Evaluation system and method for farmland winter irrigation water transportation process, and storage medium

Abstract

The invention discloses an evaluation system and method for a farmland winter irrigation water transportation process and a storage medium. The evaluation method comprises the following steps: step 1, selecting a research area, research time and a verification area; 2, analyzing a winter irrigation water transportation path of the research area, dividing the winter irrigation water transportation path into four levels of diversion canal-farmland surface layer-farmland underground-drainage ditch, and constructing a water transportation system; 3, constructing a diversion canal water transfer algorithm; 4, constructing a farmland surface water migration algorithm; 5, constructing a farmland groundwater migration algorithm; and step 6, constructing a drainage ditch water transport algorithm. According to the method and the system, the reasonable irrigation and drainage improvement method can be provided by simulating and predicting the irrigation and drainage amount and time. Prediction is carried out in the Ningxia section of the Yellow River basin, the total time of 34 days of the winter irrigation period is kept unchanged, and water saving prediction is carried out by integrally delaying 1-8 days backwards. A prediction result shows that the delayed winter irrigation can effectively improve the transmission efficiency of water in the diversion canal.

Description

Technical Field

[0001] The present invention belongs to the technical field of agricultural water conservation, and specifically relates to an evaluation system, method and storage medium for the water migration process of winter irrigation in farmland. By simulating and predicting the irrigation and drainage volume and time, a reasonable improvement method for irrigation and drainage is proposed. Background Art

[0002] In the context of the global water shortage, agricultural water conservation is used to address this challenge. It is generally believed that the utilization efficiency of water resources can be improved by strictly controlling agricultural water consumption. However, this simple way of relying solely on reducing water consumption not only changes the water migration process but also leads to the waste of ditch resources, ignoring the necessity of adjusting management strategies after the change of the water migration path. Winter irrigation is an important agricultural measure to maintain the soil moisture of farmland, and the irrigation volume is determined by relying on the water migration process evaluation method. Under the dual influence of water conservation measures and global warming, the soil freezing rate of winter irrigation in farmland decreases, making it difficult to achieve the ideal goal of salt drainage and soil moisture conservation. In the evaluation method of the water migration process of winter irrigation before water conservation, the water migration in the ditch system is emphasized, and it is easy to meet the threshold of underground water content. However, after water conservation, the winter irrigation water first meets the threshold of underground water content and then uses the ditch system for water migration. Generally speaking, when the evaluation method of the water migration process of winter irrigation before water conservation is applied after water conservation, there are two problems: 1) The evaluation result is inaccurate, resulting in a serious reduction in the winter irrigation water quota; 2) It is difficult to achieve a reasonable evaluation 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 water migration process of winter irrigation in farmland in view of the deficiencies of the prior art.

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

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

[0006] Step 1: Selection of the study area, study time and verification area;

[0007] Step 2: Analyze the water migration path of winter irrigation in the study area, which is divided into 4 levels of "diversion canal - farmland surface - farmland underground - drainage ditch", and construct a water migration system;

[0008] Step 3: Construct a water migration algorithm for the diversion canal;

[0009] Step 4: Construct a water migration algorithm for the farmland surface;

[0010] Step 5: Construct a water migration algorithm for the farmland underground water;

[0011] Step 6: Construct a water migration algorithm for the drainage ditch.

[0012] For the method described above, in step 2, parsing the winter irrigation water migration path in the study area includes the following steps: parsing the water migration path of the water diversion canal; parsing the water migration path of the farmland surface layer; parsing the water migration path of the farmland groundwater; parsing the water migration path of the drainage ditch; constructing a water migration system; and constructing a complete winter irrigation water migration system according to the parsed structure.

[0013] For the method described above, in step 2, parsing the winter irrigation water migration path in the study area includes the following steps:

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

[0015] Parsing the water migration path of the farmland surface layer: Farmland irrigation (WF) and rainfall (P) water reach the farmland. After farmland water evaporation (EF) and pumping irrigation (PI), it infiltrates into the groundwater (PSA), and part of the water recharges the surface (RSA). The water content of the farmland before irrigation is Wsa, and the water content of the farmland after irrigation is Wsb;

[0016] Parsing the water migration path of the farmland groundwater: The farmland surface water infiltrates into the farmland underground (PSA). After infiltration through the farm ditch (IS1), surface recharge (RSA), and pumping irrigation (PI), it flows to the drainage ditch (RFDi) and the Yellow River (RFD0). The groundwater level before irrigation is Wua, and the groundwater level after irrigation is Wub;

[0017] Parsing the water migration path of the drainage ditch: After the groundwater flows into the drainage ditch (RFDi) and then (Dn), after evaporation loss (EDn), it flows into the Yellow River (WDR).

