Regulation simulation method and simulation device for the influence of open ditch drainage in farmland

Abstract

The present invention discloses a regulation simulation method and a simulation device for the influence of regional open ditch drainage on farmland, including: collecting basic hydrological meteorological and field data of the research area; establishing a water flow model and a crop growth model of the research area; discretizing the water flow model in time and space, constructing a surface water and groundwater data interaction module and defining the module boundary, and calculating the daily cumulative process and yield of above-ground crop biomass in combination with the crop growth model; calibrating and verifying the water flow model and the crop growth model established in step 2; establishing a simulated open ditch drainage model based on the open ditch data and the data of the buildings on the open ditch; simulating the regional water dynamics under the condition of open ditch drainage, and outputting the drainage volumes of each level of open ditches and the drought and waterlogging intensities of each field block; determining the design objective, and adjusting the open ditch parameters, the positions of sluices and weirs, and the regulation scheme to achieve the design objective. The present invention provides a more accurate and efficient way for studying the water dynamics and crop growth simulation under the condition of large-area open ditch layout.

Description

Technical Field

[0001] The present invention belongs to the technical field of agricultural drainage simulation, and particularly relates to a method and device for regulating the influence of regional open ditch drainage on farmland. Background Art

[0002] Drought, waterlogging and salinity disasters are one of the most serious natural disasters in the world, especially posing a serious threat to agricultural production. The increase in extreme drought and waterlogging events affects the growth and development of crops, thus endangering global food production and food security. Controlled drainage is an improvement over the traditional free drainage method. By means of engineering and management measures, the open ditch system in the field is controlled to achieve the reduction of the groundwater level during the waterlogging period, and the groundwater level is raised during the drought period to supplement soil water and reduce the drought stress on crops. According to most production practices, farmland controlled drainage facilities play a positive role in preventing agricultural drought, waterlogging and salinity disasters, promoting the normal growth of crops, rationally utilizing water resources, and promoting economic development. The main controlled drainage methods are open ditches and buried pipes. The focus of the research on open ditch controlled drainage is the engineering layout and regulation scheme of open ditches. The determination of the position, burial depth, spacing, cross-sectional size and outlet weir height of open ditches is the key technology and main task in the design of open ditch drainage systems.

[0003] At present, there are two methods for determining the regional waterlogging regulation method: field experiments and computer simulation. Field experiments are to set different open ditch layouts and regulation methods in the field, and determine the optimal regulation method of open ditches by measuring specific indicators such as drainage volume, groundwater level, crop yield and quality. However, this method is limited by the area of the experimental field and the human and material resources required for the experiment, and can only carry out experiments for specific situations, such as a specific crop, a specific region and a specific drainage method. Moreover, the experimental period is generally long, the cost is high, and the index measurement is complex. Most of the existing computer simulation programs are carried out for ideal or simplified drainage methods and soil parameters, and simulate small-scale and small-number field open ditches, which cannot reflect the whole process of water flow from the field into small ditches, medium ditches and then into large ditches under the condition of the combined layout of large-scale backbone open ditches and field open ditches, nor the situation of soil water and groundwater level in the whole region, and cannot determine the drainage and yield increase effect of the open ditch system regulation in the whole region.

[0004] In order to determine the appropriate regulation water level of open ditches, open ditch control buildings and open ditch regulation schemes, obtain the dynamics of surface water, soil water and groundwater under the regulation of open ditch water level within the regional scope, and ensure the water control and yield increase effect of open ditch regulation, it is necessary to develop a more efficient and accurate simulation method. Summary of the Invention

[0005] The object of the present invention is to provide a regulation and simulation method for the impact of regional open ditch drainage on farmland in view of the deficiencies of the prior art. This method regulates open ditch drainage with the drainage volume of the entire regional open ditch drainage system, the regional waterlogging situation, and the crop effect as the design objectives, so as to effectively ensure the drainage effect under the condition of large-scale open ditch drainage.

[0006] To solve the above technical problems, the present invention adopts the following technical solutions:

[0007] An object of the present invention is to provide a regulation and simulation method for the impact of regional open ditch drainage on farmland, including the following steps:

[0008] Step 1. Collect basic hydrometeorological and field data of the research area;

[0009] Step 2. Based on the basic hydrometeorological and field data collected in Step 1, establish a water flow model and a crop growth model of the research area;

[0010] Step 3. Combine the basic hydrometeorological and field data, discretize the water flow model obtained in Step 2 in time and space, construct an interaction module for surface water and groundwater data and define the module boundary, input the initial groundwater level, soil moisture content, and upper boundary source and sink in the module to simulate groundwater and surface water data, and simulate the daily cumulative process and yield of crop aboveground biomass according to the simulated groundwater and surface water data combined with the crop growth model in Step 2;

[0011] Step 4. Use the measured data to calibrate and verify the water flow model and the crop growth model established in Step 2 in combination with Step 3;

[0012] Step 5. Based on the open ditch data and the data of the buildings on the open ditch, establish a simulated open ditch drainage model;

[0013] Step 6. Use the model in Step 5 to simulate the regional water dynamics under the condition of open ditch drainage, output the drainage volume of each level of open ditch, the drought and waterlogging intensity of each field block, and simulate the crop yield of each field block according to the drainage volume of the open ditch combined with the crop growth model calibrated in Step 4;

[0014] Step 7. Take one or all of the requirements of the maximum crop yield, the lowest drainage volume of each level of open ditch, and the lowest drought and waterlogging intensity of each field block as the design objectives, adjust the open ditch parameters, the position of the sluice and weir, and their regulation schemes, simulate the output variables after each adjustment, that is, the crop yield, the drainage volume, and the drought and waterlogging intensity. According to whether the output variables reach the design objectives, determine the optimal open ditch parameters, the position of the sluice and weir, and their regulation schemes. Otherwise, modify and adjust the open ditch parameters, the position of the sluice and weir, and their regulation schemes for re-simulation until the output variables reach the design objectives.

[0015] Further, the basic hydro-meteorological and field data in Step 1 include, but are not limited to, spatial geographical data, meteorological data, hydrogeological data, soil data, irrigation data, drainage system data, and field management data.

