after irrigation is Wub.

[0017] Analysis of the water transport path in the drainage ditch: After the groundwater flows to the drainage ditch (RFDi) (Dn), it undergoes evaporation loss (EDn) and flows into the Yellow River (WDR).

[0018] The method described in step 3, which involves constructing a water transport algorithm for the diversion channel, includes: constructing a water balance algorithm for the diversion channel; constructing a water evaporation algorithm; constructing a water vapor pressure algorithm; and constructing a 40-minute scale algorithm.

[0019] The method described above, in step 3, specifically includes constructing the water transport algorithm for the irrigation canal:

[0020] The water balance algorithm for the irrigation canal is constructed as follows: the irrigation canal draws water from the river, and after passing through n stages of irrigation canals, it reaches the farmland; the algorithm for drawing water from the river to the farmland is as follows:

[0021] WF = WDI-EC n -WU=C n -WU

[0022] Wherein, WF is the amount of water delivered to the fields; WDI is the amount of water diverted from the river; EC is the evaporation from the irrigation canal; n represents different levels of irrigation canals, 1, 2, 3, ..., n; WU is the amount of unused water that has not been used for farmland; and C is the amount of water retained in different levels of irrigation canals.

[0023] The water evaporation algorithm is constructed as described above; water evaporation is calculated using Dalton's theorem, modified for suitability of the study area.

[0024]

[0025] Where E is the saturated vapor pressure at the water surface temperature, which is 3170 Pa at 25℃; e150 is the actual vapor pressure at a height of 150 cm above the water surface; u 150 The sum of wind speed (u1) and current velocity (u2) at a depth of 150 cm above the water surface is expressed in m / s.

[0026] The water vapor pressure algorithm described above is constructed as follows:

[0027] 1) Calculation of saturated water vapor pressure:

[0028]

[0029] Where t is in degrees Celsius;

[0030] 2) Calculation of actual water vapor pressure:

[0031] e = Ef

[0032] Where f is the relative humidity; relative humidity directly reflects the degree to which the air is not saturated; when f = 100%, the air is saturated; when it is unsaturated, f < 100%; when it is supersaturated, f > 100%; the magnitude of relative humidity is not only related to the water vapor content in the atmosphere, but also decreases as the temperature rises; when the water vapor pressure remains constant, as the temperature rises, the saturated water vapor pressure increases, and the relative humidity decreases.

[0033] The 40-minute scale algorithm is constructed as follows: Due to the influence of Earth's rotation, the evaporation trend, primarily affected by temperature, exhibits a periodic fluctuation as a cosine function; the cosine function is introduced to calculate water evaporation on a 40-minute scale; the simplified formula is as follows:

[0034]

[0035] Where EC is the instantaneous evaporation rate; c0 is the average evaporation rate, which is controlled by the average temperature; A is the water evaporation amplitude, which is controlled by the minimum and maximum temperatures; c is the radial frequency of water evaporation; and t is the unit time on a 40-minute scale. The lag time for water evaporation in response to temperature; the simulation time is from 10:00 AM to 10:00 AM the next day, with 40 minutes as the basic calculation unit.

[0036] The method described in step 4 includes constructing the farmland surface water transport algorithm, which includes: constructing the water balance algorithm for irrigation canals; constructing the PSA algorithm for surface water infiltration into groundwater; constructing the farmland evapotranspiration (EF) algorithm; and constructing the RSA algorithm for groundwater replenishment to the farmland surface.

[0037] The method described above, in step 4, specifically involves constructing the farmland surface water transport algorithm as follows:

[0038] The water balance algorithm for the irrigation canal is constructed as follows: water first enters the surface layer of farmland (T); the dynamic balance formula for the surface layer of farmland is:

[0039] PSA = P + WF - EF + RSA + W sa -W sb

[0040] The aforementioned surface water infiltration into groundwater PSA algorithm is constructed as follows: when the water content of a certain layer exceeds its field capacity and the underlying layer is unsaturated, water will infiltrate; when the soil layer is frozen, no water flows out from the soil layer. The permeable water volume in the soil layer can be calculated using the following formula:

[0041] SW ly,ex =SW ly -FC ly

[0042] Among them, SW ly,ex SW represents the permeable water volume of a soil layer on a certain day, in mm. ly This indicates the soil moisture content on a given day, expressed in mm; FC ly The field water holding capacity of the soil layer is expressed in mm; the amount of water that infiltrates from the upper layer to the lower layer is calculated using the storage calculus method.

[0043] The calculation equation is as follows:

[0044]

[0045] Among them, w pere,ly Δt represents the amount of water that seeps into the lower soil layer on a certain day, in mm; Δt represents the time step, in h; TT pere The infiltration time is expressed in hours (h). The infiltration time varies for each layer and is calculated using the following formula:

[0046]

[0047] Among them, SAT ly FC represents the saturated water content of the soil layer, in mm. ly Indicates the field water holding capacity of the soil layer, mm; K sat This represents the saturated permeability coefficient of the layer, in mm / h;

[0048] The aforementioned farmland evapotranspiration (EF) algorithm construction;

[0049] Total farmland inflow - seepage = evaporation = water surface evaporation + soil evaporation (40 min):

[0050] When the total water diversion volume exceeds 100% soil moisture content, the water surface evaporation procedure shall be executed;

[0051] When the total water diversion is less than or equal to 100% soil moisture content, or when the total water diversion minus evaporation minus infiltration is less than or equal to 100% soil moisture content, the soil evaporation procedure shall be executed.

[0052] When the total water intake or water content is greater than or equal to the maximum field capacity, the evaporation rate is equal to Esoil,ly.

[0053] When the total water intake or water content is less than the maximum field capacity, the evaporation rate is calculated as Esoil,ly * exp[2.5(water content - field capacity) / (field capacity - wilting water content)]; the wilting water content during winter irrigation is 0.