[0018] For the method described above, in step 3, constructing the water migration algorithm for the water diversion canal includes: constructing the water balance algorithm for the water diversion canal; constructing the water evaporation algorithm; constructing the water vapor pressure algorithm; and constructing the 40-minute scale algorithm.

[0019] For the method described above, in step 3, constructing the water migration algorithm for the water diversion canal specifically includes:

[0020] Constructing the water balance algorithm for the water diversion canal; The water diversion canal diverts water from the river and reaches the farmland after passing through n-level water diversion canals. The algorithm for the water diversion canal diverting water from the river to the farmland is as follows:

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

[0022] Among them, WF is the water volume reaching the farmland; WDI is the water volume diverted from the river; EC is the evaporation volume of the water diversion canal; n is the water diversion canals at different levels, 1, 2, 3, …, n; WU is the unused water volume that has not passed through the farmland; C is the retention volume of the water in the water diversion canals at different levels.

[0023] Construction of the water evaporation algorithm; water evaporation is calculated using Dalton's theorem modified according to the suitability of the study area:

[0024]

[0025] Among them, E is the saturated water vapor pressure at the water surface temperature, which is 3170 Pa at 25 °C; e150 is the actual water vapor pressure at 150 cm above the water surface; u 150 is the wind speed (u1) + flow velocity (u2) at 150 cm above the water surface, with the unit of m / s;

[0026] Construction of the water vapor pressure algorithm:

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

[0028]

[0029] Among them, t is in degrees Celsius;

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

[0031] e = Ef

[0032] Among them, f is the relative humidity; the relative humidity directly reflects the degree of saturation of the air; when f = 100%, the air has reached saturation, when it is unsaturated, f < 100%, and when it is supersaturated, f > 100%; the magnitude of the relative humidity is not only related to the water vapor content in the atmosphere, but also decreases with the increase of temperature; when the water vapor pressure remains unchanged, as the temperature rises, the saturated water vapor pressure increases and the relative humidity will decrease;

[0033] Construction of the 40 - minute scale algorithm; affected by the rotation of the earth, the evaporation trend under the main influence of temperature shows a periodic fluctuation in a cosine function; the cosine function is introduced to calculate the water evaporation at the 40 - minute scale; the simplified formula is as follows:

[0034]

[0035] Among them, EC is the instantaneous evaporation volume; c0 is the average evaporation volume, controlled by the average temperature; A is the amplitude of water evaporation, controlled by the minimum temperature and the maximum temperature; c is the radial frequency of water evaporation; t is the unit time at the 40 - minute scale; is the lag time of water evaporation's response to temperature; the simulation time is from 10:00 to 10:00 the next day, and 40 minutes is the basic calculation unit.

[0036] In the method described above, in step 4, constructing the surface water migration algorithm for farmland includes: constructing the water balance algorithm for the diversion canal; constructing the PSA algorithm for surface water infiltration into groundwater; constructing the evapotranspiration (EF) algorithm for farmland; constructing the RSA algorithm for water recharge from the groundwater layer to the farmland surface.

[0037] In the method described above, in step 4, constructing the surface water migration algorithm for farmland specifically is:

[0038] Constructing 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:

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

[0040] Constructing 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:

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

[0042] Among them, SW ly,ex represents the permeable water volume of the soil layer on a certain day, mm; SW ly represents the water content of the soil layer on a certain day, mm; FC ly represents the field capacity of the soil layer, mm; the water volume infiltrating from the upper layer to the lower layer is calculated by the storage calculus method.