[0016] Further, the water flow models in Step 2 include surface water flow models, open ditch water flow models, soil water flow models, and groundwater flow models.

[0017] Further, the surface water flow model is:

[0018]

[0019] In the formula: Q surf is the surface runoff; p is the daily precipitation; I a is the initial loss before surface waterlogging; S is the maximum possible surface storage after runoff starts;

[0020] The open ditch water flow model is:

[0021]

[0022] In the formula: Q is the flow in the open ditch, m 3 / s; s is the distance in the water flow direction, m; A is the cross-sectional area of the open ditch, m 2 ; B is the water surface width of the open ditch, m; H is the open ditch water level, m; q is the net flow into the open ditch, m 2 / s; α is the flow correction coefficient, dimensionless; g is the acceleration due to gravity, m / s 2 ; S f is the frictional resistance slope; v s is the velocity of q along the water flow direction, m / s;

[0023] The soil water flow model is:

[0024]

[0025] In the formula, θ is the soil volumetric water content, dimensionless; t is the time, d; z is the Z-axis coordinate in the soil numerical direction, with the ground as 0 and upward as the positive direction, cm; S represents the source-sink term; K(h) is the soil unsaturated hydraulic conductivity, which is a function of the soil water potential h and is determined according to the soil water characteristic curve; h is the soil water potential;

[0026] The groundwater flow model is:

[0027]

[0028] In the formula, K is the saturated hydraulic conductivity, m / s; K xx 、K yy 、K zzare the components of the permeability coefficient in the x, y, and z directions, m / s; h is the hydraulic head, m; W is the external source / sink term, 1 / s; S s is the aquifer storage rate, 1 / m; Ω is the simulation domain, m; s1 and s2 are the simulation boundaries; φ is the constant-head boundary, m; ψ is the constant-flow boundary, m / s.

[0029] Furthermore, the crop growth model is:

[0030]

[0031] where: yld is the crop yield at harvest, kg / hm 2 ; HI is the harvest index; Ba is the above-ground biomass of the plant, kg / hm 2 ; i is the serial number of the i-th day; ΔB p is the potential growth of the crop on the i-th day, kg / hm 2 ; f min is the minimum value of the stress factor affecting the crop, f w 、f wd and f t are the drought, waterlogging, and temperature stress factors of the plant, dimensionless; BE is the conversion factor for the crop to convert energy into biomass, (kg / hm 2 ) / (MJ / m 2 ); Par is the solar radiation received by the crop, MJ / m 2 .

[0032] Furthermore, in step 4, the permeability coefficient, specific yield, CN value, permeability coefficient k of the small and large ditches, and roughness of the flow model are calibrated, and the maximum harvest index HI of the crop and the biomass-energy conversion rate of the crop growth model are calibrated.

[0033] Furthermore, in step 5, the open ditch data includes the bottom elevation, spacing, bottom width, side slope coefficient, outlet control degree, and controlled area of each level of open ditch; the data of the buildings on the open ditch includes the location of the hydraulic structures on the open ditch and the building type, width, aperture, bottom elevation, and height.

[0034] Furthermore, according to the groundwater level results calculated by the groundwater module, in step 6, the following formula is used to calculate the cumulative drought and waterlogging intensity ACDWI at each point to evaluate the drought and waterlogging conditions at each point in the region:

[0035]

[0036] where: SEW x is the cumulative depth of groundwater exceeding the standard, which is an index for evaluating crop waterlogging; SEW yThe cumulative depth of groundwater is less than the standard depth, which is an indicator for evaluating crop drought. N is the total number of simulated years. m1 represents the number of days when the actual groundwater depth is less than the standard depth of groundwater for waterlogging. m2 represents the number of days when the actual groundwater depth is greater than the standard depth of groundwater for drought. t is the groundwater depth on day t during the study period; X is the upper limit of the suitable groundwater depth; Y is the lower limit of the suitable groundwater depth; H max The maximum depth of groundwater.

[0037] Another object of the present invention is to provide a device for implementing the above-mentioned method for controlling the impact of regional open ditch drainage on farmland, comprising a basic data acquisition unit, a modeling unit, a calibration and verification unit, a layout unit, a simulation unit, an adjustment unit, an execution unit, and a control unit;

[0038] Basic data acquisition unit, which is used to obtain basic data of the research area;

[0039] a modeling unit, which is in communication with the basic data acquisition unit and establishes a water flow model and a crop growth model for the study area based on the basic data collected by the basic data acquisition unit;

[0040] The calibration and verification unit is connected to the basic data acquisition unit and the modeling unit to calibrate and verify the water flow model and the crop growth model to obtain a calibrated and verified model;

[0041] The layout department, which is connected to the basic data acquisition department and the calibration and verification department, refines the grid in the open ditch drainage area and other areas specified by the model, and determines the reasonable layout of open ditch hydraulic structures, open ditch water level control plan, and field open ditch parameters in the region based on historical open ditch distribution data, and then arranges the open ditch drainage system in the region;

[0042] The simulation unit is connected to the layout unit in communication, simulating regional water dynamics, drought and flood conditions, and crop growth under open ditch drainage conditions, and outputting drainage volume, drought and flood indicators, and crop yields;

[0043] The adjustment unit is connected to the layout unit and the simulation unit, and adjusts the open ditch layout and control parameters according to the design goals and actual regional conditions to achieve the open ditch system design goals;

[0044] The control unit is connected to the basic data acquisition unit, modeling unit, calibration and verification unit, layout unit, simulation unit, and adjustment unit to control their operations.

[0045] Furthermore, it also includes:

[0046] The input and display unit is connected to the basic data acquisition unit, the modeling unit, the calibration and verification unit, the layout unit, the simulation unit, the adjustment unit, and the control unit, and is used to allow the user to input operation instructions and display corresponding information;

[0047] An image generation unit, which is communicatively connected to the layout unit, the simulation unit, the adjustment unit, the input display unit, and the control unit, generates a corresponding open ditch layout diagram according to the open ditch drainage system arranged by the layout unit, generates corresponding change charts of water dynamics, drought and waterlogging indicators, and crop growth processes according to the water dynamics, drought and waterlogging indicators, and crop growth processes simulated by the simulation unit, and generates an adjusted open ditch layout diagram according to the adjustment situation of the adjustment unit; wherein, the input display unit displays the images generated by the image generation unit;

[0048] An execution unit, which is communicatively connected to the layout unit, the simulation unit, the adjustment unit, and the control unit, includes multiple open ditch excavation and renovation robots, and constructs or renovates the open ditch system on the corresponding area according to the open ditch layout parameters and layout methods that reach the design objectives of the open ditch drainage system determined by the adjustment unit;

[0049] In addition, the image generation unit is also communicatively connected to the execution unit, and generates a construction progress diagram according to the on-site layout situation of the execution unit.

