A method for simulating slope hydrological processes

Abstract

The present application provides a method for calculating slope hydrological processes, which belongs to the field of hydrological numerical simulation calculations. The method includes: receiving basic data of the target area; setting the upstream and downstream connection relationship of the slope cells; calculating the moisture interaction process between the vegetation layer, surface layer, unsaturated soil layer and saturated soil layer of each slope cell; calculating the top water storage of the slope cell and the overflow process between cells; correcting the model parameters according to the soil moisture monitoring data to obtain the final time series of the slope soil moisture. The slope hydrological process calculation method proposed in this application can effectively overcome the expression limitations of the traditional surface water-groundwater model when simulating the special green space construction of slope cells, while supporting the calculation of slope hydrological processes with high spatial resolution and high temporal resolution, significantly improving the accuracy and efficiency of the calculation results.

Description

Technical Field

[0001] The present application relates to a slope hydrological process simulation method, which belongs to the field of hydrological numerical simulation calculation. Background Art

[0002] Slope greening is a common greening measure in mountainous plateau cities. Due to the significant elevation differences in mountainous cities, urban roads are often built along steep slopes. To ensure both aesthetically pleasing and safe slopes, closely connected fish-scale pits are often constructed on the existing slopes. These pits are rectangular or other shapes (e.g., 3m x 3m x 0.2m in length, width, and depth). They are framed by concrete frames, secured to the rock layer at the base of the slope using rebar and other means. These interconnected structures cover the entire slope, connecting to drainage channels at their base to collect excess runoff. The bottoms of the fish-scale pits are not interconnected; overflow flows from their tops into downstream pits. Each pit is filled with soil and planted with turf or shrubs, achieving both slope greening and stability. Due to the thin soil layer and the lack of soil and water conservation capacity, these artificially constructed slope greening areas require irrigation, consuming significant amounts of water resources.

[0003] A healthy water cycle is an advanced concept in urban water resource management. Its core is to meet the needs of different water users in the city through differentiated water supply. In this process, wastewater generated by high-quality water users is recycled and reused to meet the water needs of low-quality water users. Specifically, the recycled water generated by urban domestic water use, after being treated at a sewage treatment plant, can be used to meet the irrigation needs of slope green spaces. Because different slope green spaces have different soil and hydrogeological conditions, their irrigation needs also vary. It is necessary to analyze the soil moisture conditions of the fish scale pits according to local conditions and develop a refined irrigation plan to maximize water conservation and avoid waste.

[0004] Traditional soil moisture simulation models often operate at a large computational scale, making it difficult to conduct detailed modeling and analysis of small-scale research units like fish scale pits. For example, within a one-square-kilometer study area, there may be hundreds of thousands of fish scale pits, far exceeding the modeling and computational limits of conventional hydrological models. Therefore, an analytical method is needed that can simultaneously account for detailed hydrological processes within fish scale pits and quantitatively simulate slope green spaces formed by large-scale fish scale pits, thereby providing support for decision-making in precision irrigation. Utility Model Content

[0005] In view of this, this application provides a slope hydrological process simulation method with high granularity and fast calculation speed. The specific technical solution is as follows:

[0006] Step 1: Receive basic data of the target area, including slope cell spatial structure information, digital elevation data, soil data of the slope area, slope vegetation data and meteorological data;

[0007] Step 2: Each slope cell is recorded as an independent model calculation unit, and the upstream and downstream connection relationship of each calculation unit is determined based on the mutual position relationship and elevation data of the cells;

[0008] Step 3: Calculate the water interaction process between the vegetation layer, surface layer, unsaturated soil layer and saturated soil layer of each slope cell;

[0009] Step 4: Calculate the top water storage of the slope cells and the overflow process between cells;

[0010] Step 5: Correct the model parameters according to the soil moisture monitoring data to obtain the final time series of slope soil moisture.

[0011] Through the above technical solution, it is possible to carry out detailed simulation of the hydrological process within the slope cells (fish scale pits), obtain the time series of soil moisture changes within the cells, and determine the irrigation water storage capacity of the cells, thereby guiding the formulation of detailed irrigation plans, providing guidance for maximizing the conservation of recycled water, and promoting the efficient operation of the city's healthy water circulation system.

