River black and odorous early warning method based on urban rainfall runoff pollution load simulation

Abstract

The invention relates to a river channel black and odorous early warning method based on urban rainfall runoff pollution load capacity simulation, which comprises the following steps: selecting an urban small watershed river reach needing river channel black and odorous early warning as a target river reach, and collecting rainfall runoff data generated by session rainfall corresponding to n sessions of black and odorous water in the target river reach; determining core pollutants in the rainfall runoff, and calculating a critical urban rainfall runoff core pollutant load index giving out river black and odorous phenomenon early warning; establishing a basic geographic scene of the model; the system reaches a water level balance state after water distribution; updating the non-point source pollution load and concentration of each cell in a single time step; calculating the transmission process of runoff and non-point source pollution in the urban rainwater pipe network; and when rainfall occurs in the target river reach, early warning of the black and odorous river channel is performed. According to the invention, the early warning accuracy is improved.

Description

Technical Field

[0001] The invention relates to a method for early warning of black and smelly river channels based on simulation of urban rainfall runoff pollution load, which is suitable for early warning of black and smelly phenomena that may occur in urban rivers after rainfall, and belongs to the technical field of black and smelly water treatment. Background Art

[0002] As point source pollution has been effectively controlled, the black and smelly phenomenon of urban rivers has been effectively curbed. However, the impervious area of ​​the city continues to expand, and non-point source pollution caused by rainfall runoff erosion and confluence has become the main reason for the decline in urban water environment quality.

[0003] The key to accurately predicting whether a rainfall will cause a river to become black and smelly is to simulate the pollution load of non-point source pollution generated after rainfall through a model. The non-point source pollution model can quantitatively simulate the migration and transformation process of pollutants. The existing urban non-point source pollution model uses sub-catchment areas as the calculation unit for surface runoff simulation, ignoring the runoff process within the sub-catchment area, resulting in large deviations in the simulation results, and thus being unable to accurately predict whether rainfall will cause a river to become black and smelly. Summary of the invention

[0004] In order to solve the above problems, the present invention discloses a method for early warning of river blackness and odor based on simulation of urban rainfall runoff pollution load, which simulates the urban rainfall runoff pollution process based on cellular automata, thereby improving the large deviation caused by ignoring the internal confluence process of the sub-catchment area in the existing urban non-point source pollution model, and realizing early warning of river blackness and odor based on accurate calculation of urban rainfall runoff pollution load. The specific technical scheme is as follows:

[0005] A method for early warning of river blackness and odor based on simulation of urban rainfall runoff pollution load, comprising the following steps:

[0006] Step (1): Select a small urban watershed river section that needs to be warned of river black and odor as the target river section, collect rainfall runoff data generated by n rainfall events corresponding to black and odorous water bodies in the target river section, where n is an integer ≥ 5, and the rainfall runoff data includes the concentration and total flow of each pollutant in the rainfall runoff; determine the location of the rainwater outlet in the watershed of the target river section based on the pipe network data and field survey, and collect rainfall runoff data of the rainfall events corresponding to the n black and odorous events at the rainwater outlet;

[0007] Step (2): Perform principal component analysis on the rainfall runoff data generated by the n rainfalls corresponding to the black and odorous water bodies in step (1) to obtain the core pollutants in the rainfall runoff, and calculate the average pollution load of the rainfall runoff data generated by the n rainfalls corresponding to the black and odorous water bodies of the screened core pollutants, which is recorded as That is, the critical urban rainfall runoff core pollutant load index for issuing warnings of black and smelly river phenomena;

[0008] Step (3): determine the water collection range of the rainwater outlet as the study area of ​​urban rainfall runoff pollution, obtain the land use type, digital elevation data (DEM) and rainfall changing over time of the study area, and set a cellular space matching the raster data accordingly. The cellular space includes cell size, cell shape and boundary cells, set the running time step of the urban rainfall runoff pollution load accounting model based on cellular automata, and establish the basic geographical scene of the urban rainfall runoff pollution load accounting model based on cellular automata; the cellular space is the geographical space of the study area, that is, the water collection range of the rainwater outlet, which is composed of cells; the cell shape is a square grid, and after the study area is rasterized, each grid corresponds to a cell; the rainfall data of the study area is obtained by measuring with a rain gauge or through a meteorological station, and the rainfall data is spatially interpolated using ArcGIS software to obtain the raster surface of the rainfall data, that is, the rainfall data of each cell at different times is obtained;

[0009] Step (4): According to the principle of conservation of mass, the net rain depth of each cell is calculated through rainfall, vegetation interception rainfall, infiltration and depression storage. The water flows in multiple directions downstream. The water level status of the central cell and the neighboring cells is considered as a whole. The minimum difference method commonly used in the multi-flow method is used to preliminarily calculate the water distribution, so that the system reaches a state of water level balance after water distribution. On the basis of the flow calculated by the minimum difference method, the Manning formula is used to correct the flow;

[0010] Step (5): Use the exponential function washoff model to calculate the non-point source pollution washoff load in each cell, use the saturated function accumulation model to calculate and simulate the initial dry period surface pollutant accumulation, and comprehensively consider the cleaning management measures and runoff washoff. The pollutants generated by the washoff are transmitted and exchanged between each neighboring cell along the runoff transmission direction. The net input of the non-point source pollution load of each cell is calculated. After comprehensively considering the non-point source pollution loss caused by infiltration, the non-point source pollution load and concentration of each cell can be updated within a single time step;

[0011] Step (6): Use one-dimensional cellular space to simulate the operation of the urban rainwater pipe network. Each cell adopts a uniform slope and cross-sectional scale. The runoff and non-point source pollution input of the entire pipe network only come from the cells on the surface connected to the pipe network entrance. In a smaller time step, the rainwater in the urban rainwater pipe network is regarded as static. Therefore, the Manning formula is used to calculate the runoff and non-point source pollution transmission process in the urban rainwater pipe network.