[0050] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0051] According to the soil, land cover classification, hydrogeology, open ditch position, cross-section parameters, outlet control parameters, control building position, and control scheme of the region, the present invention simulates the water dynamics and crop growth dynamics of the entire region under the condition of open ditch drainage, reflects the surface water, open ditch water, soil water, and groundwater conditions of the entire region under the condition of large-scale open ditch controlled drainage (including free drainage), and can also determine the drainage volume of the open ditch drainage system of the entire region, the waterlogging status of the region, and the crop effect, making up for the deficiencies in the existing models that only consider field open ditches and do not consider the exchange volume between open ditch water and other parts of the water cycle, providing a new way for regional open ditch drainage simulation, and providing a more accurate and efficient method for studying water dynamics and crop growth simulation under the condition of large-area open ditch layout;

[0052] In addition, the present invention can also generate a regional open ditch layout diagram and a regulation and control scheme that meet the corresponding drainage effect objectives, providing more intuitive technical support for actual open ditch layout and regulation. Construction according to the regional open ditch layout diagram and management according to the regulation and control scheme can effectively ensure the drainage effect under the condition of large-scale open ditch drainage. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 It is a flowchart of the regulation and simulation method for the impact of regional open ditch drainage on farmland provided by the present invention;

[0054] Figure 2Geographical location map of the Anhui Lixin experimental area and irrigation rainfall evaporation data map involved in the embodiments of the present invention; among them, (a) is the location of the Lixin experimental area in Anhui Province, China and Lixin County, (b) is the location of the channels and observation wells in the Lixin experimental area, and (c) is the irrigation rainfall evaporation data map of the Lixin experimental area;

[0055] Figure 3 Graph of the comparison results of the measured and simulated values of the open ditch water level and groundwater level in the Lixin experimental area involved in the embodiments of the present invention; among them, (a) is the comparison graph of the rut ditch water level simulated during the model calibration period and the measured value, (b) is the comparison graph of the rut ditch water level simulated during the model verification period and the measured value, (c) is the comparison graph of the groundwater level simulated during the model calibration period and the measured value, and (d) is the comparison graph of the groundwater level simulated during the model verification period and the measured value;

[0056] Figure 4 Graph of the comparison results of the measured and simulated values of the groundwater in each observation well in the Lixin experimental area involved in the embodiments of the present invention;

[0057] Figure 5 Spatial distribution map of crop yields in the Lixin experimental area involved in the embodiments of the present invention; among them, (a) is wheat; (b) is corn, and (c) is soybean.

[0058] Figure 6 Cumulative drought and waterlogging intensity of each field block in the study area when the small ditch spacing is 250m;

[0059] Figure 7 Different open ditch layout maps of the study area in the Huaibei Plain of Anhui involved in the embodiments of the present invention; among them, (a) small ditch spacing 100m (b) small ditch spacing 250m (c) small ditch spacing 400m. Detailed implementation manners

[0060] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0061] It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other.

[0062] Next, the present invention will be further described in conjunction with specific embodiments, but it is not a limitation of the present invention.

[0063] As Figure 1 shown, the present invention discloses a regulation simulation method for the impact of regional open ditch drainage on farmland, including the following steps:

[0064] Step 1. Collect basic data of the research area, including spatial geographical data, meteorological data, hydrogeological data, soil data, irrigation data, drainage system data, field management data, etc.;

[0065] In this embodiment, the test area is located in Lixin County, Bozhou City, Anhui Province, in the south-central part of the Huaibei Plain, at longitude 116°8′17〞–116°14′37〞 and latitude 33°5′55〞–33°18′19〞. The geographical location of the test area is as Figure 2 (a) and (b) show. It is about 22.1 km long from north to south and about 7.0 km wide from east to west, with an area of 70 km 2 , the surface elevation of the test area is between 28 m and 30 m, the terrain is relatively flat, the strata can be divided into two layers vertically, the average thickness of the upper layer is 6 m, and the main aquifer is about 35 m. The rainfall and evaporation data of the test area are as Figure 2 (c) shows.

[0066] Step 2. Based on the basic hydro-meteorological and field data collected in Step 1, establish a water flow model and a crop growth model for the research area;

[0067] Among them, the water flow model includes a surface water flow model, an open ditch water flow model, a soil water flow model, and a groundwater flow model; in this embodiment, different grid division and refinement methods can be used to perform water volume exchange between surface water and groundwater through the overlapping area to improve the accuracy of the model. The groundwater is simulated using rectangular grids, and can be simulated by conventional encryption of MODFLOW or local encryption of MODFLOW-LGR. Combining the land cover classification results, the surface grid can be divided into any shape (triangle, quadrilateral or polygon, etc.) and converted into a GIS file in shp format and input into the surface water flow model to simulate the surface water runoff generation process. The simulated surface water flow model is:

[0068]

[0069] In the formula: Q surf is the surface runoff, mm; p is the daily precipitation, mm; I a is the initial loss before there is surface water accumulation, mm; S is the maximum possible surface water storage after runoff starts, mm. The initial loss includes all losses before runoff starts, including surface depression storage, vegetation interception, evaporation, and infiltration. The CN value is an empirical parameter that combines soil layer characteristics, surface cover, and initial soil water content information.