[0012] Preferably, the basic data of the target area is received, specifically including slope cell spatial structure information, digital elevation data, soil data of the slope area, slope vegetation data, and meteorological data. The cell spatial structure data can be obtained by on-site measurement or through slope design or construction drawing information, including the number of each slope cell, the depth of the cement baffle of each cell, the soil thickness of each cell, and the thickness of the air layer above each cell. The digital elevation data of the slope area can be obtained by on-site measurement or by lidar measurement, and the soil data of the slope area can be obtained by on-site sampling and then measurement. The vegetation type and coverage area in the slope area vegetation data can be obtained by planting planning or remote sensing image interpretation, and the leaf area index of the vegetation can be measured by instruments or estimated based on the vegetation type.

[0013] Preferably, the upstream and downstream connection relationship between the calculation units is set according to the relative position relationship between the elevation data and the cells, specifically including confirming the upstream and downstream relationship of the slope cells through on-site observation, and also taking the side with the highest elevation as the top boundary of the slope based on the elevation data, and the slope cells near the top boundary of the slope as the upstream cells, and then setting the downstream cells in sequence in the longitudinal direction until the drainage ditch at the bottom.

[0014] Preferably, the calculation of the water interaction process between the vegetation layer, surface layer, unsaturated soil layer, and saturated soil layer of each slope cell specifically includes calculating the rainfall interception process, leaf and soil surface evapotranspiration process, vegetation transpiration process, surface water infiltration process, unsaturated layer change process and infiltration process, soil moisture change process, and vegetation water extraction process within each cell.

[0015] 1) Rainfall interception process: The calculation of rainfall interception process includes leaf interception and through-flow precipitation, in which the leaf interception is affected by the maximum water capacity of vegetation (ψ 0max ) and ψ 0max The calculation formula is:

[0016] ψ 0max =K L ×LAI

[0017] Where LAI is the leaf area index, K L Empirical constant.

[0018] The calculation formula for leaf surface interception is:

[0019]

[0020] Among them, ψ0 is the leaf interception amount, P is the rainfall, ET canopy is the evaporation intercepted by leaves, and TF is the throughfall.

[0021] The calculation formula for throughfall (TF) is:

[0022] TF=kexp[b(ψ0 / ψ 0max )]0≤ψ0<ψ 0max

[0023] =kexp[b]0<ψ 0max ≤ψ0

[0024] Where b is the drainage coefficient (dimensionless) and k is expressed in L / T. The value of b is usually between 3.0 and 4.6, and k is usually k = 3.91 × 10 -5 ψ0(mm / min).

[0025] 2) Leaf evaporation process: The calculation formula for the leaf evaporation process is:

[0026]

[0027] Where Δ is the slope of the saturated vapor pressure curve at temperature T (°C), R n is the net radiation of vegetation surface (MJ m - 2 day-1 ), G is the soil heat flux (MJ m -2 day -1 ), ρ a is the atmospheric density (kg / m3), C p is the specific heat of air (MJ kg -1 ℃ -1 ), e s and e a are saturated vapor pressure and actual vapor pressure (kPa), r a is the aerodynamic drag (sm -1 ), γ is the temperature constant (kPa℃ -1 ). δ r is the area ratio of wet vegetation.

[0028] 3) Soil surface evapotranspiration process: The calculation formula for soil surface evapotranspiration is:

[0029]

[0030] Among them, βs reflects the effect of soil surface saturation on surface evaporation, vFrac is the vegetation coverage ratio, θ fl =0.75θ sat is the field water capacity, θ sat is the saturated soil moisture content, θ g The moisture content of the soil surface.

[0031] 4) Vegetation transpiration: The calculation formula for vegetation transpiration by extracting water from soil moisture is:

[0032]

[0033]

[0034] R sc =R s (1-exp(-αLAI))

[0035] η s =1-0.0016(298.0-T a ) 2

[0036] Among them, r s is the stomatal resistance of vegetation (sm -1 ), R of trees s ref The value is usually 30Wm -2 , grassland and crop R s ref The value is usually 100Wm -2 , β sFor agricultural land and shrubland, it is the saturation of the surface soil; for forest, it is the saturation of the unsaturated soil below the surface soil, which is mainly determined by the root depth, η s It reflects that when the temperature is very high or very low, the transpiration of vegetation is weakened. s ref The value is usually 30Wm -2 , r max and r min are the maximum and minimum pore resistance, respectively, where r max Usually 5000sm -1 .

[0037] 5) Surface water infiltration process: The surface water infiltration process is mainly determined by the hydraulic difference between surface water and surface soil water. The calculation formula is:

[0038]

[0039] Where, ψ2 is the surface water level (m), z is the surface elevation (m), ψ3 is the surface soil head (m), K(ψ3) is the hydraulic conductivity (L / T), z u is the topsoil elevation (m), d is the distance between surface water and topsoil (m), K s is the saturated hydraulic conductivity (L / T), α[L -1 ] and n are Van Genuchten parameters.