[0043] The calculation equation is:

[0044]

[0045] Among them, w pere,ly represents the water volume infiltrating into the lower soil layer on a certain day, mm; Δt represents the time step, h; TT pere represents the infiltration time, h; the infiltration time of each layer is different, and the calculation formula is:

[0046]

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

[0048] Constructing the evapotranspiration (EF) algorithm for farmland;

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

[0050] When the total water diversion volume > 100% soil water content, execute the water surface evaporation program;

[0051] When the total water diversion volume ≤ 100% soil water content or total water diversion volume - evaporation - infiltration ≤ 100% soil water content, execute the soil evaporation program;

[0052] When the total water diversion volume or water content ≥ field maximum water holding capacity, evaporation = Esoil,ly;

[0053] When the total water diversion volume or water content < field maximum water holding capacity, evaporation = Esoil,ly * exp[2.5 (water content - field water holding capacity) / (field water holding capacity - wilting water content)]; The wilting water content is 0 during winter irrigation;

[0054] Construction of the algorithm for the water recharge (RSA) from the groundwater layer to the farmland surface;

[0055] 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) in a day is:

[0056] w revap,mx = β rev × E 0

[0057] where, w revap,mx represents the maximum amount of water entering the soil zone due to insufficient soil moisture, mm; βrev represents the revap coefficient; E0 represents the potential evapotranspiration in a day, mm; The actual revap amount in a 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] where, w revapRepresents the actual amount of water entering the soil zone due to insufficient soil moisture, in mm; w revap,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] In 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 the 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 channels and drainage ditches to recharge groundwater; In large-scale studies, the total amount of groundwater recharge by river channels and drainage ditches is calculated using the following formula:

[0074]

[0075] where G is the total recharge amount (m 3 / s); L is the river channel length (m); B(x) is a function of the riverbed width, varying with x; hr(x) and hg(x) are the distributions of the river water level and the groundwater level along the river channel length, respectively;

[0076] Construction of the algorithm for the influence of river channel evapotranspiration; When calculating the groundwater recharge to the river channel, the influence of river channel evapotranspiration needs to be considered; The evapotranspiration amount can be calculated by an empirical formula:

[0077] E = α × P × exp(-β × d)

[0078] where E is the evapotranspiration amount (m 3 / s); β is the empirical coefficient; P is the potential evapotranspiration amount;

[0079] Construction of the algorithm for the dynamic change of groundwater recharge; Under unsteady conditions, the dynamic change of groundwater recharge to the river channel can be described by the following continuity equation:

[0080]

[0081] where S is the storage volume of the river channel and groundwater system; Qin is the recharge amount entering the river channel; Qout is the outflow amount leaving the river channel; The calculation of groundwater recharge to the river channel usually combines numerical simulation and solves the governing equation by the finite element method:

[0082]

[0083] where h is the hydraulic head, m; K is the permeability coefficient tensor; R is the source-sink term;

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

[0085] Water infiltrates from the drainage ditch into the groundwater (RFDi); The value of i is 0, indicating that the groundwater directly enters the Yellow River; The value of i is 1, 2, 3..., indicating that the groundwater enters the drainage ditch, relying on the water potential difference; The calculation formula for 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 according to the groundwater volume conversion formula:

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

[0089] Among them, Wub is the underground water volume after irrigation (m); hi is the difference in the underground water level before and after irrigation.

[0090] In the method described above, in step 6, constructing the drainage ditch water migration algorithm includes:

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

[0092]

[0093] Q = v × A

[0094] Among them, 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 channel slope; A is the wetted cross-sectional area (m 2 );

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

[0096]

[0097] Among them, q is the leakage 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 underground water level; d is the thickness of the soil at the bottom of the ditch;

[0098] Constructing the drainage ditch water dynamic balance algorithm; the dynamic change of the water volume in the drainage ditch satisfies the water continuity equation:

[0099]

[0100] Among them, V is the water volume in the drainage ditch; Qin is the water volume entering the drainage ditch; Qout is the water volume flowing out of the drainage ditch; L is the leakage loss; E is the evaporation loss;

[0101] Constructing the water wave propagation algorithm; under dynamic conditions, the water migration in the drainage ditch can be described by the Saint-Venant equation:

[0102]

[0103]

[0104] Among them, h is the water depth; Q is the flow rate; A is the wetted cross-sectional area; g is the acceleration due to gravity; n is the Manning roughness coefficient;

[0105] Water from the canal enters the agricultural ditch (WU); it is optional whether to enter the agricultural ditch and what proportion enters the agricultural ditch; the calculation formula:

[0106] WF(10 8 m 3) = C4 × i。

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

[0108] An evaluation system for the winter irrigation water migration process in farmland, comprising: a processor and a memory for storing a computer program capable of running on the processor; wherein, when the processor is used to run the computer program, it executes the steps of any one of the described methods.