[0070] The water flow process after surface water flows into an open ditch is simulated through virtual line elements. Through the line elements of the open ditch, the whole process of field drainage (including rainfall runoff and groundwater seepage) from small field ditches to medium ditches and then to large ditches can be simulated and calculated, realizing the simulation of multi-level open ditch drainage. In this process, the mutual influence between channels at all levels and the mutual exchange between open ditch water and groundwater can be simulated. Among them, the open ditch water flow model is as follows:

[0071]

[0072] In the formula: Q is the flow rate in the open ditch, m 3 / s; s is the distance in the water flow direction, m; A is the cross-sectional area of the open ditch, m 2 ; B is the water surface width of the open ditch, m; H is the water level of the open ditch, m; q is the net flow rate entering the open ditch, m 2 / s; α is the flow rate correction coefficient, dimensionless; g is the acceleration due to gravity, m / s 2 ; S f is the frictional head loss gradient; v s is the velocity of q along the water flow direction, m / s;

[0073] In the calculation of surface water and open ditch water flow, simulating the flow rate of the upper-level open ditch (small ditch or medium ditch) entering the lower-level open ditch (medium ditch or large ditch) can solve the deficiency in the existing drainage system simulation method that cannot reflect the backwater effect of the open ditch outlet water level on the open ditch flow rate, as well as the water replenishment effect of the lower-level open ditch on the upper-level open ditch. When calculating, if the water level of the lower-level open ditch is lower than the water level of the upper-level open ditch, the lower-level open ditch (large ditch or medium ditch) affects the outlet flow rate of the upper-level open ditch (medium ditch, small ditch) through the following formula:

[0074]

[0075] In the formula: Q is the flow rate of the upper-level open ditch entering the lower-level open ditch, m3 / s; σ is the backwater coefficient of the lower-level open ditch on the upper-level open ditch, dimensionless; h is the water depth of the upper-level open ditch, m; m is the side slope coefficient of the upper-level open ditch, dimensionless; b is the bottom width of the upper-level open ditch, m; R is the hydraulic radius of the upper-level open ditch, m; n is the roughness coefficient of the upper-level open ditch, dimensionless; i is the longitudinal slope gradient of the upper-level open ditch, dimensionless; x is the ratio of the height by which the water level of the lower-level open ditch exceeds the outlet elevation of the upper-level open ditch to the water depth of the upper-level open ditch, dimensionless. When the water level of the lower-level open ditch exceeds the water depth of the upper-level open ditch and both are greater than the bottom elevation of the upper-level open ditch, Q is calculated using the following formula:

[0076]

[0077] Where: z1 is the water level of the lower open ditch, m; z2 is the water level of the upper open ditch, m; n is the roughness coefficient of the open ditch, dimensionless; L is half of the length of the upper open ditch, m; R is the hydraulic radius, m; A2 is the cross-sectional area of the upper open ditch at the midpoint, m 2 ; A1 is the cross-sectional area of the upper open ditch at the outlet, m 2 ; A 12 is the mean value of A1 and A2, m 2 .

[0078] The soil water flow model is:

[0079]

[0080] Where, θ is the volumetric water content of the soil, dimensionless; t is the time, d; z is the Z-axis coordinate of the soil numerical direction, with the ground as the 0 point and the upward direction as the positive direction, cm; S represents the source-sink term, which is the root water uptake term in this study, 1 / cm K(h) is the unsaturated hydraulic conductivity of the soil, which is a function of the soil water potential h and is determined according to the soil water characteristic curve; h is the soil water potential;

[0081] The groundwater flow model is:

[0082]

[0083] Where, K is the saturated hydraulic conductivity, m / s; K xx , K yy , K zz are the components of the hydraulic conductivity in the x, y, and z axis directions, m / s; h is the hydraulic head, m; W is the external source-sink term, 1 / s; S s is the aquifer storage rate, 1 / m; Ω is the simulation range, m; s1, s2 are the simulation boundaries; φ is the constant head boundary, m; ψ is the constant flow boundary, m / s.

[0084] The established crop growth model is:

[0085]

[0086] Where: yld is the yield at crop harvest, kg / hm 2 ; HI is the harvest index; Ba is the aboveground biomass of the plant, kg / hm 2 ; i is the serial number of the i-th day; ΔB p is the potential growth amount of the crop on the i-th day, kg / hm 2 ; f min is the minimum value of the stress factor on the crop, f w , f wd and f tThey are the drought, waterlogging and temperature stress factors of plants, dimensionless; BE is the conversion factor for crops to convert energy into biomass, (kg / hm 2 ) / (MJ / m 2 ); Par is the solar radiation obtained by crops, MJ / m 2 .

[0087] Step 3: Combine the basic hydrometeorological and field data, discretize the water flow model obtained in Step 2 in time and space, construct an interaction module for surface water and groundwater data and define the module boundary, input the initial groundwater level, soil moisture content and upper boundary source and sink in the module to simulate the groundwater and surface water data, and calculate the daily cumulative process and yield of crop aboveground biomass according to the simulated groundwater and surface water data combined with the crop growth model in Step 2;

[0088] In this embodiment, the time and space discretization is specifically as follows: In the spatial groundwater simulation, in the horizontal direction, the regional model is divided into 272 rows × 94 columns, a total of 25,568 grids, of which 13,447 are effective grids, and the grid sizes are 100m × 100m, 100m × 50m and 50m × 50m. The vertical simulation depth is 35m, divided into 2 numerical layers. The first layer represents the semi-permeable layer with a thickness of 6m, and the second represents the main aquifer with a thickness of 29m. In the surface water simulation, there are 2,066 plots, 784 small ditch control areas, 182 middle ditch control areas and 5 large ditch control areas in the region. The calibration period is from January 1, 2017 to June 1, 2019, and the verification period is from June 2, 2019 to June 1, 2021, with a time step of 1 day.

[0089] Define the model boundary: The north of the study area is high and the south is low, and the ground slope is about 1:5100; it is relatively flat in the east-west direction. From west to east, there are Xihongsi Gully, Zhonghongsi Gully, Donghongsi Gully, Chezhe Gully and Zhuma Gully respectively. Among them, both Xihongsi Gully and Zhuma Gully originate from farmland about 20 km away from Fumeng New River, and Chezhe Gully originates from Chudian Town about 30 km away from Fumeng New River. The south side of the study area is bounded by Fumeng New River, and the north side is bounded by the starting points of Xihongsi Gully and Zhuma Gully and the junction of Chezhe Gully respectively. Since it is relatively flat in the east-west direction, according to the drainage range controlled by the large ditches, it is considered that the watershed is at the midpoint of the same middle ditch between two adjacent large ditches, and the water flow directions on both sides of the middle ditch are opposite at this point. Then, adjust the above results according to the actual surveyed confluence situation of each large ditch. When calculating the groundwater, set the northern, eastern and western boundaries of the study area as impermeable boundaries, and for the Fumeng New River in the south, since the river channel is deep and large in scale, use the known water head boundary.