[0040] 6) Underground horizontal flow process: The horizontal flow of groundwater is Darcy flow, which is mainly determined by the hydraulic conductivity and the hydraulic gradient between adjacent grids. The calculation formula is:

[0041]

[0042] Among them, ψ 4i and ψ 4j is the groundwater head between adjacent grids i and j (m), z bi and z bj is the elevation of adjacent grids i and j (m), d ij is the distance between adjacent grids i and j.

[0043] 7) Unsaturated Layer Change / Infiltration: The unsaturated layer is the portion above the groundwater level and the soil surface. Because groundwater is replenished by water infiltrating from the soil surface, the groundwater level constantly changes, causing the depth and saturation of the unsaturated layer to change over time. The calculation of the saturation of the unsaturated layer is similar to that in 5), accounting for water infiltrating from the soil surface and groundwater rising due to capillary action. The direction of these flows changes with the interaction of rainfall events and evaporation. The specific calculation formula is as follows:

[0044]

[0045] Where ReI is the amount of water infiltrating from the surface soil to the unsaturated layer, and Re is the amount of water infiltrating from the unsaturated layer to the groundwater. Depending on the hydraulic head gradient between these layers, the flow direction may reverse, for example, if groundwater transfers water to the overlying unsaturated layer through capillary action. Therefore, in actual calculations, this formula determines the flow direction and hydraulic conductivity value based on the actual hydraulic head gradient.

[0046] 8) Vegetation growth water use process: The process by which vegetation extracts water from the soil to meet its growth needs is calculated as follows:

[0047]

[0048] Among them, T i,j is the transpiration rate (m / h) in the model grid numbered (i, j), S wi,j is the saturation of the soil in the model grid numbered (i, j), T is the actual transpiration, β(z i,j ) is the root distribution in the (i, j) model grid, and p is an empirical parameter.

[0049] 9) Soil moisture change process: The calculation method of soil moisture change process is based on Richard equation:

[0050]

[0051] Where h is the total water head of the underground part (m), ψ is the pressure head (m), and c(ψ) is the specific water capacity (m -1 ), S s is the specific capacity (m -1 ), S w is the saturation, K(ψ) is the hydraulic conductivity based on the pressure head (m / h), q s is a source or sink term. The hydraulic conductivity based on pressure head and soil moisture are calculated according to the van Genuchten formula:

[0052]

[0053] Among them, K s is the saturated hydraulic conductivity (m / h), θ r is the residual water content, θ s is the saturated water content, α and n are the van Genuchten parameters.

[0054] Preferably, the calculation of the top water storage of the slope cell and the overflow process between cells specifically includes comparing the calculated cell top water storage with the air layer thickness. When the water storage depth is greater than the air layer thickness, the excess water overflows from the cell to the adjacent longitudinal downstream cell. The overflow process is based on the Saint-Venant equation of dynamic waves or diffusion waves, and the vertical direction is approximately completely mixed. The specific calculation formula is:

[0055]

[0056] in, is the gradient of the surface water head in the direction of maximum slope. At the same time, the water head gradient needs to be calculated between all adjacent grids to determine the water flow value in each direction.

[0057] Preferably, the model parameters are corrected according to the soil moisture monitoring data to obtain the final time series of the slope soil moisture, specifically including: in the slope cells equipped with soil moisture monitoring, the relevant parameters of the rainfall interception process, the evapotranspiration process of the leaf surface and the soil surface, the vegetation transpiration process, the surface water infiltration process, the unsaturated layer change process / infiltration process, the vegetation water extraction process, etc. are adjusted until the soil moisture time series calculated by the model is within the error range compared with the monitored value, and the adjusted parameters are applied to all cells. At this time, the model simulation result is the soil moisture time series of each slope cell.

[0058] In summary, this application has at least the following four beneficial technical effects:

[0059] 1. The slope hydrological process simulation framework proposed in this application can perform numerical simulation analysis on any number of slope cells without being restricted by the number of cells.

[0060] 2. The slope hydrological process simulation framework proposed in this application can solve the hydrological process within the slope at a high computing speed, which can meet the timeliness requirements of online deployment.

[0061] 3. The various hydrological processes in the slope hydrological process simulation framework proposed in this application are coupled with each other and can be flexibly adjusted according to the structure of different slope cells, with strong adaptability.