[0012] Step (7): When rainfall occurs in the target river section, the non-point source pollution load generated by it is simulated and calculated through steps (3) to (6). When the core pollutant concentration reaches the critical urban rainfall runoff core pollutant load index for issuing a warning of river black and odor phenomenon, Immediately issue a warning for black and smelly rivers.

[0013] Furthermore, the specific process of obtaining the core pollutants in rainfall runoff through principal component analysis in step (2) is as follows:

[0014] The concentration of each pollutant x ij Standardization is to subtract the mean of the same variable and then divide it by the standard deviation to eliminate the dimension effect;

[0015]

[0016] In the formula, is the jth pollutant in the i-th rainfall after standardization; is the sample mean of the j-th pollutant; s j is the standard deviation of the jth pollutant;

[0017] In the standardized data matrix X = (x ij ) is used to calculate the original index correlation coefficient matrix R = (r ij ),in:

[0018]

[0019] In the formula, r ij is the correlation coefficient between the i-th pollutant and the j-th pollutant;

[0020] Find the p eigenvalues ​​λ of the R matrix 1 ≥λ 2 ≥…≥λ p and the corresponding regularized unit eigenvector c j =(c 1j , c 2j , …c pj )′, where each eigenvalue is the variance of the corresponding principal component. The larger the variance, the greater the contribution to the total variation.

[0021]

[0022] Where y j is the jth principal component; is the kth standardized indicator variable;

[0023] The principal components are reasonably selected by calculating the information contribution rate and cumulative contribution rate of m eigenvalues. The calculation formula is as follows:

[0024]

[0025] Where, d j is the jth principal component y j Information contribution rate; a j is the jth principal component yj The cumulative contribution rate of the main components is determined by setting the threshold, which is the core pollutant in the rainfall runoff.

[0026] Furthermore, in step (4), the runoff depth h of each cell is calculated according to the mass conservation principle through the rainfall R, vegetation interception rainfall P, infiltration volume I and storage volume DS, and the calculation formula is as follows:

[0027] h=RPI-DS

[0028] Where, h is the runoff depth of the cell, mm; R is the total rainfall, mm; P is the rainfall intercepted by vegetation, mm; I is the infiltration, mm; DS is the storage, mm;

[0029] The infiltration rate I is calculated by the Horton model, and the calculation formula is as follows:

[0030]

[0031] Where, I is the infiltration rate, mm; f u is the steady state or minimum infiltration rate, mm / s; f 0 is the initial or maximum infiltration rate, mm / s; k d is the infiltration capacity attenuation coefficient, s -1 ; t is the duration of rainfall, s -1 ; ts is the time step; e is the natural constant;

[0032] Vegetation interception rainfall P refers to the ability of the surface covered by vegetation to intercept rainwater during rainfall. The calculation formula is as follows:

[0033]

[0034] P max =0.935+0.498LAI-0.00575LAI 2

[0035] Where, P is the rainfall intercepted by vegetation, mm; R cum is the cumulative rainfall, mm; LAI is the leaf area index; P max is the maximum storage rainfall, which is a function of LAI.

[0036] Furthermore, in step (4), the water volume Q of cells in each direction is distributed i The calculation is as follows: calculate the average water depth of the central cell and its domain cells, exclude the cells with water depth exceeding the average in the domain cells, and do not allocate water. Continue to execute this process until no domain cells need to be excluded. At this time, the water volume of the central cell is allocated to the remaining domain cells according to the principle that the water depth of the remaining domain cells after allocation is the same. The calculation formula is as follows:

[0037]

[0038] In the formula, Q i is the amount of water transferred from the uncorrected central cell to the neighboring cell i; h i is the runoff depth of the ith neighborhood cell, mm; m is the number of remaining neighborhood cells.

[0039] Furthermore, the flow correction in step (4) is specifically as follows: based on the determination of flow generation and flow direction, for the case where some cells cannot complete the complete water distribution within one time step, the Manning formula is used to correct the minimum difference method in time. The calculation formula is as follows:

[0040]

[0041] Where T is the time required for the water depth of the central cell to transfer to the neighboring cells, that is, the water volume / pollutant transfer time step; V is the flow velocity, m / s; h is the runoff depth, m; j is the water surface slope between the central cell and the i-th neighboring cell; n is the Manning roughness coefficient; L is the distance between cells in the direction that needs time correction; t is the model time step; Q ci represents the amount of water transferred from the central cell to the neighboring cell i after correction;

[0042] After calculating the amount of water transferred by each neighborhood cell Q ci The total amount of water transferred can be obtained by summing it up, and then compared with the water volume of the central cell. If the water volume of the central cell is less than the total amount of water transferred, that is, the central cell does not have enough water to transfer, the amount of water transferred in each neighboring cell needs to be reduced according to the water depth, and Q is recalculated. ci If the water depth of the central cell is greater than the total amount of water transferred, the amount of water transferred remains unchanged. This rule is applied to the entire cellular space. The amount of water transferred and the remaining amount of water in all cells in the entire cellular space at each moment are calculated. Based on the rainfall and infiltration at the next moment, the cellular water volume at the end of the next moment is obtained. The calculation is repeated until the entire simulation process ends.

[0043] Furthermore, in step (5), the non-point source pollution washoff load is calculated by using an exponential function washoff model formula to calculate the pollution load generated by the non-point source pollution washoff of each cell, and the calculation formula is as follows:

[0044]

[0045] Where w is the pollution load caused by flushing, mg; K W is the scour coefficient; N W is the scour index; m B is the accumulated amount of residual pollutants in each cell at each time, mg;

[0046] Calculation of the accumulated amount of surface pollutants in step (5): The accumulated amount of residual pollutants in each cell at each time is calculated according to the saturated function accumulation model and comprehensive consideration of cleaning management measures and runoff erosion. The calculation formula is as follows:

[0047] m B =B max ad / (k b +ad)×A×(1-SSE)-w t-1

[0048] Where: B max is the maximum possible accumulation of pollutants per unit area on the surface, mg / mm 2 ;k b is the half-saturation accumulation constant, that is, the number of days required to reach half of the maximum pollution load accumulation, d; ad is the number of dry days before rainfall, d; SSE is the removal rate of accumulated pollutants by cleaning measures; w t-1 is the cumulative pollutant load removed by runoff at the previous moment, mg; A is the area of ​​a single cell, m 2 .