[0090] After defining the model boundary, the initial groundwater level, soil moisture content, and upper boundary source and sink are input into the model to simulate daily groundwater and surface water data. According to the simulated groundwater and surface water data, the daily cumulative process and yield of crop aboveground biomass are calculated by combining with the crop growth model in Step 2.

[0091] Step 4. Calibrate and verify the flow model and crop growth model established in Step 2 by using the measured data in combination with the simulation results in Step 3;

[0092] The initial values of soil hydraulic parameters are given according to the measured data for parameter fitting. The values of various soil hydraulic parameters in the calibrated soil water model are given in Table 1. The groundwater module mainly calibrates the hydraulic conductivity and specific yield, and the results can be seen in Table 1. The crop parameters adopt the data of the crop parameter database of EPIC in the United States. Since the data is from the United States, it needs to be corrected and fine-tuned. The parameter data of the calibrated crop growth model can be seen in Table 2. The surface water model mainly uses the SCS runoff generation model, and the main parameter to be calibrated is the CN value. The calibrated data can be seen in Table 3. The open ditch water model mainly calibrates the hydraulic conductivity k and roughness coefficient of small ditches and large ditches, and the calibration results are shown in Table 4. In addition, if the results are not acceptable, the simulation accuracy can be improved by adjusting hydrogeological parameters and the coefficients of calculation source and sink terms, mainly including hydraulic conductivity, specific yield, phreatic evaporation coefficient, etc.

[0093] Table 1 Main parameters of soil water and groundwater models

[0094] Depth (m) 0-0.2 0.2-0.4 0.4-0.8 0.8-6 6-35 <![CDATA[θ r (cm 3 cm -3 )]]> 0.01 0.02 0.01 0.01 0.01 <![CDATA[θ s (cm 3 cm -3 )]]> 0.37 0.4 0.38 0.38 0.38 <![CDATA[α(cm -1 )]]> 0.011 0.011 0.006 0.003 0.003 n 1.58 1.45 1.15 1.1 1.1 <![CDATA[K s (m / d)]]> 2.5 8 10 15 15 Specific yield 0.05 0.05 0.05 0.1 0.1

[0095] Table 2 Main parameters of crop growth model

[0096]

[0097] Table 3 Main parameters of surface water model

[0098] Land use <![CDATA[CN2-A]]> <![CDATA[CN2-B]]> <![CDATA[CN2-C]]> <![CDATA[CN2-D]]> Built-up land 77 86 91 94 Grassland 49 69 79 84 Forest land 45 66 77 83 Crops 62 73 81 84 Bare land 45 66 77 83 Water body 92 92 92 92

[0099] Note: A, B, C, and D in the table refer to four soil water permeability conditions, and CN2 is the CN value under standard moisture conditions

[0100] Table 4 Main parameters of open ditch flow model

[0101]

[0102]

[0103] Figure 3 and Figure 4 are the calibration and verification results. Among them, Figure 3 is the comparison result diagram of the measured and simulated open ditch water levels in the calibration period and verification period in the Lixin test area.Figure 3 (a)–(b) show the variation of the simulated and measured values of the open ditch water level over time during the calibration period and the verification period. Figure 3 (c)–(d) are the scatter plots of the simulated and measured values of the open ditch water level during the calibration period and the verification period; Figure 4 It is a comparison result graph of the measured and simulated values of the groundwater in the Lixin test area, where S1, S2, etc. are Figure 2 the numbers of each observation well in it. The R between the simulated and measured values of the water level during the entire calibration period 2 is 0.57, and RMSE, RMAE, and ME are also less than 0.239, 0.592, and 0.014 respectively; the R of the water level during the model verification period 2 is 0.74, and RMSE, RMAE, and ME are less than 0.327, 0.692, and 0.121 respectively. The variation trends of the simulated and measured values of the groundwater level are basically the same. The errors between the simulated and measured values of the near-ditch points S1, M1, and N1 are relatively small, while those of the far-ditch points such as S10 and N5 are relatively large, but the overall RMSE is less than 0.418. The RMSE of most observation wells is still within 0.5 m, indicating that the model has a certain reliability.

[0104] Step 5. Based on the open ditch data and the data of the buildings on the open ditch, establish a model for simulating open ditch drainage; refine the calculation grid of the surface water in the open ditch layout area, and input the data of the model based on the collected or set open ditch data and the data of the buildings on the open ditch. Among them, the above data include: (1) Open ditch data, including bottom elevation, spacing, bottom width, slope coefficient, outlet control degree, and the controlled area of each level of open ditch, so as to layout the open ditch drainage system in the area. (2) The location of the hydraulic buildings on the open ditch, building types (gate, culvert, bridge, overflow weir, etc.), width, aperture, bottom elevation, height, etc.;

[0105] Locally refine the grid on the cross-section of the groundwater observation well, with the grid size of 50 m×50 m. Provide the open ditch layout data for the model according to the on-site investigation and the open ditch data obtained from Google Earth, including open ditch burial depth, spacing, weir height ratio, cross-section size, controlled area of large, medium, and small ditches, flow direction of large, medium, and small ditches, ditch bottom elevation, open ditch buildings, etc. Establish an open ditch drainage model based on the obtained data, that is, layout the open ditch drainage system in the area. Taking 2017 as the reference year, use the model for simulation. The simulation period starts from January, the initial water head is interpolated from the measured value on January 1, 2017, the time step is 1 day, and the total simulation time is 1613 days.

[0106] Step 6. Use the model in Step 5 to simulate the regional moisture dynamics (including the groundwater level of each grid and the moisture content of each grid's layered soil) during open ditch drainage, and then calculate the drought and waterlogging intensities and crop yields of each field block, and finally output the drainage volumes of each level of open ditch, the drought and waterlogging intensities of each field block, and the crop yields.