[0109] A storage medium, on which a computer program is stored, characterized in that when the computer program is executed by a processor, it implements the steps of any one of the described methods.

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

[0111] Compared with the prior art, the following beneficial effects are achieved:

[0112] The evaluation of the winter irrigation water migration process after water conservation is more accurate. The present invention constructs an algorithm based on the water migration process after winter irrigation water conservation, and constructs a water migration system and algorithm system of "diversion canal - farmland surface - farmland underground - drainage ditch". It is applied in the Ningxia section of the Yellow River Basin. During the winter irrigation period from 2020 to 2023, 3 main canals entering the Yellow River are selected for monitoring, namely the Fifth Drainage Ditch, the Middle Main Ditch, and the Luo River. 411 groups of data are obtained in 4 years for verification. In the verification results, R 2 is 0.72, NSE is 0.67, RMSE is 0.10, and Pbias is 7.04%, and the accuracy is reliable.

[0113] Reasonable prediction of winter irrigation water is realized. Through the simulation and prediction of the irrigation and drainage volume and time, reasonable improvement methods for irrigation and drainage are proposed. As time delays, the evaporation amount significantly decreases. Prediction is carried out in the Ningxia section of the Yellow River Basin. The overall time of 34 days during the winter irrigation period remains unchanged, and the overall prediction of water saving is delayed by 1 to 8 days. The prediction results show that delaying winter irrigation can effectively improve the water transmission efficiency in the diversion canal. Delaying winter irrigation by 1 day, the water saved in the study area during the winter irrigation period is 5.32×10 6 m 3 , the water allocation per hectare of farmland increases by 18 m 3 , and the water diversion efficiency increases by 1.6%; delaying irrigation by 8 days, the water saved in the study area during the winter irrigation period is 42.47×10 6 m 3 , the water allocation per hectare of farmland increases by 143 m 3, the water diversion efficiency is increased by 12.8%. At the same time, affected by the temperature drop, the soil freezing rate increases, which can improve the soil moisture content in the following year. Description of the Drawings

[0114] Figure 1 It is an analysis diagram of the water movement process after winter irrigation water conservation in farmland; Detailed Implementation Modes

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

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

[0117] 1.1 Completeness of the irrigation and drainage system. The study area should be selected in an area with complete irrigation and drainage facilities to ensure that there is sufficient water conservancy infrastructure to support the monitoring of the winter irrigation water movement process;

[0118] 1.2 Representativeness of the study time. The selected study time should be able to cover different climate and hydrological conditions in order to obtain the change data of the water movement process 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 water movement characteristics under different land use types, soil types, and crop planting methods;

[0120] 1.4 Feasibility of technical and data support: When selecting the area, it is necessary to ensure that there is a certain technical support and data basis, such as whether there are relevant hydrological data, meteorological data, and soil characteristic data. At the same time, the study area should have conditions suitable for installing monitoring equipment and long-term tracking and monitoring data, facilitating the implementation of an efficient data acquisition and monitoring system to ensure the reliability and comparability of the data.

[0121] Step 2: Analyze the winter irrigation water movement path in the study area, which is divided into 4 levels of "diversion canal - farmland surface - farmland underground - drainage ditch", and construct a water movement system.

[0122] 2.1 Analysis of the water movement path in the diversion canal. The Yellow River water diversion (WDI) reaches the diversion canal (Cn), and after evaporation loss (ECn) and artificial loss (WU), it is diverted to farmland irrigation (WF);

[0123] 2.2 Analysis of the water movement path on the farmland surface. The farmland irrigation (WF) and rainfall (P) water reach the farmland. After the evaporation of farmland water (EF) and pumping irrigation (PI), it infiltrates into the groundwater (PSA), and part of the water replenishes 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 groundwater migration path in farmland. The surface water in the farmland infiltrates into the farmland groundwater (PSA). After infiltration through the farm ditch (IS1), reverse recharge to the surface (RSA), and pumping irrigation (PI), it flows 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;

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

[0126] 2.5 Construction of the water migration system. The structures analyzed in steps 2.1 to 2.4 are used to construct a complete winter irrigation water migration system (such as Figure 1 ).