[0049] Furthermore, in step (5), the non-point source pollution load and concentration of the cells are calculated as follows: pollutants are transferred and exchanged between the neighboring cells along the runoff direction, thereby obtaining the net input of the non-point source pollution load of each cell. After comprehensively considering the non-point source pollution loss caused by infiltration, the non-point source pollution load and concentration of each cell in a single time step can be updated. The calculation formula is as follows:

[0050] l=Q ci ×ts×A×10 -6 ×C+w

[0051] L(i,j)=l(i+1,j+1)+l(i+1,j)+l(i+1,j-1)+l(i,j+1)+l(i,j-1)+l(i-1,j+1)+l(i-1,j)+l(i-1,j-1)+∑l(i,j)

[0052] Where: l represents the non-point source pollution load transmitted by each cell to the neighboring cells along the runoff direction in each time step, mg; C represents the non-point source pollution concentration in each cell at the current moment, mg / L; L(i,j) represents the net input of non-point source pollution load in the cell located at coordinate (i, j), mg; l(i+1,j+1)+l(i+1,j)+l(i+1,j-1)+l(i,j+1)+l(i,j-1)+l(i-1,j+1)+l(i-1,j-1)+l(i-1,j+1)+l(i-1,j)+l(i-1,j-1) are the non-point source pollution loads input from each neighboring cell, mg; ∑l(i,j) represents the sum of non-point source pollution loads output from the (i,j) cell to neighboring cells in all directions, mg;

[0053] The non-point source pollution load of each cell at the end of the current moment is obtained by calculation, and the calculation is repeated until the entire simulation process is completed.

[0054] Furthermore, in step (5), the non-point source pollution load and concentration of each cell in a single time step can be updated by comprehensively considering the non-point source pollution loss caused by infiltration:

[0055] m t+1 =Q r C r +L(i,j)-Q i C

[0056]

[0057] Q i =(I 0 +ft c )×A / 10 6

[0058] In the formula, m t+1 represents the updated surface non-point source pollutant load in each cell, mg; C represents the non-point source pollution concentration in each cell at the current moment, mg / L; Q r Represents the rainfall input by each cell, L; C r is the pollutant concentration in rainfall, mg / L; Q i Represents the infiltration runoff, L.

[0059] Furthermore, the calculation of the runoff transmission process in the urban rainwater pipe network in step (6) is as follows: In a smaller time step, the rainwater in the urban rainwater pipe network can be regarded as static, so the Manning formula is used to calculate the runoff transmission process in the urban rainwater pipe network. The calculation formula is as follows:

[0060]

[0061] Where: q prepresents the runoff output from the central cell to the downstream cell, mm3 / s; H p represents the runoff depth of the central cell, mm; s p Represents the pipeline slope; n p represents the pipe Manning coefficient; d p represents the cross-sectional size, mm;

[0062] Calculation of the transmission process of non-point source pollution in urban rainwater pipe networks: In a smaller time step, the rainwater in the urban rainwater pipe network can be regarded as static, so the Manning formula is used to calculate the transmission process of non-point source pollution in the urban rainwater pipe network. The calculation formula is as follows:

[0063] l p =q p ×ts×10 -6 ×Cp

[0064] l p Represents the non-point source pollution load output from the central cell to the downstream, mg; Cp represents the non-point source pollution concentration in each pipe network cell, mg / L.

[0065] Furthermore, in step (6), the global simulation of the cell state in the urban rainwater pipe network is as follows: the runoff and non-point source pollution load in the pipe cell in each time step are only determined by the cell states of the two neighboring cells and the previous time step itself. The formula for calculating the runoff and non-point source pollution load of the pipe cell at each time is as follows:

[0066]

[0067]

[0068] Where: Q p_t+1 and Q p_t Represents the runoff in the pipeline cell at the current moment and the next moment, mm 3 ;P p_t and P p_t+1 Respectively represent the non-point source pollution load in the pipeline cell at the current moment and the next moment, mg; k is the first-order attenuation coefficient, d-1; and are the inflow and outflow of each cell, mm 3 ; and Respectively represent the non-point source pollution load input and output in each cell, mg;

[0069] The non-point source pollution load of each cell in the entire cellular space at the end of the current moment is obtained, and the calculation is repeated until the entire simulation process is completed. The beneficial effects of the present invention are:

[0070] Compared with the urban non-point source pollution model based on sub-catchment areas, the cellular automaton has a grid structure that matches the resolution of the input raster data and can fully represent the urban surface characteristics. Therefore, the cellular automaton algorithm has a better ability to simulate urban surface rainfall runoff processes.

[0071] Compared with the prior art, the present invention takes into account the internal convergence process of the surface sub-catchment area of ​​urban rainfall runoff when calculating the non-point source pollution load generated by rainfall. The model takes into account the impact of the internal convergence process of the surface sub-catchment area on urban rainfall runoff, uses a real time step, and compared with the traditional model, the model calculation unit proposed in the present invention is not a sub-catchment area with only a single geographical feature. It can not only accurately simulate the urban surface rainfall runoff process, but also simulate the runoff pollution distribution law under different rainfall intensities and the rainfall runoff pollution load in the study area, thereby improving the accuracy of early warning. BRIEF DESCRIPTION OF THE DRAWINGS

[0072] Figure 1 It is a schematic diagram of the process of the present invention,

[0073] Figure 2 It is a flow chart of the water allocation algorithm of the present invention. DETAILED DESCRIPTION

[0074] The present invention is further explained below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the following specific embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention.