[0107] In this example, the drought and waterlogging intensity of the daily groundwater level calculation area of each grid is mainly used, and the stress factors for crop growth are calculated based on the soil moisture content of each grid layer, which is used to calculate the daily increase in crop yield. In this embodiment, the cumulative drought and waterlogging intensity ACDWI is used to evaluate the drought and waterlogging conditions in the area when drought and waterlogging disasters coexist in the area. In addition to crop yield, this index can also reflect the regulation effect of the drainage system on drought and waterlogging, and avoids the deficiency that only the impact of waterlogging disasters is included in the existing indexes. This index is calculated according to the groundwater module in the model of step 2. Specifically, the formula for the cumulative drought and waterlogging intensity ACDWI is:

[0108] ACDWI = (SEW x +SEW y ) / N

[0109]

[0110]

[0111] Where: SEW x is the cumulative groundwater depth exceeding the standard, which is an index for evaluating crop waterlogging, cm·d; SEW y is the cumulative groundwater depth less than the standard, which is an index for evaluating crop drought, cm·d, and N is the total number of simulated years; m1 represents the number of days when the actual groundwater level depth is less than the standard waterlogging groundwater depth, and m2 represents the number of days when the actual groundwater level depth is greater than the standard drought groundwater depth; d t is the groundwater depth on the t-th day within the research period, cm; X is the upper limit of the suitable groundwater depth (for corn and wheat, X is 40 cm and 60 cm respectively, when d t < X, the crop is waterlogged. In the formula, when d t > X, take d t = X, when d t < 0, take d t = 0. In existing research, X = 30 cm is mostly used, and there are also those using X = 50 cm and 60 cm. Y is the lower limit of the suitable groundwater depth (for corn and wheat, Y is 100 cm and 150 cm respectively, when d t > Y, the crop is drought. However, when the groundwater depth is too deep (reaching the groundwater limit depth H max ), the water consumed by soil evaporation and crop transpiration cannot be replenished from the groundwater, so when the groundwater depth d t is greater than H max , take d t = H maxFor a certain crop, the smaller the ACDWI value, the smaller the cumulative drought and flood intensity during the growth period of the crop. Moreover, the crop yields of each field block can be calculated according to the calibrated crop growth model in step 4, and the spatial distributions of the yields and cumulative drought and flood intensities in the study area can be obtained. Figure 5 It is the spatial distribution map of the yields of wheat, corn, and soybeans in each field block in the study area. From Figure 5 it can be seen that most of the farmland in the study area is concentrated in the central and northern regions. Autumn grains are mainly corn, and the planting area of soybeans is very small. The wheat yields are between 0 and 7,200 kg / ha. The areas with decreasing yields are mainly upstream of the control areas of Zhuma Gully and Xihongsi Gully. The closer to Chezhou Gully in the middle, the higher the wheat yields, and the smaller the stress on crop growth. Figure 5 (b) The spatial distribution of the corn yields also shows the same characteristics. Figure 6 It is the cumulative drought and flood intensity of each field block. Since this value is mainly affected by the groundwater depth and has a great relationship with the ground elevation, the spatial characteristics are not obvious. Generally, it shows the characteristics of being large in the middle area and relatively small in the surrounding areas.

[0112] Step 7. Taking one or all of the requirements of the maximum crop yield, the lowest drainage volume of each level of open ditch, and the lowest drought and flood intensity of each field block as the design objectives, adjust the open ditch parameters (depth, spacing, cross-section parameters, outlet weir height), the positions of the sluice weirs, and the regulation schemes, simulate to obtain the output variables (crop yield, drainage volume, and drought and flood intensity) after each adjustment. According to whether the output variables reach the design objectives, determine the optimal open ditch parameters, the positions of the sluice weirs, and their regulation schemes, etc. Otherwise, modify the open ditch parameters, the positions of the sluice weirs, and their regulation schemes and conduct simulations again until the output variables reach the design objectives.

[0113] In this embodiment, calculate the crop yields, drought and flood intensities, and drainage volumes of the region when the small ditch spacings are 100 m, 250 m, and 400 m respectively under the condition that the positions and regulation schemes of the large ditches are the same (see Figure 7 ), so as to obtain the optimal open ditch parameters. In this embodiment, it is the small ditch spacing. Specifically, taking the maximum value of the output values (yield multiplied by price) of wheat, soybeans, and corn as the goal, the average yields and output values of the three crops in each scheme are shown in Table 5. It can be determined that the optimal small ditch spacing in this example is 400 m.

[0114] Table 5 Crop Yields and Total Output Values under the Conditions of Three Simulated Small Ditch Spacings in this Example

[0115] Scheme Wheat yield / 10,000 tons Corn yield / 10,000 tons Soybean yield / 10,000 tons Total output value / 100 million yuan Small ditch spacing 100m 3.86 3.87 146.41 1.85 Small ditch spacing 250m 3.86 3.94 146.11 1.86 Small ditch spacing 400m 3.86 3.95 147.07 1.87

[0116] Note: The marked unit prices of wheat, corn, and soybeans are 2,430 yuan / ton, 2,240 yuan / ton, and 5,950 yuan / ton respectively. The data is from China Grain Information Network (https: / / www.chinagrain.cn / ).

[0117] In this embodiment, a simulation device capable of automatically implementing the above method is also provided, including: a basic data acquisition unit, a modeling unit, a calibration and verification unit, a layout unit, a simulation unit, an adjustment unit, an execution unit, an image generation unit, an input display unit, and a control unit;

[0118] The basic data acquisition unit is used to acquire the basic data of the research area, including spatial geographical data, meteorological data, hydrogeological data, soil data, irrigation data, drainage system data, field management data, etc.;

[0119] The modeling unit is communicatively connected to the basic data acquisition unit. Based on the basic data collected by the basic data acquisition unit, it establishes a water flow model of surface water, open ditch water, soil water, and groundwater and a crop growth model in the research area; then, in combination with the basic data, it establishes a numerical model of water flow movement and crop growth in the research area, discretizes the above water flow model in time and space, defines the model boundary, and inputs the initial soil moisture content, groundwater level, open ditch water level, geological parameters, and upper boundary source and sink;