[0062] 4. The calculation results of the slope hydrological process simulation framework proposed in this application can be directly used as a reference for slope green space irrigation. When the soil moisture content of the slope cell is lower than a certain value, irrigation is started, and irrigation is stopped when the soil moisture content returns to a range suitable for vegetation growth in the cell. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] Figure 1 This is the overall technical roadmap of the slope hydrological process simulation method in this invention.

[0064] Figure 2 This is the calculation flow chart of the hydrological process within the cell

[0065] Figure 3 This is the calculation flow chart of the overflow process between cells

[0066] Figure 4 This is an example of the calculation results of the cell soil moisture time series DETAILED DESCRIPTION

[0067] The following will provide a clear and complete description of the technical solutions in the examples of the present invention, in conjunction with the accompanying drawings. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0068] Example

[0069] refer to Figure 1 , a simulation method of slope hydrological process, mainly including the following steps:

[0070] S001: Receive basic data for the target area. Basic data includes slope cell spatial structure information, digital elevation data, slope area soil data, slope vegetation data, and meteorological data. Cell spatial structure data can be obtained through on-site measurement or from slope design or construction drawing information, and includes the number of slope cells, the depth of the cement baffle in each cell, the soil thickness in each cell, and the thickness of the air layer above each cell. Digital elevation data for the slope area can be obtained through on-site measurement or lidar measurement, and soil data for the slope area can be obtained through on-site sampling and subsequent measurement. Vegetation type and coverage in slope area vegetation data can be obtained through planting planning or remote sensing image interpretation. Leaf area index can be measured using instruments or estimated based on vegetation type.

[0071] S002: Each slope cell is recorded as an independent model calculation unit, and the upstream and downstream relationship of each model calculation unit is determined based on the mutual position relationship of the cells and the elevation data. This part can confirm the upstream and downstream relationship of the slope cells through on-site observation, or based on the elevation data, the side with the highest elevation can be used as the top boundary of the slope, and the slope cells near the top boundary of the slope are recorded as the upstream cells. Then, the downstream cells are set in sequence in the longitudinal direction until the drainage channel at the bottom.

[0072] S003: Set the spatial structural characteristic attributes of the calculated cell according to the spatial result information of each cell; this step specifically sets the cell area, soil layer thickness, air layer thickness, and cell slope information, among which the cell area, soil layer thickness, and air layer thickness can be directly measured.

[0073] S004: Set the hydrological characteristics of each calculation cell based on its vegetation type data, soil data, elevation data, and meteorological data. Vegetation type and soil data can be obtained through direct measurement. Cell slope can be calculated from DEM data using common GIS software. Meteorological data can be obtained by obtaining data from nearby weather stations to obtain rainfall, temperature, and humidity information.

[0074] S005: Construct a module for calculating the water interaction between the vegetation layer, surface layer, unsaturated soil layer and groundwater layer; this part includes the rainfall interception process, leaf and soil surface evapotranspiration process, vegetation transpiration process, surface water infiltration process, unsaturated layer change process / infiltration process, and soil moisture change process.

[0075] S006: Construct a calculation module for the water storage process of the slope cell and the overflow process of the upstream cell overflowing to the downstream cell; this process first needs to obtain the slope surface runoff calculated by the water interaction calculation process module between the vegetation layer, surface layer, unsaturated soil layer and groundwater layer, and then compare the surface runoff with the volume of the air layer. If the volume of the air layer is larger than the surface runoff, no overflow occurs and all surface runoff is stored in the cell. If the volume of the cell's air layer is smaller than the surface runoff, the excess runoff flows to the downstream cell as overflow, and the temporary water storage volume in the cell is equal to the volume of the cell's air layer.

[0076] S007: Bring the set calculation cell information into the calculation module to complete the construction of the slope model; in this step, the above calculation process is first integrated into a complete calculation framework, and then the cell information is brought into the model to complete the construction of the framework.

[0077] S008: Correct the slope cell model according to the soil moisture monitoring data, and finally obtain the time series of slope model simulation.

[0078] Among them, such as Figure 2 As shown in Figure 2, the calculation of the hydrological process within the slope cell mainly includes the following steps:

[0079] S501: Rainfall interception process: Calculate the leaf interception water volume and the throughfall precipitation volume respectively. The throughfall precipitation volume is the effective precipitation reaching the cell surface.

[0080] S502: Leaf evapotranspiration process: Calculate leaf evaporation based on air pressure, radiation, atmospheric density, specific heat of air, aerodynamic drag, temperature constant, and the area ratio of wet vegetation in the cell.

[0081] S503: Soil surface evaporation process: Calculate the soil surface evaporation based on the vegetation coverage ratio of the soil surface in the cell, the soil surface water saturation, the field water holding capacity of the cell soil and the saturated water content.