[0127] Step 3: Construct the water migration algorithm for the water diversion canal.

[0128] 3.1 Construction of the water balance algorithm for the water diversion canal. The water diversion canal diverts water from the river and reaches the farmland after passing through n levels of water diversion canals. The algorithm for diverting water from the river to the farmland by the water diversion canal is as follows:

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

[0130] Where WF is the water volume reaching the farmland; WDI is the water volume diverted from the river; EC is the evaporation volume of the water diversion canal; n is the water diversion canals at different levels, 1, 2, 3,..., n; WU is the unused water volume that has not passed through the farmland; C is the retention volume of water in the water diversion canals at different levels.

[0131] 3.2 Construction of the water evaporation algorithm. The water evaporation is calculated using Dalton's law modified according to the suitability of the study area:

[0132]

[0133] Where E is the saturated water vapor pressure at the water surface temperature (3170 pa = 31.7 hpa at 25°C); e150 is the actual water vapor pressure at 150 cm above the water surface; u 150 is the wind speed (u1) + flow velocity (u2) at 150 cm above the water surface, with the unit of m / s.

[0134] 3.3 Construction of the water vapor pressure algorithm.

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

[0136]

[0137] Where t is in degrees Celsius.

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

[0139] e = Ef

[0140] Among them, f is the relative humidity. The relative humidity directly reflects the degree to which the air is close to saturation. When f = 100%, the air has reached saturation. When it is unsaturated, f < 100%, and when it is supersaturated, f > 100%. The magnitude of the 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 unchanged, as the temperature increases, the saturated water vapor pressure increases and the relative humidity decreases.

[0141] 3.4 Construction of the 40 - minute scale algorithm. Affected by the Earth's rotation, the evaporation trend under the main influence of temperature shows a periodic fluctuation in a cosine function. Steps 3.1 to 3.3 are the daily scale algorithms. On this basis, in order to calculate the evaporation of water more precisely, a cosine function is introduced to calculate the evaporation of water on a 40 - minute scale. The simplified formula is as follows:

[0142]

[0143] Among them, EC is the instantaneous evaporation; c0 is the average evaporation, controlled by the average temperature; A is the amplitude of water evaporation, controlled by the lowest and highest temperatures; c is the radial frequency of water evaporation; t is the unit time on a 40 - minute scale; is the lag time of water evaporation's response to temperature. The simulation time is from 10:00 to 10:00 the next day, and 40 minutes is the basic calculation unit.

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

[0145] 4.1 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:

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

[0147] 4.2 Construction of the algorithm for surface water infiltration into groundwater (PSA). 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:

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

[0149] Among them, SW ly,ex represents the permeable water volume of the soil layer on a certain day, mm; SW ly represents the water content of the soil layer on a certain day, mm; FC lyIndicates the field capacity of the soil layer, in mm. The amount of water infiltrating from the upper layer to the lower layer is calculated using the storage routing method.

[0150] The calculation equation is:

[0151]

[0152] Where, w pere,ly Indicates the amount of water infiltrating into the lower soil layer on a certain day, in mm; Δt represents the time step, in h; TT pere Indicates the infiltration time, in h. The infiltration times of each layer are different, and the calculation formula is:

[0153]

[0154] Where, SAT ly Indicates the saturated water content of the soil layer, in mm; FC ly Indicates the field capacity of the soil layer, in mm; K sat Indicates the saturated hydraulic conductivity of this layer, in mm / h.

[0155] 4.3 Construction of the farmland evapotranspiration (EF) algorithm.

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

[0157] When the total water diversion volume > the water content of the soil at 100%, execute the water surface evaporation program;

[0158] When the total water diversion volume ≤ the water content of the soil at 100% or the total water diversion volume - evaporation amount - infiltration amount ≤ the water content of the soil at 100%, execute the soil evaporation program.