[0054] The aforementioned groundwater layer water recharge algorithm for farmland surface (RSA) is constructed;

[0055] RSA (revap) only occurs when the water storage in the shallow aquifer exceeds a user-defined threshold; the maximum amount of water that can migrate from the aquifer via RSA on a given day is:

[0056] w revap,mx =β rev ×E0

[0057] Among them, w revap,mx The maximum amount of water entering the soil zone due to insufficient soil moisture is represented in mm; βrev represents the revap system; E0 represents the potential evapotranspiration on a certain day in mm; the actual revap amount on a certain day is:

[0058]

[0059] w revap =w revap,mx -aq shthr,rvp aq shthr,rvp <aq sh <(aq) shthr,rvp +w revap m,x )

[0060] w revap =w revap,mx q sh ≥(aq shthr,rvp +w revap,mx )

[0061] Among them, w revap This indicates the actual amount of water entering the soil zone due to insufficient soil moisture, expressed in mm; wrevap,mx Represents the maximum amount of water entering the soil zone due to insufficient soil moisture, in mm; aq sh Represents the initial water storage in the shallow aquifer on the i-th day, in mm; aq shthr,rvp Represents the water level threshold in the shallow aquifer when revap occurs, in mm.

[0062] For the method described above, in step 5, constructing the farmland groundwater migration algorithm includes:

[0063] Establish the dynamic balance formula for the farmland underground layer as:

[0064] RFD i =PSA - RSA - PI + IS i -W ua +W ub

[0065] The calculation method of groundwater recharge to the river channel and drainage ditch takes the hydraulic gradient as the core, uses Darcy's law to describe the seepage relationship between river water and groundwater, and calculates the total recharge along the river channel through an integral formula;

[0066] Construction of the hydraulic gradient algorithm for the river channel, drainage ditch and groundwater;

[0067] The main driving force for groundwater recharge to the river channel and drainage ditch is the hydraulic gradient between river water and groundwater, defined as:

[0068] ΔH = hr - hg

[0069] Where, ΔH is the hydraulic gradient; hr is the river water level height; hg is the groundwater level height; when hr > hg, river water recharges groundwater; when hr < hg, groundwater recharges the river channel;

[0070] Construction of the seepage relationship algorithm between river water and groundwater; The seepage between river water and groundwater is described by Darcy's law:

[0071] Q = KsA×ΔH / d

[0072] Where, Q is the seepage flow rate, the amount of water passing through a unit area per unit time, m 3 / s; Ks is the permeability coefficient of the riverbed sediment, m / s; A is the seepage area, m 2 ; ΔH is the hydraulic gradient; d is the thickness of the riverbed sediment, m.

[0073] Construction of the algorithm for river channel and drainage ditch to recharge groundwater; In large-scale studies, the total amount of groundwater recharge by the river channel and drainage ditch is calculated by the following formula:

[0074]

[0075] Where, G is the total recharge amount (m3 / s); L is the river channel length (m); B(x) is a function of the riverbed width, which varies with x; hr(x) and hg(x) are the distributions of river water level and groundwater level with river channel length, respectively;

[0076] River evapotranspiration affects algorithm construction; when calculating groundwater recharge channels, the impact of river evapotranspiration must be considered; evapotranspiration can be calculated using empirical formulas.

[0077] E = α × P × exp(-β × d)

[0078] Where E is the evapotranspiration rate (m³) 3 / s); β is an empirical coefficient; P is the potential evapotranspiration;

[0079] A dynamic change algorithm for groundwater recharge is constructed. Under unsteady conditions, the dynamic changes of the groundwater recharge channel can be described by the following continuity equation:

[0080]

[0081] Where S is the storage capacity of the river channel and groundwater system; Qin is the inflow into the river channel; and Qout is the outflow from the river channel. The calculation of groundwater recharge into the river channel typically involves numerical simulation, using the finite element method to solve the governing equations.

[0082]

[0083] Where h is the head, m; K is the permeability tensor; and R is the source-sink term.

[0084] Water infiltrates into groundwater from the drainage ditch (ISi); the value of i is generally 1. From the agricultural canal to the agricultural ditch, water infiltrates into groundwater from the agricultural ditch; the PSA algorithm is used.

[0085] Water infiltrates into groundwater from the drainage ditch (RFDi); a value of i is 0, indicating that the groundwater directly enters the Yellow River; values ​​of i are 1, 2, 3…, indicating that the groundwater enters the drainage ditch due to the water potential difference; the formula for calculating RFDi is:

[0086] RFD i =S×(d1+d2)×h / 2

[0087] Where S is the length of the ditch (m); d1 and d2 are the upper and lower bottoms of the drainage ditch (m); h is the height (m); the inner slope ratio is 1:2, and the groundwater volume conversion formula is as follows:

[0088] RFD i =S×(d2+Wub-hi)×(Wub-hi) / 2

[0089] Where Wub is the groundwater volume (m) after irrigation; hi is the groundwater level difference before and after irrigation.

[0090] The method described above, in step 6, includes constructing a drainage ditch water transport algorithm, which includes:

[0091] Water conveyance capacity algorithm construction; Manning's formula is used to describe the water flow velocity v and flow rate Q in the drainage ditch:

[0092]

[0093] Q = v × A

[0094] Where v is the flow velocity (m / s); n is the Manning roughness coefficient; Rh is the hydraulic radius (m), defined as the wetted cross-sectional area A divided by the wetted perimeter P; S is the ditch slope; A is the wetted cross-sectional area (m²). 2 );

[0095] Leakage rate algorithm construction; leakage at the bottom of the drainage ditch can be described by Darcy's law:

[0096]

[0097] Where q is the seepage rate per unit area (m / s); Ks is the soil permeability coefficient at the bottom of the ditch (m / s); H is the hydraulic gradient between the water depth and the groundwater level; and d is the thickness of the soil at the bottom of the ditch.