[0075] Combined with Figure 1 It can be seen that the method for early warning of river blackness and odor based on urban rainfall runoff pollution load simulation disclosed in the embodiment of the present invention includes the following steps:

[0076] (1) Select the river section in the urban small watershed that needs to be warned of river black and odor as the target river section, and collect the rainfall runoff data generated by the n rainfall events corresponding to the black and odorous water bodies in the target river section, where n is an integer ≥ 5; determine the location of the rainwater outlet in the target river section according to the pipe network data and field survey, and collect the rainfall runoff data of the n rainfall events corresponding to the black and odorous events at the rainwater outlet;

[0077] The rainfall events corresponding to the black and smelly events refer to the rainfall events that caused the black and smelly events in the river, and the rainfall runoff data include the concentration and total flow of each pollutant in the rainfall runoff.

[0078] This step specifically includes:

[0079] (1-1) Select a small urban watershed river section that needs to be warned of black and odorous water as the target river section, and collect rainfall runoff data generated by n rainfall events corresponding to black and odorous water bodies in the target river section, where n is an integer ≥5.

[0080] (1-2) Collect rainfall runoff data corresponding to the n black and odor events at the rainwater outlet. Use polyethylene bottles as sampling containers and adopt the "dense first, sparse later" sampling method, that is, collect 500 ml of water samples every 5 minutes in the first 30 minutes of runoff formation at each point, and then collect 500 ml of water samples every 15 minutes until the end of rainfall runoff. When sampling, ensure that the water sample fills the container and no air is left in the bottle. If the runoff volume at a certain point in time is too small, the sampling time can be appropriately extended until a considerable volume of water samples is collected.

[0081] (2) Perform principal component analysis on the rainfall runoff data generated by the n rainfalls corresponding to the black and odorous water bodies in step (1) to obtain the core pollutants in the rainfall runoff. Calculate the average pollution load of the rainfall runoff data generated by the n rainfalls corresponding to the black and odorous water bodies of the screened core pollutants, and record it as It is the critical urban rainfall runoff core pollutant load index for issuing warnings on black and smelly river phenomena.

[0082] This step specifically includes:

[0083] (2-1) The specific steps of mathematical principles and formula derivation are as follows:

[0084] The concentration of each pollutant x ij Standardization is to subtract the mean of the same variable and then divide it by the standard deviation to eliminate the dimension effect;

[0085]

[0086] In the formula, is the jth pollutant in the i-th rainfall after standardization; is the sample mean of the j-th pollutant; s j is the standard deviation of the jth pollutant;

[0087] In the standardized data matrix X = (x ij ) is used to calculate the original index correlation coefficient matrix R = (r ij ),in:

[0088]

[0089] In the formula, r ij is the correlation coefficient between the i-th pollutant and the j-th pollutant;

[0090] Find the p eigenvalues ​​λ of the R matrix 1 ≥λ 2 ≥…≥λ p and the corresponding regularized unit eigenvector c j =(c 1j , c 2j, …c pj )′, where each eigenvalue is the variance of the corresponding principal component. The larger the variance, the greater the contribution to the total variation.

[0091]

[0092] Where y j is the jth principal component; is the kth standardized indicator variable;

[0093] The principal components are reasonably selected by calculating the information contribution rate and cumulative contribution rate of m eigenvalues. The calculation formula is as follows:

[0094]

[0095] Where, d j is the jth principal component y j Information contribution rate; a j is the jth principal component y j The cumulative contribution rate of the main component is determined by setting a threshold, generally taking 85%, which is the core pollutant in rainfall runoff.

[0096] (3) Obtain the land use type, digital elevation data (DEM) and rainfall changing over time in the study area, and set up a cellular space that matches the raster data, including cell size, cell shape and boundary cells, set the model running time step, and establish the basic geographical scene of the model.

[0097] This step specifically includes:

[0098] (3-1) Obtain the land use type and digital elevation data (DEM) of the study area to construct the basic geographic scene of the model, and set the cellular space matching the raster data accordingly, and define the size, land use type, and Manning roughness coefficient of each cell. In the present invention, the Moore-type eight-neighborhood is used to define the neighborhood relationship, and the boundary cells are set to the maximum value to ensure that water cannot enter.

[0099] (3-2) The rainfall data of the study area is measured by a rain gauge or obtained through a meteorological station. The rainfall data is spatially interpolated using ArcGIS software to obtain a raster surface of the rainfall data, that is, the rainfall data of each cell at different times.

[0100] (4) According to the set underlying surface infiltration parameters (initial loss, average infiltration rate after loss, etc.), the flow generation and flow direction are calculated, and then the current water depth of each cell is obtained through confluence calculation.

[0101] This step specifically includes:

[0102] (4-1) Runoff calculation: According to the principle of mass conservation, the runoff depth of each cell is calculated by rainfall, vegetation interception rainfall, infiltration and storage. By setting rainfall and storage, vegetation interception rainfall and infiltration are calculated, and the runoff depth of each cell is further calculated. The formula is as follows:

[0103] h=RPI-DS

[0104] Where h is the runoff depth of the cell, mm; R is the total rainfall, mm; P is the rainfall intercepted by vegetation, mm; I is the rainfall lost by infiltration, mm; DS is the storage capacity, mm.

[0105] The infiltration rate is calculated by Horton model, and the calculation formula is as follows:

[0106]

[0107] Where, I is the rainfall loss due to infiltration, mm; f u is the steady state or minimum infiltration rate, mm / s; f 0 is the initial or maximum infiltration rate, mm / s; k d is the infiltration capacity attenuation coefficient, s -1 ; t is the duration of rainfall, s -1 ; ts is the time step.

[0108] Vegetation interception rainfall refers to the ability of the surface covered by vegetation to intercept rainwater during rainfall. The calculation formula is as follows:

[0109]

[0110] P max =0.935+0.498LAI-0.00575LAI 2

[0111] Where, P is the rainfall intercepted by vegetation, mm; R cum is the cumulative rainfall, mm; LAI is the leaf area index; P max is the maximum storage rainfall, which is a function of LAI.