[0159] When the total water diversion volume or water content ≥ the maximum field capacity, the evaporation amount = Esoil,ly;

[0160] When the total water diversion volume or water content < the maximum field capacity, the evaporation amount = Esoil,ly * exp[2.5 (water content - field capacity) / (field capacity - wilting point water content)]. During winter irrigation, the wilting point water content is 0. The specific algorithm is as follows:

[0161] 1) Potential evapotranspiration calculation:

[0162]

[0163] Where, λ represents the latent heat of evaporation, in MJ / kg; E0 represents the potential evapotranspiration amount, in mm / d; H0 represents the extraterrestrial radiation (the average radiation is converted to a fluctuating form on a 40 - min scale), in MJ / (m 2 d). Tmx represents the maximum air temperature on a certain day, in °C; Tmn represents the minimum air temperature on a certain day, in °C; Represents the average temperature of a certain day, in °C.

[0164] 2) Calculation of water surface evaporation:

[0165] In the initial stage of irrigation, water enters the farmland to form a water surface, and water surface evaporation occurs. Currently, water surface evaporation is calculated on a daily scale and a 40-minute scale. The water surface evaporation amount is calculated using the evaporation formula of the diversion canal, where the flow velocity v2 is set to 0, representing the evaporation amount of the static water surface in the field, and the area is set to the area of the farmland in the irrigation area. See Step 3.2 for the formula.

[0166] 3) Calculation of soil evaporation:

[0167] When soil evaporation occurs, the evaporation amounts of different soil layers are divided. The depth distribution used to determine the maximum available evaporation water volume is as follows:

[0168]

[0169] Among them, Esoil,z represents the evaporation amount at depth z, in mm; represents the potential soil evapotranspiration of a certain day, in mm; z represents the burial depth, in mm.

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

[0171] 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) in a certain day is:

[0172] w revap,mx = β rev ×E 0

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

[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 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 the integral formula.

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

[0183] 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:

[0184] ΔH = hr - hg

[0185] Among them, 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.

[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] Among them, 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).

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

[0190]

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

[0192] 5.4 Algorithm construction for the influence of channel evapotranspiration. When calculating the groundwater recharge to the channel, the influence of channel evapotranspiration needs to be considered. The evapotranspiration can be calculated by an empirical formula:

[0193] E = α × P × exp(-β × d)

[0194] where E is the evapotranspiration (m 3 / s); β is the empirical coefficient; P is the potential evapotranspiration.

[0195] 5.5 Algorithm construction for the dynamic change of groundwater recharge. Under unsteady conditions, the dynamic change of groundwater recharge to the channel can be described by the following continuity equation:

[0196]

[0197] where S is the storage in the channel and groundwater system; Qin is the recharge entering the channel; Qout is the outflow leaving the channel. The calculation of groundwater recharge to the channel usually combines numerical simulation and solves the governing equation by the finite element method:

[0198]

[0199] where h is the hydraulic head (m); K is the permeability tensor; R is the source-sink term (such as channel recharge or pumping).

[0200] 5.6 Water infiltration from the drainage ditch into the groundwater (ISi). The value of i is generally 1, from the agricultural canal to the agricultural drainage ditch, and water infiltrates from the agricultural drainage ditch into the groundwater. The PSA algorithm is adopted, as shown in step 4.2.

[0201] 5.7 Water infiltration from the drainage ditch into the groundwater (RFDi). The value of i is 0, indicating that the groundwater directly enters the Yellow River; the values of i are 1, 2, 3..., indicating that the groundwater enters the drainage ditch, mainly relying on the water potential difference. The calculation formula for 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); h is the height (m). The inner slope ratio is 1:2, and according to the groundwater volume conversion formula:

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

[0205] Wherein, Wub is the amount of groundwater after irrigation (m); hi is the difference in groundwater level before and after irrigation.

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

[0207] The farmland groundwater is replenished to the drainage ditch, and the dynamic balance formula of the water volume in the drainage ditch is established as:

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

[0209] The groundwater drainage is RFD0, and the main ditch drainage is RFD4. The evaporation formula is shown in Step 3.2, and the algorithm for the farmland groundwater to replenish the drainage ditch is shown in Step 3.5. For the algorithm in the drainage ditch, the Manning formula is used to describe the water flow velocity and flow rate in the ditch, the Darcy's law depicts the bottom leakage process, the water balance equation quantifies the dynamic change of the water volume, and the Saint-Venant equation simulates the propagation process of the water wave.

[0210] 6.1 Construction of the water conveyance capacity algorithm. The Manning formula is used to describe the water flow velocity v and the flow rate Q in the drainage ditch:

[0211]

[0212] Q = v × A

[0213] Wherein, 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 (m 2 ).