[0098] A dynamic water balance algorithm for drainage ditches is constructed; the dynamic changes in water volume within the drainage ditches satisfy the water continuity equation.

[0099]

[0100] Where V is the water volume in the drainage ditch; Qin is the amount of water entering the drainage ditch; Qout is the amount of water flowing out of the drainage ditch; L is the leakage loss; and E is the evaporation loss.

[0101] Water wave propagation algorithm construction; under dynamic conditions, water transport within the drainage ditch can be described by the Saint-Venant equation:

[0102]

[0103]

[0104] Where h is the water depth; Q is the flow rate; A is the wetted cross-sectional area; g is the gravitational acceleration; and n is the Manning roughness coefficient.

[0105] Canal water enters agricultural ditch (WU); options include whether to allow water to enter the agricultural ditch and the percentage of water entering the agricultural ditch; calculation formula:

[0106] WF(10 8 m 3)=C4×i.

[0107] The selection principles for the study area, study time, and verification area in step 1 of the method include the following: the completeness of the irrigation and drainage system; the representativeness of the study time; the typicality of the verification area; and the feasibility of technical and data support.

[0108] An evaluation system for the migration process of winter irrigation water in farmland includes: a processor and a memory for storing a computer program that can run on the processor; wherein, when the processor runs the computer program, it performs the steps of any of the methods described above.

[0109] A storage medium having a computer program stored thereon, characterized in that the computer program, when executed by a processor, implements the steps of any of the methods.

[0110] A computer program product includes a computer program, characterized in that, when the computer program is executed by a processor, it implements the steps of any one of the methods.

[0111] Compared with existing technologies, it has the following beneficial effects:

[0112] The assessment of water transport processes during winter irrigation after water conservation is more accurate. This invention constructs a water transport system and algorithm framework based on an algorithm for constructing water transport processes after water conservation during winter irrigation, consisting of "water diversion canal - farmland surface - farmland subsurface - drainage ditch". It was applied in the Ningxia section of the Yellow River Basin. During the winter irrigation season of 2020-2023, three main ditches flowing into the Yellow River were selected for monitoring: the Fifth Drainage Ditch, the Middle Main Ditch, and the Luojia River. 411 sets of data were collected over four years for validation. The validation results showed that R... 2 The accuracy is 0.72, NSE is 0.67, RMSE is 0.10, and Pbias is 7.04%, indicating reliable accuracy.

[0113] Achieving reasonable prediction of winter irrigation water is crucial. Through simulation and prediction of irrigation and drainage volume and timing, reasonable methods for improving irrigation and drainage are proposed. With delayed timing, evaporation significantly decreases. Predictions were conducted in the Ningxia section of the Yellow River Basin, where the overall 34-day winter irrigation period remained unchanged, but water savings were predicted by delaying it by 1 to 8 days. Prediction results show that delaying winter irrigation can effectively improve water transmission efficiency in the irrigation canals. Delaying winter irrigation by 1 day saves 5.32 liters of water during the winter irrigation period in the study area. 6 m 3 The water allocation per hectare of farmland increased by 18m. 3 The water diversion efficiency increased by 1.6%; the water saving during the winter irrigation period in the study area was 42.47 cubic meters per second due to the 8-day extension of irrigation. 6 m 3 The water allocation per hectare of farmland increased by 143m³ 3The water diversion efficiency increased by 12.8%. At the same time, the soil freezing rate increased due to the decrease in temperature, which can improve soil moisture in the second year. Attached Figure Description

[0114] Figure 1 A diagram illustrating the water transport process after water-saving winter irrigation in farmland; Detailed Implementation

[0115] The present invention will be described in detail below with reference to specific embodiments.

[0116] Step 1: Selection of study area, study time, and validation area. The selection principles are as follows:

[0117] 1.1 The completeness of the irrigation and drainage system. The study area should be selected from regions with well-developed irrigation and drainage facilities to ensure sufficient water infrastructure to support the monitoring of winter irrigation water transport processes;

[0118] 1.2 Representativeness of the study period. The selected study period should cover different climatic and hydrological conditions in order to obtain data on the variation of water transport processes under different weather and soil conditions;

[0119] 1.3 Typicality of the Verification Area. The selected verification area should be representative and able to reflect the characteristics of water transport under different land use types, soil types, and crop planting methods;

[0120] 1.4 Feasibility of Technical and Data Support: When selecting a study area, it is essential to ensure that there is already sufficient technical support and data foundation, such as the availability of relevant hydrological, meteorological, and soil characteristic data. Simultaneously, the study area should possess suitable conditions for installing monitoring equipment and conducting long-term data tracking, facilitating the implementation of an efficient data acquisition and monitoring system and ensuring the reliability and comparability of the data.

[0121] Step 2: Analyze the winter irrigation water transport path in the study area, which is divided into four levels: "water diversion canal - farmland surface - farmland underground - drainage ditch", and construct a water transport system.

[0122] 2.1 Analysis of water transport path in the irrigation canal. Water from the Yellow River (WDI) is diverted to the irrigation canal (Cn), and after evaporation loss (ECn) and human-caused loss (WU), it is diverted to farmland for irrigation (WF).

[0123] 2.2 Analysis of surface water transport pathways in farmland. Irrigation (WF) and rainfall (P) water reach the farmland, and after evaporation (EF) and pumped irrigation (PI), the water infiltrates into groundwater (PSA), with some water replenishing the surface (RSA). The water content of the farmland before irrigation is Wsa, and the water content of the farmland after irrigation is Wsb.

[0124] 2.3 Analysis of the migration path of farmland groundwater. Surface water infiltrates into the farmland groundwater (PSA), then flows through irrigation ditches (IS1), surface recharge (RSA), and pumped irrigation (PI), before flowing into drainage ditches (RFDi) and the Yellow River (RFD0). The groundwater level before irrigation is Wua, and the groundwater level after irrigation is Wub.