[0082] S504: Vegetation transpiration process: Combined with the vegetation type in the cell, select appropriate stomatal resistance parameters, parameters affecting stomatal resistance by temperature, and surface soil saturation to calculate vegetation transpiration.

[0083] S505: Surface water infiltration process: Calculate the surface water infiltration rate within the cell based on the water level, elevation, soil hydraulic conductivity, etc. of the cell.

[0084] S506: Underground horizontal flow process: Calculate the underground horizontal flow between adjacent grids based on the cell elevation, the spacing between adjacent grids, and the groundwater head of the grids.

[0085] S507: Unsaturated layer changes and infiltration process: The dynamic changes of the unsaturated layer in the cell are calculated by combining the amount of infiltrating water in the cell during rainfall and the amount of groundwater that reaches the upper layer through capillary action for evaporation during non-rainfall periods.

[0086] Among them, such as Figure 3 As shown, the overflow process between cells is calculated. The main steps include: first, obtaining the slope surface runoff volume calculated by the water interaction calculation process module between the vegetation layer, surface layer, unsaturated soil layer, and groundwater layer. Then, the surface runoff volume is compared with the air layer volume. If the air layer volume is greater than the surface runoff volume, no overflow occurs, and all surface runoff is stored in the cell. If the air layer volume of a cell is less than the surface runoff volume, the excess runoff flows as overflow to the downstream cell. The temporary water storage volume in the cell is equal to the cell's air layer volume. The surface water flow process is calculated based on the Saint-Venant equation based on the dynamic wave or diffusion wave approximation, in which the vertical state is approximately completely mixed.

[0087] Specifically, the comparison between the time series of soil moisture content changes in the cell calculated by this method and the observed values ​​is as follows: Figure 4 shown.

Claims

1. A slope hydrological process simulation method, characterized in that: The method comprises: Step 1: Receive basic data of the target area, including slope cell spatial structure information, digital elevation data, soil data of the slope area, slope vegetation data and meteorological data; Step 2: Each slope cell is recorded as an independent model calculation unit, and the upstream and downstream connection relationship of each calculation unit is determined based on the mutual position relationship and elevation data of the cells; Step 3: Calculate the water interaction process between the vegetation layer, surface layer, unsaturated soil layer and saturated soil layer of each slope cell; Step 4: Calculate the top water storage of the slope cells and the overflow process between cells; Step 5: Correct the model parameters according to the soil moisture monitoring data to obtain the final time series of slope soil moisture.

2. The method according to claim 1, wherein The spatial structure information of the slope cells in step 1 includes the engineering design and construction drawings or engineering survey drawings of the slope; the slope soil data includes the soil type, soil porosity, soil saturated hydraulic conductivity and soil moisture of the slope; and the slope vegetation data includes the vegetation type and vegetation leaf area index results.

3. The method according to claim 1, wherein Each slope cell in step 2 is a model calculation unit. There is no lateral interaction of water quantity and water quality between two adjacent slope cells at the same elevation in the horizontal direction of the slope. Only the cells in the vertical direction of the slope have a longitudinal upstream and downstream connection relationship. The cell with a higher elevation is upstream of the adjacent cell with a lower elevation, and the cell with the lowest elevation is connected to the drainage channel at the bottom of the slope.

4. The method according to claim 1, wherein In step three, the moisture interaction process between the vegetation layer, surface layer, unsaturated soil layer and saturated soil layer of each slope cell is calculated, specifically including the calculation of the rainfall interception process, leaf and soil surface evapotranspiration process, vegetation transpiration process, surface water infiltration process, unsaturated layer change process and infiltration process, and vegetation water extraction process in each cell, and finally the time series of the soil moisture change process in the cell is obtained.

5. The method according to claim 1, wherein The calculation process of the water storage at the top of the slope cell and the overflow between cells in step 4 specifically includes using the air layer at the top of the cell as the storage space. After the air layer is filled with water, it overflows from the upstream cell to the downstream cell in the form of a dynamic wave or a diffusion wave, enters the storage space of the downstream cell, and so on, until it reaches the drainage channel at the bottom of the slope.

6. The method according to claim 1, wherein In step five, the model parameters are corrected according to the soil moisture monitoring data to obtain the final time series of the slope soil moisture. Specifically, the calculated slope cell soil moisture data is compared with the monitoring data, and the parameters are adjusted based on the error until the error is within a reasonable range. At this time, the corresponding slope cell soil moisture time series is the final calculation result.

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