[0112] According to the model time step, the rainfall and storage of each cell are calculated and compared. When the rainfall exceeds the storage, the surface begins to produce runoff. Applying this rule to the entire cellular space, the runoff depth of all cells at each time step can be obtained.

[0113] (4-2) Calculate the amount of water to be distributed to cells in each direction: Calculate the average value of the water depth of the central cell and its domain cells, exclude the cells in the domain cells whose water depth exceeds the average value, and do not distribute water to them. Continue this process until no domain cells need to be excluded. At this time, the water volume of the central cell is distributed to the domain cells according to the principle that the water depth of the remaining domain cells after distribution is the same. The algorithm flow chart is shown in the figure below: Figure 2 As shown, the calculation formula is as follows:

[0114]

[0115] (4-3) Flow correction calculation: When using the minimum difference method, if some cells cannot complete the complete water distribution within one time step, the Manning formula is used to make a time correction to the minimum difference method.

[0116] Specifically, assume that the water of the central cell flows into k neighboring cells, and the i-th cell represents one of the k neighboring cells. First, the time T required for the water depth h of the central cell to transfer to the i-th neighboring cell is calculated according to the Manning formula (that is, the water volume / pollutant transfer time step), and the calculation formula is as follows:

[0117]

[0118] Among them, T is the time required for the water depth of the central cell to be transferred to the neighboring cells, that is, the time step of water volume / pollutant transfer; V is the flow velocity, m / s; h is the water depth of the central cell, m; j is the water surface slope between the central cell and the i-th neighboring cell; n is the Manning roughness coefficient; L is the distance between cells in the direction that requires time correction.

[0119] After the flow time is obtained, the allocated water volume of each domain cell is corrected in combination with the specified time step. If the total allocated water volume exceeds the total water volume of the central cell, further correction is performed. The calculation formula is as follows:

[0120]

[0121] Q ci It represents the amount of water transferred from the central cell to the neighboring cell i, ts is the model time step, and D is the cell side length.

[0122] After calculating the amount of water transferred by each neighborhood cell Q ci The total amount of water transferred can be obtained by summing it up, and then compared with the water volume of the central cell. If the water volume of the central cell is less than the total amount of water transferred, that is, the central cell does not have enough water to transfer, the amount of water transferred in each neighboring cell needs to be reduced according to the water depth, and Q is recalculated. ci; If the water depth of the central cell is greater than the total amount of water transferred, the amount of water transferred remains unchanged. Apply this rule to the entire cellular space, and calculate the amount of water transferred and the amount of water remaining in all cells in the entire cellular space at each moment.

[0123] Through the above calculation, the water volume of each cell at the end of the current moment can be obtained. The water volume of each cell at the end of the current moment is used as the water volume of the cell at the beginning of the next moment. According to the rainfall and infiltration amount of the next moment step, the water volume of the cell at the end of the next moment is obtained. The calculation is repeated until the whole simulation process is completed.

[0124] (5) An exponential function washoff model is used to calculate the non-point source pollution washoff load in each cell, and a saturated function accumulation model is used to calculate and simulate the accumulation of surface pollutants during the initial dry period. Cleaning management measures and runoff washoff are taken into consideration. Pollutants generated by washoff are transferred and exchanged between neighboring cells along the runoff transmission direction. The net input of non-point source pollution load in each cell is calculated. After comprehensively considering the non-point source pollution loss caused by infiltration, the non-point source pollution load and concentration update of each cell within a single time step can be achieved.

[0125] This step specifically includes:

[0126] (5-1) Calculation of non-point source pollution washoff load: The pollution load generated by non-point source pollution washoff of each cell is calculated using the exponential function washoff model formula, which is widely used. The calculation formula is as follows:

[0127]

[0128] Where w is the pollution load caused by flushing, mg; K W is the scour coefficient; N W is the scour index; m B is the residual pollutant accumulation in each cell at each time, mg. K of different land use types W and N W It is an empirical coefficient, and its initial value can be obtained through relevant literature and further calibrated according to measured data.

[0129] (5-2) Calculation of surface pollutant accumulation: The residual pollutant accumulation in each cell at each time is calculated according to the saturation function accumulation model and comprehensive consideration of cleaning management measures and runoff erosion. The calculation formula is as follows:

[0130] m B =B max ad / (k b +ad)×A×(1-SSE)-w t-1

[0131] Where: B max is the maximum possible accumulation of pollutants per unit area on the surface, mg / mm2 ;k b is the half-saturation accumulation constant, that is, the number of days required to reach half of the maximum pollution load accumulation, d; ad is the number of dry days before rainfall, d; SSE is the removal rate of accumulated pollutants by cleaning measures; w t-1 is the cumulative pollutant load removed by runoff at the previous moment, mg.

[0132] (5-3) Calculation of non-point source pollution load and concentration of cells: Pollutants are transferred and exchanged between neighboring cells along the runoff direction, thereby obtaining the net input of non-point source pollution load of each cell. After comprehensively considering the non-point source pollution loss caused by infiltration, the non-point source pollution load and concentration of each cell can be updated within a single time step. The calculation formula is as follows:

[0133] l=Q ci ×ts×A×10 -6 ×C+w

[0134] L(i,j)=l(i+1,j+1)+l(i+1,j)+l(i+1,j-1)+l(i,j+1)+l(i,j-1)+l(i-1,j+1)+l(i-1,j)+l(i-1,j-1)+∑l(i,j)

[0135] m t+1 =Q r C r +L(i,j)-Q i C

[0136]

[0137] Q i =(I 0 +ft c )×A / 10 6

[0138] In the formula: l represents the non-point source pollution load transmitted by each cell to the neighboring cells along the runoff direction in each time step, mg; C represents the non-point source pollution concentration in each cell at the current moment, mg / L. L(i,j) represents the net input of non-point source pollution load in the cell located at coordinate (i, j), mg; l(i+1,j+1)+l(i+1,j)+l(i+1,j-1)+l(i,j+1)+l(i,j-1)+l(i-1,j+1)+l(i-1,j+1)+l(i-1,j)+l(i-1,j-1) are the non-point source pollution loads input from each neighboring cell, mg; ∑l(i,j) represents the sum of non-point source pollution loads output from the (i, j) cell to neighboring cells in all directions, mg. m t+1represents the updated surface non-point source pollutant load in each cell, mg; C represents the non-point source pollution concentration in each cell at the current moment, mg / L; Q r Represents the rainfall input by each cell, L; C r is the pollutant concentration in rainfall, mg / L; Q i Represents the infiltration runoff, L.