[0125] 2.4 Analysis of water transport path in drainage ditch. After groundwater flows to the drainage ditch (RFDi) (Dn), it undergoes evaporation loss (EDn) and flows into the Yellow River (WDR);

[0126] 2.5 Construction of the water transport system. Based on the structures analyzed in steps 2.1 to 2.4, construct a complete winter irrigation water transport system (such as...). Figure 1 ).

[0127] Step 3: Construct a water transport algorithm for the irrigation canal.

[0128] 3.1 Construction of the Irrigation Canal Water Balance Algorithm. The irrigation canal draws water from the river, passing through n stages of canals before reaching the farmland. The algorithm for drawing water from the river to the farmland is as follows:

[0129] WF = WDI-EC n -WU=C n -WU

[0130] Wherein, WF is the amount of water delivered to the fields; WDI is the amount of water diverted from the river; EC is the evaporation from the irrigation canal; n represents different levels of irrigation canals, 1, 2, 3, ..., n; WU is the amount of unused water that has not been used for farmland; and C is the amount of water retained in different levels of irrigation canals.

[0131] 3.2 Water Evaporation Algorithm Construction. Water evaporation is calculated using Dalton's theorem, modified for suitability of the study area:

[0132]

[0133] Where E is the saturated vapor pressure at the water surface temperature (3170 Pa = 31.7 hPa at 25℃); e150 is the actual vapor pressure at a height of 150 cm above the water surface; u 150 The sum of wind speed (u1) and current velocity (u2) at a depth of 150 cm above the water surface is expressed in m / s.

[0134] 3.3 Construction of water vapor pressure algorithm.

[0135] 1) Calculation of saturated water vapor pressure:

[0136]

[0137] Where t represents degrees Celsius.

[0138] 2) Calculation of actual water vapor pressure:

[0139] e = Ef

[0140] Where f represents relative humidity. Relative humidity directly reflects the degree to which the air is not saturated. When f = 100%, the air is saturated; when unsaturated, f < 100%; and when supersaturated, f > 100%. The magnitude of relative humidity is not only related to the water vapor content in the atmosphere, but also decreases as the temperature rises. When the water vapor pressure remains constant, as the temperature rises, the saturated water vapor pressure increases, and the relative humidity decreases.

[0141] 3.4 Construction of the 40-minute scale algorithm. Due to the influence of Earth's rotation, the evaporation trend, primarily affected by temperature, exhibits a periodic fluctuation following a cosine function. Steps 3.1 to 3.3 describe the diurnal scale algorithm. Building upon this, to more accurately calculate water evaporation, a cosine function is introduced to calculate water evaporation on a 40-minute scale. The simplified formula is as follows:

[0142]

[0143] Where EC is the instantaneous evaporation rate; c0 is the average evaporation rate, which is controlled by the average temperature; A is the water evaporation amplitude, which is controlled by the minimum and maximum temperatures; c is the radial frequency of water evaporation; and t is the unit time on a 40-minute scale. This represents the lag time of water evaporation in response to temperature. The simulation period is from 10:00 AM to 10:00 AM the following day, with 40 minutes as the basic unit of calculation.

[0144] Step 4: Construct an algorithm for farmland surface water transport.

[0145] 4.1 Construction of the water balance algorithm for the irrigation canal. Water first enters the surface layer (T) of the farmland. The dynamic balance formula for the farmland surface layer is:

[0146] PSA = P + WF - EF + RSA + W sa -W sb

[0147] 4.2 Surface Water Infiltration into Groundwater (PSA) Algorithm Construction. When the water content of a layer exceeds its field capacity and the underlying layer is unsaturated, water will infiltrate. When the soil layer is frozen, no water flows out of the soil layer. The permeable water volume in the soil layer can be calculated using the following formula:

[0148] SW ly,ex =SW ly -FC ly

[0149] Among them, SW ly,ex SW represents the permeable water volume of a soil layer on a certain day, in mm. ly This indicates the soil moisture content on a given day, expressed in mm; FC lyThis represents the field water holding capacity of the soil layer, in mm. The amount of water that infiltrates from the upper layer to the lower layer is calculated using the storage calculus method.

[0150] The calculation equation is as follows:

[0151]

[0152] Among them, w pere,ly Δt represents the amount of water that seeps into the lower soil layer on a certain day, in mm; Δt represents the time step, in h; TT pere This represents the infiltration time, expressed in hours (h). The infiltration time varies for each layer, and the formula is as follows:

[0153]

[0154] Among them, SAT ly FC represents the saturated water content of the soil layer, in mm. ly Indicates the field water holding capacity of the soil layer, mm; K sat This represents the saturated permeability coefficient of the layer, in mm / h.

[0155] 4.3 Construction of Farmland Evapotranspiration (EF) Algorithm.

[0156] Total farmland inflow - seepage = evaporation = water surface evaporation + soil evaporation (40 min):

[0157] When the total water diversion volume exceeds 100% soil moisture content, the water surface evaporation procedure shall be executed;

[0158] When the total water diversion is less than or equal to 100% soil moisture content, or when the total water diversion minus evaporation minus infiltration is less than or equal to 100% soil moisture content, the soil evaporation procedure shall be executed.

[0159] When the total water intake or water content is greater than or equal to the maximum field capacity, the evaporation rate is equal to Esoil,ly.

[0160] When the total water intake or water content is less than the field capacity, the evaporation rate is calculated as: Esoil,ly * exp[2.5(water content - field capacity) / (field capacity - wilting water content)]. The wilting water content is 0 during winter irrigation. The specific calculation method is as follows:

[0161] 1) Potential evapotranspiration calculation:

[0162]

[0163] Where λ represents latent heat of vaporization, MJ / kg; E0 represents potential evapotranspiration, mm / d; H0 represents extraterrestrial radiation (mean radiation converted to a wave-like pattern over a 40-minute timescale), MJ / (m²). 2 d). Tmx represents the highest temperature of a day, in °C; Tmn represents the lowest temperature of a day, in °C; This indicates the average temperature on a given day, expressed in °C.

