Mountain-front plain type town area water quantity and water quality simulation method considering rainwater grate diversion

Abstract

The invention belongs to the technical field of hydrodynamics and environmental engineering, and provides a mountain-front plain type town area water quantity and water quality simulation method considering rainwater grate diversion, which mainly comprises the steps of basic database construction, water catchment unit division, rainwater grate determination, drainage channel generalization and key process numerical calculation. According to the method, the influence of the surface runoff flow velocity and the terrain gradient on rainwater grate diversion is considered, diversion calculation formulas of different types of rainwater grates are corrected and established, the accuracy of rainwater grate diversion calculation is improved, and the defect that a traditional method subjectively defines the hydraulic connection between surface runoff and a drainage pipe network is overcome; meanwhile, the function presentation of mountain-front plain city land class distribution is considered, a landscape pattern-based earth surface catchment unit division method is established, and the influence of factors such as hydraulic connection and microtopography between land classes on earth surface convergence and pollution output can be accurately represented; and subjectivity and singleness of traditional methods such as Thiessen polygon and road cutting methods are overcome.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of hydrodynamics and environmental engineering, and particularly relates to a simulation method for water quantity and quality of a piedmont plain type urban area considering rainwater grate diversion. BACKGROUND

[0002] The urban river and lake water environment system is a key source of urban matter and energy, and also shoulders the heavy responsibility of reducing and transporting waste of the urban river and lake ecosystem. It is a core carrier supporting the entire urban environment. The urban river and lake water body receives a large amount of tail water discharged by the urban drainage system, and the quality of the tail water plays a decisive role in the environmental quality of the urban river and lake water body, and further deeply relates to the survival and development of the city. Therefore, accurately grasping the key characteristics such as the composition structure, fluctuation range and development trend of the urban river and lake water quantity and quality is of great significance for scientifically guiding the construction and protection of the urban river and lake water environment system.

[0003] Among the current technical means, numerical simulation has become a mainstream method for grasping the characteristics of urban river and lake water quantity and quality due to its clear and explicit mechanism process, quantifiable input variables and output results. It can highly restore the digital mapping and digital twin of the complex physical world, helping management personnel accurately grasp the dynamic changes of the urban river and lake water quantity and quality. For example, the open source code model SWMM (Storm Water Management Model, Storm Water Management Model), as well as the commercial packaged models PCSWMM (Personal Computer Storm Water Management Model, Personal Computer Storm Water Management Model), XPSWMM (XP Storm Water Management Model, XP Storm Water Management Model), Autodesk InfoWorks ICM (Integrated Catchment Software, Integrated Catchment Software) have been widely applied in the global range, providing a large amount of valuable reference basis for urban water environment governance decision-making.

[0004] However, the piedmont plain type town area presents significant complexity in water quantity and quality transport process compared to other town areas. On the one hand, the surface slope in this area is large, and the surface runoff flow rate is fast, which greatly increases the uncertainty of rainwater grate diversion. In this case, the applicability of existing classical weir flow and orifice flow calculation formulas is questionable, which seriously restricts the simulation accuracy of water quantity and quality in the piedmont plain type town area. This is the primary key problem to be solved in water quantity and quality simulation in this area. On the other hand, the land use in the piedmont plain type town area is extremely complex, in addition to the common hardened building road surface, permeable surface green grassland, there are also widely distributed hillside forest land, hillside shrub land, etc. How to scientifically and accurately divide the surface catchment unit to fully reflect the functional characteristics of different land types has become another key problem in water quantity and quality simulation in this area.

[0005] Although existing numerical simulation methods (such as SWMM, InfoWorks ICM, etc.) have been widely applied, they still have significant defects in complex terrain areas:

[0006] Inadequate description of terrain slope influence: existing models mostly ignore the dynamic influence of terrain slope on rainwater grate diversion efficiency, or use simplified slope correction parameters, which makes it difficult to accurately simulate the rainwater grate interception capacity attenuation in mountainous areas (steep slope, fast runoff flow rate), and overestimates the drainage efficiency in low-lying plains (gentle slope, complex flow path), which further causes bias in internal flooding risk assessment or distortion in calculation of non-point source pollution load.

[0007] Terrain adaptability limitation: traditional methods are usually designed for a single terrain type (such as plain cities), lack of universal consideration for different geomorphic features such as piedmont plains, mountains, and hills, and cannot meet the simulation needs of mountain cities "strong runoff erosion-pollutant rapid transport" and plain cities "low-lying water accumulation-non-point source pollution accumulation" at the same time.

[0008] Insufficient application scenarios: existing technologies are difficult to adapt to multiple scenarios such as sponge city planning and drainage system carrying capacity analysis, especially when detailed assessment of terrain-drainage-pollution coupling relationship is needed, the simulation accuracy is limited.