[0139] The non-point source pollution load of each cell at the end of the current moment is obtained by calculation, and the calculation is repeated until the entire simulation process is completed.

[0140] (6) A one-dimensional cellular space is used to simulate the operation of the urban rainwater pipe network. Each cell adopts a uniform slope and cross-sectional scale. The runoff and non-point source pollution input of the entire pipe network only come from the cells on the surface connected to the pipe network entrance. The runoff in the urban rainwater pipe network can be regarded as static within a smaller time step. Therefore, the Manning formula is used to calculate the transmission process of runoff and non-point source pollution in the urban rainwater pipe network.

[0141] This step specifically includes:

[0142] (6-1) Calculation of runoff transmission process in urban rainwater pipe network: In a smaller time step, the rainwater in the urban rainwater pipe network can be regarded as static, so the Manning formula is used to calculate the runoff transmission process in the urban rainwater pipe network. The calculation formula is as follows:

[0143]

[0144] Where: q p Represents the runoff output from the central cell to the downstream cell, mm 3 / s;H p represents the runoff depth of the central cell, mm; s p Represents the pipeline slope; n p represents the pipe Manning coefficient; d p Represents the cross-sectional size, mm.

[0145] (6-2) Calculation of the transmission process of non-point source pollution in urban rainwater pipe networks: In a smaller time step, the rainwater in the urban rainwater pipe network can be regarded as static, so the Manning formula is used to calculate the transmission process of non-point source pollution in the urban rainwater pipe network. The calculation formula is as follows:

[0146] l p =q p ×ts×10 -6 ×Cp

[0147] l p Represents the non-point source pollution load output from the central cell to the downstream, mg; Cp represents the non-point source pollution concentration in each pipe network cell, mg / L.

[0148] (6-3) Global simulation of cellular states in urban stormwater pipe networks:

[0149] The runoff and non-point source pollution load in the pipeline cell in each time step are only determined by the cell states of the two neighboring cells and the previous time step. The formula for calculating the runoff and non-point source pollution load of the pipeline cell at each time is as follows:

[0150]

[0151]

[0152] Where: Q p_t+1 and Q p_t Represents the runoff in the pipeline cell at the current moment and the next moment, mm 3 ;P p_t and P p_t+1 represents the non-point source pollution load in the pipeline cell at the current moment and the next moment, mg; k is the first-order attenuation coefficient, d -1 ; and are the inflow and outflow of each cell, mm 3 ; and Represent the input and output of non-point source pollution load in each cell, mg respectively.

[0153] With the above-mentioned ideal embodiments of the present invention as inspiration, through the above-mentioned description content, relevant personnel can make various changes and modifications without departing from the scope of the technical idea of ​​the present invention.

Claims

1. A method for early warning of river blackness and odor based on simulation of urban rainfall runoff pollution load, characterized in that: The steps include: Step (1): Select a small urban watershed river section that needs to be warned of river black and odor as the target river section, collect rainfall runoff data generated by n rainfall events corresponding to black and odorous water bodies in the target river section, where n is an integer ≥ 5, and the rainfall runoff data includes the concentration and total flow of each pollutant in the rainfall runoff; determine the location of the rainwater outlet in the watershed of the target river section based on the pipe network data and field survey, and collect rainfall runoff data of the rainfall events corresponding to the n black and odorous events at the rainwater outlet; Step (2): Perform principal component analysis on the rainfall runoff data generated by the n rainfalls corresponding to the black and odorous water bodies in step (1) to obtain the core pollutants in the rainfall runoff, and calculate the average pollution load of the rainfall runoff data generated by the n rainfalls corresponding to the black and odorous water bodies of the screened core pollutants, which is recorded as That is, the critical urban rainfall runoff core pollutant load index for issuing warnings of black and smelly river phenomena; Step (3): determine the water collection range of the rainwater outlet as the study area of ​​urban rainfall runoff pollution, obtain the land use type, digital elevation data (DEM) and rainfall changing over time of the study area, and set a cellular space matching the raster data accordingly. The cellular space includes cell size, cell shape and boundary cells, set the running time step of the urban rainfall runoff pollution load accounting model based on cellular automata, and establish the basic geographical scene of the urban rainfall runoff pollution load accounting model based on cellular automata; the cellular space is the geographical space of the study area, that is, the water collection range of the rainwater outlet, which is composed of cells; the cell shape is a square grid, and after the study area is rasterized, each grid corresponds to a cell; the rainfall data of the study area is obtained by measuring with a rain gauge or through a meteorological station, and the rainfall data is spatially interpolated using ArcGIS software to obtain the raster surface of the rainfall data, that is, the rainfall data of each cell at different times is obtained; Step (4): According to the principle of conservation of mass, the net rain depth of each cell is calculated through rainfall, vegetation interception rainfall, infiltration and depression storage. The water flows in multiple directions downstream. The water level status of the central cell and the neighboring cells is considered as a whole. The minimum difference method commonly used in the multi-flow method is used to preliminarily calculate the water distribution, so that the system reaches a state of water level balance after water distribution. On the basis of the flow calculated by the minimum difference method, the Manning formula is used to correct the flow; Step (5): Use the exponential function washoff model to calculate the non-point source pollution washoff load in each cell, use the saturated function accumulation model to calculate and simulate the initial dry period surface pollutant accumulation, and comprehensively consider the cleaning management measures and runoff washoff. The pollutants generated by the washoff are transmitted and exchanged between each neighboring cell along the runoff transmission direction. The net input of the non-point source pollution load of each cell is calculated. After comprehensively considering the non-point source pollution loss caused by infiltration, the non-point source pollution load and concentration of each cell can be updated within a single time step; Step (6): Use one-dimensional cellular space to simulate the operation of the urban rainwater pipe network. Each cell adopts a uniform slope and cross-sectional scale. The runoff and non-point source pollution input of the entire pipe network only come from the cells on the surface connected to the pipe network entrance. In a smaller time step, the rainwater in the urban rainwater pipe network is regarded as static. Therefore, the Manning formula is used to calculate the runoff and non-point source pollution transmission process in the urban rainwater pipe network. Step (7): When rainfall occurs in the target river section, the non-point source pollution load generated by it is simulated and calculated through steps (3) to (6). When the core pollutant concentration reaches the critical urban rainfall runoff core pollutant load index for issuing a warning of river black and odor phenomenon, Immediately issue a warning for black and smelly rivers.