[0214] 6.2 Construction of the leakage rate algorithm. The leakage at the bottom of the drainage ditch can be described by Darcy's law:

[0215]

[0216] Wherein, q is the leakage 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; d is the thickness of the soil at the bottom of the ditch.

[0217] 6.3 Construction of the water dynamic balance algorithm for the drainage ditch. The dynamic change of the water volume in the drainage ditch satisfies the water continuity equation:

[0218]

[0219] Wherein, V is the volume of water in the drainage ditch; Qin is the water inflow into the drainage ditch; Qout is the water outflow from the drainage ditch; L is the seepage loss; and E is the evaporation loss.

[0220] 6.4 Construction of the water wave propagation algorithm. Under dynamic conditions, the water transport in the drainage ditch can be described by the Saint-Venant equations:

[0221]

[0222] Wherein, h is the water depth; Q is the flow rate; A is the wetted cross-sectional area; g is the acceleration due to gravity; and n is the Manning roughness coefficient.

[0223] 6.5 Canal water entering the agricultural ditch (WU). It is optional whether to enter the agricultural ditch and what proportion enters the agricultural ditch. The calculation formula:

[0224] WF(10 8 m 3 ) = C4 × i

[0225] This method can be used for the evaluation of winter irrigation water in farmland. After winter irrigation water conservation, the water transport path changes from being dominated by the drainage ditch to mainly discharging groundwater into the Yellow River. The existing water transport algorithms cannot accurately describe this change, and there is an urgent need for a scientific method based on accurate evaluation to support the reasonable improvement of winter irrigation water after water conservation. Predictions are made in the Ningxia section of the Yellow River Basin. The overall time of 34 days during the winter irrigation period remains unchanged, and the prediction of water savings is delayed by 1 to 8 days as a whole. The prediction results show that delaying winter irrigation can effectively improve the water transmission efficiency in the diversion canal. Delaying winter irrigation by 1 day, the water saved during the winter irrigation period in the study area is 5.32×10 6 m 3 , the water allocation per hectare of farmland increases by 18 m 3 , and the water diversion efficiency increases by 1.6%; delaying irrigation by 8 days, the water saved during the winter irrigation period in the study area is 42.47×10 6 m 3 , the water allocation per hectare of farmland increases by 143 m 3 , and the water diversion efficiency increases by 12.8%. At the same time, affected by the decrease in temperature, the soil freezing rate increases, which can improve the soil moisture content in the second year.

[0226] It should be understood that for those of ordinary skill in the art, improvements or transformations can be made according to the above description, and all such improvements and transformations should fall within the protection scope of the appended claims of the present invention.

Claims

1. A method for evaluating the water migration process of farmland winter irrigation, characterized in that: The following steps are involved: Step 1: Selection of research area, research time, and validation area; Step 2: Analyze the winter irrigation water migration path in the study area, divide it into four levels: "water diversion channel-farmland surface-farmland underground-drainage ditch", and construct a water migration system; Step 3: Construct the water transport algorithm of the diversion channel; Step 4: Construct farmland surface water transport algorithm; Step 5: Construct farmland groundwater migration algorithm; Step 6: Construct drainage ditch water transport algorithm.

2. The method according to claim 1, characterized in that In the step 2, analyzing the winter irrigation water migration path of the study area includes the following steps: analyzing the water migration path of the water diversion channel; analyzing the farmland surface water migration path; analyzing the farmland groundwater migration path; analyzing the drainage ditch water migration path; constructing a water migration system; and constructing a complete winter irrigation water migration system based on the analyzed structure.

3. The method according to claim 2, characterized in that In step 2, analyzing the migration path of winter irrigation water in the study area includes the following steps: Analysis of the water migration path of the diversion channel: The Yellow River diverts water WDI to the diversion channel Cn, and after evaporation loss ECn and human loss WU, it is diverted to farmland irrigation WF; The migration path of farmland surface water is analyzed as follows: farmland irrigation WF and rainfall P water go to farmland, and then infiltrate into groundwater PSA after farmland water evaporation EF and pumping irrigation PI, and part of the water replenishes the surface RSA; the water content of farmland before irrigation is Wsa, and the water content of farmland after irrigation is Wsb; Analysis of the farmland groundwater migration path: farmland surface water infiltrates to the farmland underground PSA, flows to the drainage ditch RFDi and the Yellow River RFD0 after passing through the farm ditch infiltration IS1, the surface replenishment RSA and the pumping irrigation PI; the groundwater level before irrigation is Wua, and the groundwater level after irrigation is Wub; Analysis of the drainage ditch water migration path: After the groundwater flows to the drainage ditch RFDi Dn, it undergoes evaporation loss EDn and flows into the Yellow River WDR.