[0164] 2) Calculation of water surface evaporation:

[0165] In the initial stage of irrigation, water enters the farmland and forms a surface, where evaporation occurs. Currently, surface evaporation is calculated using daily and 40-minute timescales. The evaporation rate is calculated using the irrigation canal evaporation formula, where the flow velocity v2 is set to 0, representing the evaporation rate from a stationary water surface in the field, and the area is set to the irrigated farmland area. The formula is shown in step 3.2.

[0166] 3) Soil evaporation calculation:

[0167] When soil evaporation occurs, the evaporation rate is divided into different soil layers. The depth distribution used to determine the maximum evaporable water volume is as follows:

[0168]

[0169] Where Esoil,z represents the evaporation at depth z, in mm; represents the potential evapotranspiration of the soil on a certain day, in mm; and z represents the burial depth, in mm.

[0170] 4.4 Construction of the algorithm for water recharge of farmland surface from groundwater layer (RSA).

[0171] RSA (revap) only occurs when the water storage in the shallow aquifer exceeds a user-defined threshold. The maximum amount of water that can migrate from the aquifer via RSA on a given day is:

[0172] w revap,mx =β rev ×E0

[0173] Among them, w revap,mx βrev represents the maximum amount of water entering the soil zone due to insufficient soil moisture, in mm; E0 represents the potential evapotranspiration on a given day, in mm. The actual revap amount on a given day is:

[0174]

[0175] w revap =w revap,mx -aq shthr,rvp aq shthr,rvp <aq sh <(aq) shthr,rvp +w revap m,x )

[0176] w revap =w revap,mx q sh ≥(aq shthr,rvp +w revap,mx )

[0177] where, w revap represents the actual water volume entering the soil zone due to insufficient soil moisture, in mm; w revap,mx represents the maximum water volume entering the soil zone due to insufficient soil moisture, in mm; aq sh represents the initial water storage in the shallow aquifer on the i-th day, in mm; aq shthr,rvp represents the water level threshold in the shallow aquifer when revap occurs, in mm.

[0178] Step 5: Construct the algorithm for groundwater migration in farmland.

[0179] Establish the dynamic balance formula for the underground layer in farmland as:

[0180] RFD i = PSA - RSA - PI + IS i - W ua + W ub

[0181] The calculation method for groundwater recharge to rivers and drainage ditches takes the hydraulic gradient as the core, uses Darcy's law to describe the seepage relationship between river water and groundwater, and calculates the total recharge along the river course through an integral formula.

[0182] 5.1 Construction of the hydraulic gradient algorithm for rivers, drainage ditches and groundwater.

[0183] The main driving force for groundwater recharge to rivers and drainage ditches is the hydraulic gradient between river water and groundwater, which is defined as:

[0184] ΔH = hr - hg

[0185] where, ΔH is the hydraulic gradient; hr is the river water level height; hg is the groundwater level height. When hr > hg, river water recharges groundwater; when hr < hg, groundwater recharges the river course.

[0186] 5.2 Construction of the seepage relationship algorithm between river water and groundwater. The seepage between river water and groundwater is described by Darcy's law:

[0187] Q = KsA × ΔH / d

[0188] where, Q is the seepage flow rate (the water volume passing through a unit area per unit time, m 3 / s); Ks is the permeability coefficient of the riverbed sediment (m / s); A is the seepage area (m 2 ); ΔH is the hydraulic gradient; d is the thickness of the riverbed sediment (m).

[0189] 5.3 Construction of the algorithm for rivers and drainage ditches to recharge groundwater. In large-scale studies, the total amount of groundwater recharge by rivers and drainage ditches is calculated using the following formula:

[0190]

[0191] Where G is the total supply (m³) 3 / s); L is the river channel length (m); B(x) is a function of the riverbed width, which varies with x; hr(x) and hg(x) are the distributions of river water level and groundwater level with the river channel length, respectively.

[0192] 5.4 Algorithm Construction Based on the Influence of River Evapotranspiration. When calculating groundwater recharge channels, the influence of river evapotranspiration must be considered. Evapotranspiration can be calculated using empirical formulas:

[0193] E = α × P × exp(-β × d)

[0194] Where E is the evapotranspiration rate (m³) 3 / s); β is the empirical coefficient; P is the potential evapotranspiration.

[0195] 5.5 Construction of the algorithm for dynamic changes in groundwater recharge. Under unsteady conditions, the dynamic changes in the groundwater recharge channel can be described by the following continuity equation:

[0196]

[0197] Where S represents the storage capacity of the river channel and groundwater system; Qin represents the inflow into the river channel; and Qout represents the outflow from the river channel. Calculations of groundwater recharge into rivers typically involve numerical simulation, using the finite element method to solve the governing equations.

[0198]

[0199] Where h is the head (m); K is the permeability tensor; and R is the source and sink term (such as river replenishment or pumping).

[0200] 5.6 Water infiltrates into groundwater from drainage ditches (ISi). The value of i is generally 1. From farm canals to drainage ditches, water infiltrates into groundwater from the farm canals. The PSA algorithm is adopted, see step 4.2.

[0201] 5.7 Water infiltration from drainage ditches into groundwater (RFDi). A value of i = 0 indicates that groundwater directly enters the Yellow River; values ​​of i = 1, 2, 3… indicate that groundwater enters the drainage ditch primarily due to water potential difference. The formula for calculating RFDi is:

[0202] RFD i =S×(d1+d2)×h / 2

[0203] Where S is the length of the ditch (m); d1 and d2 are the upper and lower bottoms of the drainage ditch (m); and h is the height (m). The inner slope ratio is 1:2, and the groundwater volume conversion formula is as follows:

[0204] RFD i =S×(d2+Wub-hi)×(Wub-hi) / 2

[0205] Where Wub is the groundwater volume (m) after irrigation; hi is the groundwater level difference before and after irrigation.