2. The method for early warning of river blackness and odor based on simulation of urban rainfall runoff pollution load according to claim 1 is characterized in that: The specific process of obtaining the core pollutants in rainfall runoff through principal component analysis in step (2) is as follows: The concentration of each pollutant x ij Standardization is to subtract the mean of the same variable and then divide it by the standard deviation to eliminate the dimension effect; In the formula, is the jth pollutant in the i-th rainfall after standardization; is the sample mean of the j-th pollutant; s j is the standard deviation of the jth pollutant; In the standardized data matrix X = (x ij ) is used to calculate the original index correlation coefficient matrix R = (r ij ),in: In the formula, r ij is the correlation coefficient between the i-th pollutant and the j-th pollutant; Find the p eigenvalues ​​of the matrix R λ1≥λ2≥…≥λ p and the corresponding regularized unit eigenvector c j =(c 1j , c 2j , …c pj )′, where each eigenvalue is the variance of the corresponding principal component. The larger the variance, the greater the contribution to the total variation. Where y j is the jth principal component; is the kth standardized indicator variable; The principal components are reasonably selected by calculating the information contribution rate and cumulative contribution rate of m eigenvalues. The calculation formula is as follows: Where, d j is the jth principal component y j Information contribution rate; a j is the jth principal component y j The cumulative contribution rate of the main components is determined by setting the threshold, which is the core pollutant in the rainfall runoff.

3. The method for early warning of river blackness and odor based on simulation of urban rainfall runoff pollution load according to claim 1 is characterized in that: In step (4), the runoff depth h of each cell is calculated according to the principle of mass conservation through the rainfall R, vegetation interception rainfall P, infiltration volume I and storage volume DS. The calculation formula is as follows: h=RPI-DS Where, h is the runoff depth of the cell, mm; R is the total rainfall, mm; P is the rainfall intercepted by vegetation, mm; I is the infiltration, mm; DS is the storage, mm; The infiltration rate I is calculated by the Horton model, and the calculation formula is as follows: Where, I is the infiltration rate, mm; f u is the steady state or minimum infiltration rate, mm / s; f0 is the initial or maximum infiltration rate, mm / s; k d is the infiltration capacity attenuation coefficient, s -1 ; t is the duration of rainfall, s -1 ; ts is the time step; e is the natural constant; Vegetation interception rainfall P refers to the ability of the surface covered by vegetation to intercept rainwater during rainfall. The calculation formula is as follows: P max =0.935+0.498LAI-0.00575LAI 2 Where, P is the rainfall intercepted by vegetation, mm; R cum is the cumulative rainfall, mm; LAI is the leaf area index; P max is the maximum storage rainfall, which is a function of LAI.

4. The method for early warning of river blackness and odor based on simulation of urban rainfall runoff pollution load according to claim 1 is characterized in that: In step (4), the amount of water Q distributed to cells in each direction is i The calculation is as follows: calculate the average water depth of the central cell and its domain cells, exclude the cells with water depth exceeding the average in the domain cells, and do not allocate water. Continue to execute this process until no domain cells need to be excluded. At this time, the water volume of the central cell is allocated to the remaining domain cells according to the principle that the water depth of the remaining domain cells after allocation is the same. The calculation formula is as follows: In the formula, Q i is the amount of water transferred from the uncorrected central cell to the neighboring cell i; h is the runoff depth of the i-th neighboring cell, mm; m is the number of remaining neighboring cells.

5. The method for early warning of river blackness and odor based on simulation of urban rainfall runoff pollution load according to claim 1 is characterized in that: The flow correction in step (4) is specifically as follows: based on the determination of flow generation and flow direction, for the case where some cells cannot complete the complete water distribution within one time step, the minimum difference method is corrected in time using the Manning formula, and the calculation formula is as follows: Where T is the time required for the water depth of the central cell to transfer to the neighboring cells, that is, the water volume / pollutant transfer time step; V is the flow velocity, m / s; h is the runoff depth, m; j is the water surface slope between the central cell and the i-th neighboring cell; n is the Manning roughness coefficient; L is the distance between cells in the direction that needs time correction; t is the model time step; Q ci represents the amount of water transferred from the central cell to the neighboring cell i after correction; After calculating the amount of water transferred by each neighborhood cell Q ci The total amount of water transferred can be obtained by summing it up, and then compared with the water volume of the central cell. If the water volume of the central cell is less than the total amount of water transferred, that is, the central cell does not have enough water to transfer, the amount of water transferred in each neighboring cell needs to be reduced according to the water depth, and Q is recalculated. ci If the water depth of the central cell is greater than the total amount of water transferred, the amount of water transferred remains unchanged. This rule is applied to the entire cellular space. The amount of water transferred and the remaining amount of water in all cells in the entire cellular space at each moment are calculated. Based on the rainfall and infiltration at the next moment, the cellular water volume at the end of the next moment is obtained. The calculation is repeated until the entire simulation process ends.