4. The method according to claim 1, characterized in that: In the step 3, constructing the water transfer algorithm of the water diversion channel includes: constructing the water balance algorithm of the water diversion channel; constructing the water evaporation algorithm; constructing the water vapor pressure algorithm; and constructing the 40-minute scale algorithm.

5. The method according to claim 4, characterized in that In step 3, constructing the water transport algorithm of the water diversion channel specifically includes: The water balance algorithm of the water diversion channel is constructed; the water diversion channel draws water from the river and reaches the farmland after passing through n-level water diversion channels; the algorithm for the water diversion channel to draw water from the river to the farmland is as follows: WF=WDI-EC n -WU=C n -WU Among them, WF is the amount of water reaching the fields; WDI is the amount of water diverted from the river; EC is the evaporation of the diversion channel; n is the different levels of diversion channels, 1, 2, 3,…, n; WU is the unused water that has not been used in the farmland; C is the retention amount of water in the diversion channels of different levels. The water evaporation algorithm described is constructed; water evaporation is calculated using Dalton's theorem modified by the suitability of the study area: Where E is the saturated water vapor pressure at the water surface temperature, which is 3170 Pa at 25 ° C; e150 is the actual water vapor pressure at a height of 150 cm above the water surface; u 150 It is the wind speed (u1) + flow speed (u2) at 150cm above the water surface, in m / s; The water vapor pressure algorithm is constructed as follows: 1) Calculation of saturated water vapor pressure: Where, t is degrees Celsius; 2) Calculation of actual water vapor pressure: e=Ef Among them, f is relative humidity; relative humidity directly reflects the degree of air saturation; when f = 100%, the air has reached saturation, when it is not saturated, f < 100%, when it is oversaturated, f > 100%; the size of relative humidity is not only related to the water vapor content in the atmosphere, but also decreases with the increase of temperature; when the water vapor pressure remains unchanged, the temperature rises, the saturated water vapor pressure increases, and the relative humidity decreases; The 40-min scale algorithm is constructed; affected by the rotation of the earth, the evaporation trend with temperature as the main influence shows periodic fluctuations of the cosine function; the cosine function is introduced to calculate the 40-min scale water evaporation; the simplified formula is as follows: Among them, EC is the instantaneous evaporation; c0 is the average evaporation, which is controlled by the uniform temperature; A is the water evaporation amplitude, which is controlled by the lowest temperature and the highest temperature; c is the radial frequency of water evaporation; t is the unit time of 40min scale; It is the lag time of water evaporation in response to temperature; the simulation time is from 10 am to 10 am the next day, and 40 minutes is the basic calculation unit.

6. The method according to claim 1, characterized in that In step 4, constructing the farmland surface water migration algorithm includes: constructing the water balance algorithm of the water diversion channel; constructing the PSA algorithm of surface water infiltration into groundwater; constructing the EF algorithm of farmland evapotranspiration; and constructing the RSA algorithm of water replenishment from the groundwater layer to the farmland surface.

7. The method according to claim 1, characterized in that In step 1, the principles for selecting the study area, study time, and verification area include the following: the completeness of the irrigation and drainage system; the representativeness of the study time; Verify the typicality of the area; Feasibility of technology and data support.

8. An evaluation system for the winter irrigation water transport process of farmland, characterized in that , comprising: a processor and a memory for storing a computer program that can be run on the processor; wherein the processor, when running the computer program, executes the steps of the method described in any one of claims 1 to 7.

9. A storage medium having a computer program stored thereon, characterized in that When the computer program is executed by a processor, the steps of any method described in claims 1 to 7 are implemented.

10. A computer program product, comprising a computer program, characterized in that When the computer program is executed by a processor, the steps of the method described in any one of claims 1 to 7 are implemented.

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