[0206] Step 6: Construct a drainage ditch water transport algorithm.

[0207] When farmland groundwater recharges into drainage ditches, the dynamic balance formula for the water volume in the drainage ditches is as follows:

[0208] WDR = WU + RFD i -ED i

[0209] Groundwater drainage is represented by RFD0, and dry ditch drainage by RFD4. The evaporation formula is given in step 3.2, and the algorithm for farmland groundwater recharge and drainage ditches is given in step 3.5. In the drainage ditch algorithm, Manning's formula describes the water flow velocity and flow rate within the ditch, Darcy's law characterizes the bottom seepage process, the water balance equation quantifies the dynamic changes in water volume, and Saint-Venant's equation simulates the propagation process of water waves.

[0210] 6.1 Water Conveying Capacity Algorithm Construction. The Manning formula is used to describe the water flow velocity v and flow rate Q within the drainage ditch:

[0211]

[0212] Q = v × A

[0213] Where v is the flow velocity (m / s); n is the Manning roughness coefficient; Rh is the hydraulic radius (m), defined as the wetted cross-sectional area A divided by the wetted perimeter P; S is the ditch slope; A is the wetted cross-sectional area (m²). 2 ).

[0214] 6.2 Leakage Rate Algorithm Construction. Leakage at the bottom of the drainage ditch can be described by Darcy's Law:

[0215]

[0216] Where q is the seepage rate per unit area (m / s); Ks is the soil permeability coefficient at the bottom of the ditch (m / s); H is the hydraulic gradient between the water depth and the groundwater level; and d is the thickness of the soil at the bottom of the ditch.

[0217] 6.3 Construction of Dynamic Water Balance Algorithm for Drainage Ditches. The dynamic changes in water volume within the drainage ditch satisfy the water continuity equation:

[0218]

[0219] Where V is the water volume in the drainage ditch; Qin is the amount of water entering the drainage ditch; Qout is the amount of water flowing out of the drainage ditch; L is the leakage loss; and E is the evaporation loss.

[0220] 6.4 Construction of Water Wave Propagation Algorithm. Under dynamic conditions, water transport within the drainage ditch can be described by the Saint-Venant equation:

[0221]

[0222] Where h is the water depth; Q is the flow rate; A is the wetted cross-sectional area; g is the gravitational acceleration; and n is the Manning roughness coefficient.

[0223] 6.5 Water entering agricultural ditches (WU). Options include whether water enters agricultural ditches and the percentage entering. Calculation formula:

[0224] WF(10 8 m 3 )=C4×i

[0225] This method can be used to assess winter irrigation water use in farmland. After water-saving winter irrigation, the water transport path shifts from being dominated by drainage ditches to primarily involving groundwater discharge into the Yellow River. Existing water transport algorithms cannot accurately describe this change, and reasonable improvements in winter irrigation water use after water saving urgently require scientific methods based on accurate assessment. In the Ningxia section of the Yellow River basin, predictions were made with the overall 34-day winter irrigation period remaining unchanged, but delayed by 1 to 8 days for water savings. The prediction results show that delaying winter irrigation can effectively improve the water transport efficiency in the irrigation canals. Delaying winter irrigation by 1 day resulted in a water saving of 5.32 × 10⁻⁶ cubic meters during the winter irrigation period in the study area. 6 m 3 The water allocation per hectare of farmland increased by 18m. 3 The water diversion efficiency increased by 1.6%; the water saving during the winter irrigation period in the study area was 42.47 cubic meters per second due to the 8-day extension of irrigation. 6 m 3 The water allocation per hectare of farmland increased by 143m³ 3 The water diversion efficiency increased by 12.8%. At the same time, the soil freezing rate increased due to the decrease in temperature, which can improve soil moisture in the second year.