6. The method for early warning of river blackness and odor based on simulation of urban rainfall runoff pollution load according to claim 1 is characterized in that: In the step (5), the non-point source pollution washoff load is calculated by using an exponential function washoff model formula to calculate the pollution load generated by the non-point source pollution washoff of each cell. The calculation formula is as follows: Where w is the pollution load caused by flushing, mg; K W is the scour coefficient; N W is the scour index; m B is the accumulated amount of residual pollutants in each cell at each time, mg; Calculation of the accumulated amount of surface pollutants in step (5): The accumulated amount of residual pollutants in each cell at each time is calculated according to the saturated function accumulation model and comprehensive consideration of cleaning management measures and runoff erosion. The calculation formula is as follows: m B =B max ad / (k b +ad)×A×(1-SSE)-w t-1 Where: B max is the maximum possible accumulation of pollutants per unit area on the surface, mg / mm 2 ;k b is the half-saturation accumulation constant, that is, the number of days required to reach half of the maximum pollution load accumulation, d; ad is the number of dry days before rainfall, d; SSE is the removal rate of accumulated pollutants by cleaning measures; w t-1 is the cumulative pollutant load removed by runoff at the previous moment, mg; A is the area of ​​a single cell, m 2 .

7. The method for early warning of river blackness and odor based on simulation of urban rainfall runoff pollution load according to claim 1 is characterized in that: The calculation of the non-point source pollution load and concentration of the cells in step (5) is as follows: pollutants are transferred and exchanged between the neighboring cells along the runoff direction, thereby obtaining the net input of the non-point source pollution load of each cell. After comprehensively considering the non-point source pollution loss caused by infiltration, the non-point source pollution load and concentration of each cell in a single time step can be updated. The calculation formula is as follows: l=Q ci ×ts×A×10 -6 ×C+w L(i,j)=l(i+1,j+1)+l(i+1,j)+l(i+1,j-1)+l(i,j+1)+l(i,j-1)+l(i-1,j+1)+l(i-1,j)+l(i-1,j-1)+∑l(i,j) Where: l represents the non-point source pollution load transmitted by each cell to the neighboring cells along the runoff direction in each time step, mg; C represents the non-point source pollution concentration in each cell at the current moment, mg / L; L(i, j) represents the net input of non-point source pollution load in the cell at coordinate (i, j), mg; l(i+1, j+1)+l(i+1, j)+l(i+1, j-1)+l(i, j+1)+l(i, j-1)+l(i-1, j+1)+l(i-1, j)+l(i-1, j-1) are the non-point source pollution loads input from each neighborhood cell, mg; ∑l(i, j) represents the sum of the non-point source pollution loads output from the (i, j) cell to the neighboring cells in all directions, mg; The non-point source pollution load of each cell at the end of the current moment is obtained by calculation, and the calculation is repeated until the entire simulation process is completed.

8. The method for early warning of river blackness and odor based on simulation of urban rainfall runoff pollution load according to claim 1 is characterized in that: In step (5), the non-point source pollution load and concentration of each cell in a single time step can be updated by comprehensively considering the non-point source pollution loss caused by infiltration: m t+1 =QrCr+L(i,j)-Q i C Q i =(I0+ft c )×A / 10 6 In the formula, m t+1 represents the updated surface non-point source pollutant load in each cell, mg; C represents the non-point source pollution concentration in each cell at the current moment, mg / L; Q r Represents the rainfall input by each cell, L; C r is the pollutant concentration in rainfall, mg / L; Q i Represents the infiltration runoff, L.

9. The method for early warning of river blackness and odor based on simulation of urban rainfall runoff pollution load according to claim 1 is characterized in that: The calculation of the runoff transmission process in the urban rainwater pipe network in step (6): the rainwater in the urban rainwater pipe network can be regarded as static in a smaller time step, so the Manning formula is used to calculate the runoff transmission process in the urban rainwater pipe network. The calculation formula is as follows: Where: q p represents the runoff output from the central cell to the downstream cell, mm3 / s; H p represents the runoff depth of the central cell, mm; s p Represents the pipeline slope; n p represents the pipe Manning coefficient; d p represents the cross-sectional size, mm; Calculation of the transmission process of non-point source pollution in urban rainwater pipe networks: In a smaller time step, the rainwater in the urban rainwater pipe network can be regarded as static, so the Manning formula is used to calculate the transmission process of non-point source pollution in the urban rainwater pipe network. The calculation formula is as follows: l p =q p ×ts×10 -6 ×Cp l p Represents the non-point source pollution load output from the central cell to the downstream, mg; Cp represents the non-point source pollution concentration in each pipe network cell, mg / L.

10. The method for early warning of river blackness and odor based on simulation of urban rainfall runoff pollution load according to claim 1 is characterized in that: The step (6) is a global simulation of the cell state in the urban rainwater pipe network: the runoff and non-point source pollution load in the pipe cell in each time step are only determined by the cell states of the two neighboring cells and the previous time step. The formula for calculating the runoff and non-point source pollution load of the pipe cell at each time is as follows: Where: Q p-t+1 and Q p-t Represents the runoff in the pipeline cell at the current moment and the next moment, mm 3 ; P p-t and P p-t+1 Respectively represent the non-point source pollution load in the pipeline cell at the current moment and the next moment, mg; k is the first-order attenuation coefficient, d-1; and are the inflow and outflow of each cell, mm 3 ; and Respectively represent the non-point source pollution load input and output in each cell, mg; The non-point source pollution load of each cell in the entire cellular space at the end of the current moment is obtained, and the calculation is repeated until the entire simulation process is completed.

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