[0120] The calibration and verification unit is communicatively connected to the basic data acquisition unit and the modeling unit, calibrates and verifies the water flow model and the crop growth model, and obtains the calibrated and verified model;

[0121] The layout unit is communicatively connected to both the basic data acquisition unit and the calibration and verification unit. It refines the grid in the designated open ditch drainage area and other areas of the model, and determines a reasonable layout of open ditch hydraulic structures, an open ditch water level regulation scheme, and field open ditch parameters (depth, spacing, cross-section parameters, outlet weir height) in the area based on the historical data of open ditch distribution. Then, it arranges the open ditch drainage system in the area;

[0122] The simulation unit is communicatively connected to the layout unit, simulates the regional water dynamics, drought and flood conditions, and crop growth conditions under open ditch drainage conditions, and outputs the drainage volume, drought and flood indicators, and crop yields;

[0123] The adjustment unit is communicatively connected to both the layout unit and the simulation unit, and adjusts the open ditch layout and regulation parameters according to the design objectives and the actual situation of the area to achieve the design objectives of the open ditch system;

[0124] The execution unit is communicatively connected to the layout unit, the simulation unit, and the adjustment unit. It includes multiple open ditch excavation and renovation robots, and can build or renovate the open ditch system on-site in the corresponding area according to the open ditch layout parameters and layout methods that meet the design objectives of the open ditch drainage system determined by the adjustment unit;

[0125] An image generation unit, which is communicatively connected to the layout unit, the simulation unit, the adjustment unit, and the execution unit, and is capable of generating a corresponding open ditch layout diagram according to the open ditch drainage system arranged by the layout unit, generating corresponding change charts such as water dynamic and drought and flood indicators according to the water dynamics, drought and flood indicators, and crop growth process simulated by the simulation unit, generating an adjusted open ditch layout diagram according to the adjustment situation of the adjustment unit, and also generating a construction progress diagram according to the on-site layout situation of the execution unit;

[0126] An input display unit, which is communicatively connected to the basic data acquisition unit, the modeling unit, the calibration and verification unit, the layout unit, the simulation unit, the adjustment unit, the execution unit, and the image generation unit, and is used to allow the user to input operation instructions and display corresponding information. For example, the input display unit can display the basic data acquired by the basic data acquisition unit in a list form, display the mathematical models and numerical models of surface water, open ditch water, soil water, groundwater flow, and crop growth constructed by the modeling unit, display the calibration and verification situation of the calibration and verification unit, display all the open ditch drainage system schemes arranged by the layout unit, display the adjustment situation of the adjustment unit and all the schemes that meet the goals determined, and also display the images generated by the image generation unit.

[0127] A control unit, which is communicatively connected to the basic data acquisition unit, the modeling unit, the calibration and verification unit, the layout unit, the simulation unit, the adjustment unit, the execution unit, the image generation unit, and the input display unit, and controls their operations.

[0128] The above are only preferred embodiments of the present invention, and do not limit the implementation manners and protection scope of the present invention. For those skilled in the art, it should be realized that all the equivalent replacements and obvious changes made by using the content of the specification of the present invention should be included in the protection scope of the present invention.

Claims

1. A regulation simulation method for the impact of regional open ditch drainage on farmland, characterized in that, It includes the following steps: Step 1. Collect basic hydrometeorological and field data of the research area; Step 2. Based on the basic hydrometeorological and field data collected in Step 1, establish a water flow model and a crop growth model for the research area; Step 3. Combine the basic hydrometeorological and field data, discretize the water flow model obtained in Step 2 in time and space, construct an interaction module for surface water and groundwater data and define the module boundary, input the initial groundwater level, soil water content and upper boundary source sink in the module to simulate the groundwater and surface water data, and simulate the daily cumulative process and yield of crop aboveground biomass according to the simulated groundwater and surface water data combined with the crop growth model in Step 2; Step 4. Use the measured data to calibrate and verify the water flow model and crop growth model established in Step 2; Step 5. Based on the open ditch data and the data of the buildings on the open ditch, establish an open ditch drainage simulation model; Step 6. Use the model in Step 5 to simulate the regional water dynamics under the condition of open ditch drainage, output the drainage volume of each level of open ditch, the drought and waterlogging intensity of each field block, and simulate the crop yield of each field block according to the drainage volume of the open ditch combined with the crop growth model calibrated in Step 4; Step 7. Take one or all of the requirements of maximum crop yield, minimum drainage volume of each level of open ditch, and minimum drought and waterlogging intensity of each field block as the design goal, adjust the open ditch parameters, the position of the sluice and weir and their regulation schemes, simulate to obtain the output variables after each adjustment, namely crop yield, drainage volume and drought and waterlogging intensity, and determine the optimal open ditch parameters, the position of the sluice and weir and their regulation schemes according to whether the output variables reach the design goal, otherwise modify and adjust the open ditch parameters, the position of the sluice and weir and their regulation schemes for re-simulation until the output variables reach the design goal.

2. The regulation simulation method for the influence of open ditch drainage in the field according to claim 1, wherein, The basic hydrometeorological and field data in Step 1 include but are not limited to spatial geographical data, meteorological data, hydrogeological data, soil data, irrigation data, drainage system data, and field management data.

3. The regulation simulation method for the impact of open ditch drainage in the area on farmland according to claim 1, characterized in that, The water flow models in Step 2 include surface water flow model, open ditch water flow model, soil water flow model and groundwater flow model.