[0226] It should be understood that those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A method for assessing the migration process of winter irrigation water in farmland, characterized in that, Includes the following steps: Step 1: Selection of research area, research time, and validation area; The selection principles for the study area, study period, and validation area include the following: the completeness of the irrigation and drainage system; the representativeness of the study period; the typicality of the validation area; and the feasibility of technical and data support. Step 2: Analyze the winter irrigation water transport path in the study area, dividing it into four levels: "irrigation canal - farmland surface water - farmland groundwater - drainage ditch," and construct a water transport system; analyze the water transport path of the irrigation canal; analyze the water transport path of the farmland surface water; analyze the water transport path of the farmland groundwater; analyze the water transport path of the drainage ditch; construct the water transport system; based on the analyzed structure, construct a complete winter irrigation water transport system; the analysis of the winter irrigation water transport path in the study area includes the following steps: Analysis of the water transport path of the diversion canal: Yellow River water (WDI) is diverted to the diversion canal (Cn), and after evaporation loss (ECn) and human loss (WU), it is diverted to farmland for irrigation (WF). Analysis of the surface water transport path in farmland: irrigation water (WF) and rainfall water (P) reach the farmland, and after evaporation (EF) and pumped irrigation (PI), the water infiltrates into groundwater (PSA), with some water replenishing the surface water (RSA); the farmland water content before irrigation is Wsa, and the farmland water content after irrigation is Wsb. Analysis of the groundwater migration path in farmland: Surface water infiltrates into the farmland groundwater PSA, then flows through the irrigation ditch IS1, the surface water replenishment RSA, and the pumped irrigation PI before flowing into the drainage ditch RFDi and the Yellow River RFD0; the groundwater level before irrigation is Wua, and the groundwater level after irrigation is Wub; Analysis of the water transport path in the drainage ditch: After the groundwater flows to the drainage ditch RFD1Dn, it undergoes evaporation loss EDn and then flows into the Yellow River WDR; Step 3: Construct water transport algorithms for the irrigation canal; the construction of water transport algorithms for the irrigation canal includes: water balance algorithm, water evaporation algorithm, water vapor pressure algorithm, and 40-minute scale algorithm; The specific steps involved in constructing the water transport algorithm for the irrigation canal include: The water balance algorithm for the irrigation canal is constructed as follows: the irrigation canal draws water from the river, and after passing through n stages of irrigation canals, it reaches the farmland; the algorithm for drawing water from the river to the farmland is as follows: WF=WDI-EC n -WU=C n -WU Where WF is the water volume delivered to the fields; WDI is the water volume diverted from the river; EC is the evaporation from the irrigation canal; n represents different levels of irrigation canals, 1, 2, 3, ..., n; WU is the unused water volume that has not reached farmland; and C is the water retention volume of different levels of irrigation canals. The water evaporation algorithm is constructed as described above; water evaporation is calculated using Dalton's theorem, modified for suitability of the study area. Where E is the saturated vapor pressure at the water surface temperature, which is 3170 Pa at 25℃; e150 is the actual vapor pressure at a height of 150 cm above the water surface; u 150 The sum of wind speed u1 and current velocity u2 at a point 150cm above the water surface is expressed in m / s. The water vapor pressure algorithm described above is constructed as follows: 1) Calculation of saturated water vapor pressure: Where t is in degrees Celsius; 2) Calculation of actual water vapor pressure: e = Ef Where f is the relative humidity; relative humidity directly reflects the degree to which the air is not saturated; when f = 100%, the air is saturated; when it is unsaturated, f < 100%; when it is supersaturated, f > 100%; the magnitude of relative humidity is not only related to the water vapor content in the atmosphere, but also decreases as the temperature rises; when the water vapor pressure remains constant, as the temperature rises, the saturated water vapor pressure increases, and the relative humidity decreases. Construction of the 40 - minute scale algorithm; affected by the earth's rotation, the evaporation trend under the main influence of temperature fluctuates periodically in a cosine function; the cosine function is introduced to calculate the water evaporation on a 40 - minute scale; the simplified formula is as follows: Where EC is the instantaneous evaporation rate; c0 is the average evaporation rate, which is controlled by the average temperature; A is the water evaporation amplitude, which is controlled by the minimum and maximum temperatures; c is the radial frequency of water evaporation; and t is the unit time on a 40-minute scale. The lag time for water evaporation in response to temperature; the simulation time is from 10:00 AM to 10:00 AM the next day, with 40 minutes as the basic calculation unit; Step 4: Construction of the farmland surface water migration algorithm; the construction of the farmland surface water migration algorithm includes: construction of the water balance algorithm for the diversion canal; construction of the PSA algorithm for surface water infiltration into groundwater; construction of the EF algorithm for farmland evapotranspiration; construction of the RSA algorithm for the water supply from the groundwater layer to the farmland surface; Construction of the water balance algorithm for the diversion canal; construction of the PSA algorithm for surface water infiltration into groundwater; construction of the EF algorithm for farmland evapotranspiration; construction of the RSA algorithm for the water supply from the groundwater layer to the farmland surface; For the method described above, in step 4, the construction of the farmland surface water migration algorithm is specifically as follows: Construction of the water balance algorithm for the diversion canal; the diverted water first enters the farmland surface layer T; the dynamic balance formula for the farmland surface layer is: PSA=P+WF-EF+RSA+W sa -W sb Construction of the PSA algorithm for surface water infiltration into groundwater; when the water content of a certain layer exceeds its field capacity and the lower layer is unsaturated, water will infiltrate; when the soil layer is frozen, no water flows out of the soil layer; the permeable water volume in the soil layer can be calculated by the following formula: SW ly,ex =SW ly -FC ly Among them, SW ly,ex SW represents the permeable water volume of a soil layer on a certain day, in mm. ly This indicates the soil moisture content on a given day, expressed in mm; FC ly The field water holding capacity of the soil layer is expressed in mm; the amount of water infiltrating from the upper layer to the lower layer is calculated using the storage calculus method; the calculation equation is: Among them, w pere,ly Δt represents the amount of water that seeps into the lower soil layer on a certain day, in mm; Δt represents the time step, in h; TT pere The infiltration time is expressed in hours (h). The infiltration time varies for each layer and is calculated using the following formula: Among them, SAT ly FC represents the saturated water content of the soil layer, in mm. ly Indicates the field water holding capacity of the soil layer, mm; K sat This represents the saturated permeability coefficient of the layer, in mm / h; Construction of the EF algorithm for farmland evapotranspiration; Total water inflow into the farmland - leakage = evaporation amount = water surface evaporation + 40 - minute soil evaporation: When the total diverted water volume > 100% water content of the soil, execute the water surface evaporation program; When the