4. The regulation simulation method for the impact of open ditch drainage in the field according to claim 3, characterized in that, [[ID=I0]]The surface water flow model is: Where: Q surf is the surface runoff; p is the precipitation on the day; I a is the initial loss before surface water accumulation; S is the maximum possible surface storage after runoff begins; The open ditch water flow model is: Where: Q is the flow rate in the open channel, m 3 / s; s is the distance in the direction of water flow, m; A is the cross-sectional area of the open channel, m 2 ; B is the water surface width of the open channel, m; H is the water level of the open channel, m; q is the net flow rate entering the open channel, m 2 / s; α is the flow rate correction coefficient, dimensionless; g is the acceleration due to gravity, m / s 2 ; S f is the frictional head loss gradient; v s is the velocity of q in the direction of the water flow, m / s; The soil water flow model is: In the formula, θ is the soil volumetric water content, dimensionless; t is time, d; z is the Z-axis coordinate of the soil numerical direction, with the ground as the 0 point and upward as the positive direction, cm; S represents the source sink term; K(h) is the soil unsaturated hydraulic conductivity, which is a function of the soil water potential h and is determined according to the soil water characteristic curve; h is the soil water potential; The groundwater flow model is: where K is the saturated hydraulic conductivity, m / s; K xx , K yy , K zz are the components of the hydraulic conductivity in the x, y, and z directions, m / s; h is the hydraulic head, m; W is the external source / sink term, 1 / s; S s is the aquifer storage coefficient, 1 / m; Ω is the simulation domain, m; s1, s2 are the simulation boundaries; φ is the constant head boundary, m; ψ is the constant flux boundary, m / s.

5. The regulation simulation method for the impact of regional open ditch drainage on farmland according to claim 1, wherein The crop growth model is: Where: yld is the yield at crop harvest, kg / hm 2 ; HI is the harvest index; Ba is the above-ground biomass of the plant, kg / hm 2 ; i is the serial number of the i-th day; ΔB p is the potential growth of the crop on the i-th day, kg / hm 2 ; f min is the minimum value of the stress factor to which the crop is subjected, f w , f wd and f t are the drought, waterlogging and temperature stress factors of the plant, dimensionless; BE is the conversion factor for the crop to convert energy into biomass, (kg / hm 2 ) / (MJ / m 2 ); Par is the solar radiation received by the crop, MJ / m 2 .

6. The regulation simulation method for the impact of regional open ditch drainage on farmland according to claim 1, characterized in that, In Step 4, calibrate the permeability coefficient, specific yield, CN value, permeability coefficient k of the small ditch and large ditch, and roughness rate of the water flow model, and calibrate the maximum harvest index HI of the crop and the biomass-energy conversion rate of the crop growth model.

7. The regulatory simulation method for the impact of open ditch drainage in the field according to claim 1, characterized in that In Step 5, the open ditch data include bottom elevation, spacing, bottom width, slope coefficient, outlet control degree, and controlled area of each level of open ditch; the data of the buildings on the open ditch include the position of the hydraulic buildings on the open ditch and the building type, width, aperture, bottom elevation, and height.

8. The regulation simulation method for the influence of regional open ditch drainage on farmland according to claim 1, characterized in that, According to the groundwater level results calculated by the groundwater module, in step 6, the cumulative drought and flood intensity ACDWI of each point is calculated by the following formula to evaluate the drought and flood conditions of each point in the region: where: SEW x is the cumulative depth of groundwater above the standard, which is an index for evaluating waterlogging of crops; SEW y is the cumulative depth of groundwater less than the standard, which is an index for evaluating drought of crops; N is the total number of years simulated; m1 represents the number of days when the actual groundwater level depth is less than the standard waterlogging groundwater depth, and m2 represents the number of days when the actual groundwater level depth is greater than the standard drought groundwater depth; d t is the groundwater depth on the t-th day within the study period; X is the upper limit of the suitable groundwater depth; Y is the lower limit of the suitable groundwater depth; H max is the critical groundwater depth.

9. A simulation device for implementing a simulation method for regulating the impact of open ditch drainage in the area described in any one of claims 1-8 on farmland, characterized in that, It includes a basic data acquisition unit, a modeling unit, a calibration and verification unit, a layout unit, a simulation unit, an adjustment unit, an execution unit, and a control unit; The basic data acquisition unit is used to acquire the basic data of the research area; The modeling unit is communicatively connected to the basic data acquisition unit and, based on the basic data collected by the basic data acquisition unit, establishes a water flow model and a crop growth model for the research area; The calibration and verification unit is communicatively connected to the basic data acquisition unit and the modeling unit, calibrates and verifies the water flow model and the crop growth model, and obtains the calibrated and verified models; The layout unit is communicatively connected to both the basic data acquisition unit and the calibration and verification unit, refines the grid in the specified open ditch drainage area and other areas of the model, and determines a reasonable layout of open ditch hydraulic structures, an open ditch water level regulation scheme, and field open ditch parameters in the region based on historical open ditch distribution data, and then arranges an open ditch drainage system in the region; The simulation unit is communicatively connected to the layout unit, simulates the regional water dynamics, drought and flood conditions, and crop growth under open ditch drainage conditions, and outputs the drainage volume, drought and flood indicators, and crop yields; The adjustment unit is communicatively connected to both the layout unit and the simulation unit, and adjusts the open ditch layout and regulation parameters according to the design objectives and the actual situation of the region to achieve the design objectives of the open ditch system; The control unit is communicatively connected to the basic data acquisition unit, the modeling unit, the calibration and verification unit, the layout unit, the simulation unit, and the adjustment unit, and controls their operations.

10. The simulation device of the regulation simulation method for the impact of regional open ditch drainage on farmland according to claim 9, characterized in that It also includes: The input and display unit is communicatively connected to the basic data acquisition unit, the modeling unit, the calibration and verification unit, the layout unit, the simulation unit, the adjustment unit, and the control unit, and is used to allow the user to input operation instructions and display corresponding information; The image generation unit is communicatively connected to the layout unit, the simulation unit, the adjustment unit, the input and display unit, and the control unit. It generates a corresponding open ditch layout diagram according to the open ditch drainage system arranged by the layout unit, generates a corresponding chart of changes in water dynamics and drought and flood indicators according to the water dynamics, drought and flood indicators, and crop growth process simulated by the simulation unit, and generates an adjusted open ditch layout diagram according to the adjustment situation of the adjustment unit; among them, the input and display unit displays the images generated by the image generation unit; The execution unit is communicatively connected to the layout unit, the simulation unit, the adjustment unit, and the control unit, and includes multiple open ditch excavation and renovation robots, and constructs or renovates the open ditch system on-site in the corresponding region according to the open ditch layout parameters and layout methods that achieve the design objectives of the open ditch drainage system determined by the adjustment unit; In addition, the image generation unit is also communicatively connected to the execution unit and generates a construction progress diagram according to the on-site layout situation of the execution unit.

Images