total diverted water volume ≤ 100% water content of the soil or the total diverted water volume - evaporation amount - infiltration amount ≤ 100% water content of the soil, execute the soil evaporation program; When the total diverted water volume or water content ≥ the maximum field capacity, the evaporation amount = Esoil,ly; When the total diverted water volume or water content < the maximum field capacity, the evaporation amount = Esoil,ly * exp[2.5 (water content - field capacity) / (field capacity - wilting coefficient)]; the wilting coefficient is 0 during winter irrigation; Construction of the RSA algorithm for the water supply from the groundwater layer to the farmland surface; RSA occurs only when the water storage in the shallow aquifer exceeds the user - defined threshold; the maximum amount of water migrating from the aquifer through RSA (revap) on a certain day is: w revap,mx =b rev ×E0 Among them, w revap,mx The maximum amount of water entering the soil zone due to insufficient soil moisture is represented in mm; βrev represents the revap system; E0 represents the potential evapotranspiration on a certain day in mm; the actual revap amount on a certain day is: In revap =0aq sh ≤aq shthr,rvp w revap =w revap,mx -pork shthr,rvp pork shthr,rvp <aq sh <(aq shthr,rvp +w revap,mx ) w revap =w revap,mx q s h≥(aq shthr,rvp +w revap,mx ) Among them, w revap This indicates the actual amount of water entering the soil zone due to insufficient soil moisture, expressed in mm; w revap,mx This indicates the maximum amount of water entering the soil zone due to insufficient soil moisture, expressed in mm; aq sh aq represents the initial water storage of the shallow aquifer on day i, in mm; shthr,rvp This represents the water level threshold of the shallow aquifer when a revap occurs, in mm; Step 5: Construction of the farmland groundwater migration algorithm; the construction of the farmland groundwater migration algorithm includes: Establish the dynamic balance formula for the farmland underground layer as: RFD i =PSA-RSA-PI+IS i -W ua +W ub The calculation method for groundwater recharge to the river channel and drainage ditch takes the hydraulic gradient as the core, uses Darcy's law to describe the seepage relationship between river water and groundwater, and calculates the total recharge amount along the river channel through an integral formula; Construction of the hydraulic gradient algorithm for the river channel, drainage ditch and groundwater; The main driving force for groundwater to recharge the river channel and drainage ditch is the hydraulic gradient between river water and groundwater, which is defined as: ΔH = hr - hg Where, ΔH is the hydraulic gradient; hr is the river water level height; hg is the groundwater level height; when hr > hg, river water recharges groundwater; when hr < hg, groundwater recharges the river channel; Construction of the seepage relationship algorithm between river water and groundwater; the seepage between river water and groundwater is described by Darcy's law: Q = KsA × ΔH / d Where Q is the seepage flow rate, the amount of water passing through a unit area per unit time, in meters (m). 3 / s; Ks is the permeability coefficient of the riverbed sediment, m / s; A is the seepage area, m². 2 ΔH is the hydraulic gradient; d is the thickness of the riverbed sediments, in meters. Algorithm for groundwater recharge from rivers and drainage ditches: In large-scale studies, the total amount of groundwater recharged by rivers and drainage ditches is calculated using the following formula: Where G is the total supply (m³) 3 / s); L is the river channel length (m); B(x) is a function of the riverbed width, which varies with x; hr(x) and hg(x) are the distributions of river water level and groundwater level with river channel length, respectively; River evapotranspiration affects algorithm construction; when calculating groundwater recharge channels, the impact of river evapotranspiration must be considered; evapotranspiration can be calculated using empirical formulas. E = α × P × exp(-β × d) Where E is the evaporation rate m 3 / s; β is an empirical coefficient; P is the potential evapotranspiration; A dynamic change algorithm for groundwater recharge is constructed. Under unsteady conditions, the dynamic changes of the groundwater recharge channel can be described by the following continuity equation: Where S is the storage capacity of the river channel and groundwater system; Qin is the inflow into the river channel; and Qout is the outflow from the river channel. The calculation of groundwater recharge into the river channel typically involves numerical simulation, using the finite element method to solve the governing equations. Where h is the head (m); K is the permeability tensor; and R is the source / sink term. Water infiltrates into groundwater ISi from drainage ditches; the value of i is generally 1. From farm canals to farm ditches, water infiltrates into groundwater from farm ditches; the PSA algorithm is used. Water infiltrates into the groundwater RFDi from the drainage ditch; a value of i of 0 indicates that the groundwater directly enters the Yellow River; a value of i of 1, 2, 3… indicates that the groundwater enters the drainage ditch due to the water potential difference; the formula for calculating RFDi is: RFD i =S×(d1+d2)×h / 2 Where S is the length of the ditch (m); d1 and d2 are the upper and lower bottoms of the drainage ditch (m); h is the height (m); the inner slope ratio is 1:2, and the groundwater volume conversion formula is as follows: RFD i =S×(d2+Wub-hi)×(Wub-hi) / 2 Where Wub is the groundwater volume (m) after irrigation; hi is the groundwater level difference before and after irrigation. Step 6: Construct the drainage ditch water transport algorithm; Constructing the drainage ditch water transport algorithm includes: Water conveyance capacity algorithm construction; Manning's formula is used to describe the water flow velocity v and flow rate Q in the drainage ditch: Q = v × A Where v is the flow velocity (m / s); n is the Manning roughness coefficient; Rh is the hydraulic radius (m), defined as the wetted cross-sectional area A divided by the wetted perimeter P; S is the ditch slope; A is the wetted cross-sectional area (m²). 2 ); Leakage rate algorithm construction; leakage at the bottom of the drainage ditch can be described by Darcy's law: Where q is the seepage rate per unit area (m / s); Ks is the soil permeability coefficient at the bottom of the ditch (m / s); H is the hydraulic gradient between the water depth and the groundwater level; and d is the thickness of the soil at the bottom of the ditch. A dynamic water balance algorithm for drainage ditches is constructed; the dynamic changes in water volume within the drainage ditches satisfy the water continuity equation. Where V is the water volume in the drainage ditch; Qin is the amount of water entering the drainage ditch; Qout is the amount of water flowing out of the drainage ditch; L is the leakage loss; and E is the evaporation loss. Water wave propagation algorithm construction; under dynamic conditions, water transport within the drainage ditch can be described by the Saint-Venant equation: Where h is the water depth; Q is the flow rate; A is the wetted cross-sectional area; g is the gravitational acceleration; and n is the Manning roughness coefficient. Canal water enters agricultural ditch (WU); options include whether to allow water to enter the agricultural ditch and the percentage of water entering the agricultural ditch; calculation formula: WF(10 8 m 3 )=C4×i。 2. An evaluation system for the migration process of winter irrigation water in farmland, characterized in that... It includes: a processor and a memory for storing a computer program capable of running on the processor; wherein, when the processor runs the computer program, it performs the steps of the method of claim 1.

3. A storage medium having a computer program stored thereon, characterized in that... When the computer program is executed by the processor, it implements the steps of the method of claim 1.

4. A computer program product, comprising a computer program, characterized in that... When the computer program is executed by the processor, it implements the steps of the method of claim 1.

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