[0009] From the existing research results, the surface runoff and pollutant accumulation and flushing process, and the groundwater drainage network hydrodynamic and water quality process have been relatively mature in their respective fields. The relevant calculation modules have been embedded in various numerical simulation software and have been verified in a large number of practical cases. However, due to the limitations of disciplines, the surface runoff and pollutant accumulation and flushing belong to the field of watershed hydrology, and the groundwater drainage network hydrodynamic and water quality belong to the field of environmental hydraulics. There is still a big research gap in the water quantity and quality interaction process between the two. At the same time, with the transformation of the urban drainage system from extensive surface water collection to grid-based and refined rainwater grating diversion mode, the existing numerical simulation software generally ignores the influence of rainwater grating diversion on the simulation results in the process of pursuing the calculation timeliness, which exposes two major shortcomings of the existing technology:

[0010] First, the rainwater grating diversion calculation method is missing. The urban rainwater grating is an important component of the urban drainage system, which bears the key functions of diverting surface runoff and source pollution. Its structure types include flat grating, vertical grating, and combined grating. The existing simulation methods simply drain the surface runoff and pollutants into the nearest inspection well, which is contrary to the actual situation. In reality, surface runoff and pollutants will flow into low-lying rainwater gratings or drain into the nearest rainwater grating along the road edge. The existing simulation methods are likely to cause the peak value of flow and pollutants to appear early and large due to the omission of this key process.

[0011] Second, the division of surface catchment units is subjective. Surface catchment unit is the smallest calculation unit for urban water environment numerical simulation, which is crucial for surface runoff and source pollution accumulation and flushing calculation. The current commonly used methods such as Thiessen polygon method and road cutting method have many drawbacks. First, roads are subjectively divided into impermeable surfaces and simply included in the surrounding catchment unit, ignoring the key role of roads as flood discharge channels. Second, the division process relies too much on the distribution of inspection wells and fails to fully consider the distribution characteristics of urban functional areas, resulting in the mixing of various land use types and the problem of different parameters with the same effect when determining key parameters. Third, only the distribution of inspection wells is divided, completely ignoring the influence of surface micro-topography on surface runoff and pollutant transport.

[0012] In summary, the existing technology has obvious defects in the simulation of water quantity and quality in the mountainous plain type urban area, especially in the rainwater grating diversion and surface catchment unit division, which needs to be improved by innovative methods. SUMMARY

[0013] In order to overcome the problems of the prior art, the present application proposes a mountain front plain type town area water quantity and quality simulation method considering rainwater grate diversion, which is suitable for various terrain types of town areas (including but not limited to mountain front plain, plain, mountain, hilly land, etc.), is based on GIS, adopts the principle of ecological landscape, comprehensively considers micro-terrain, land use type, land type function and other factors, establishes a water catchment unit division method based on city land type function, and lays a foundation for the connection of water catchment unit and rainwater grate.

[0014] The core feature of the method described in the present application is to finely consider the influence of terrain slope on the rainwater grate diversion process, and to adapt to different regional characteristics by flexibly adjusting the slope related parameters, which can be widely applied to regional / urban waterlogging risk assessment, non-point source pollution load calculation and control, sponge city planning and effect evaluation, drainage system optimization design and other scenes.

[0015] The purpose of the present application is achieved as follows:

[0016] The present application provides a mountain front plain type town area water quantity and quality simulation method considering rainwater grate diversion, comprising the following steps:

[0017] Step 1, construction of basic database:

[0018] Determine the numerical simulation region to be studied, collect spatial data, time data and attribute data in the simulation region; wherein the spatial data includes the range of the numerical simulation region, the division of land use types, the division of town function types, the distribution of drainage pipe networks, the distribution of meteorological stations, the distribution of hydrological monitoring stations, the distribution of water quality monitoring stations and the spatial distribution of rainwater grates; the time data includes meteorological monitoring data, hydrological monitoring data and water quality monitoring data; the attribute data includes land use types, land type and function type, drainage channel information and rainwater grate information of the numerical simulation region.

[0019] Step 2, division of water catchment unit:

[0020] The division of surface water catchment unit based on landscape pattern comprises the following steps:

[0021] S21, based on landscape ecology and distribution characteristics of town functional areas, determine the corridors, patches and matrices of the numerical simulation region;

[0022] S22, based on the division of first-level water catchment units of roads: using the cutting tool of the vector layer in the GIS platform, combining the corridors, patches and matrices of the numerical simulation region determined in S21, taking the spatial distribution characteristics of the main roads of the numerical simulation region, cutting the range of the watershed, and forming a plurality of water catchment units, i.e. first-level water catchment units;

[0023] S23, division of secondary catchment unit based on rainwater grate: for a certain primary catchment unit, according to the distribution of patches inside the primary catchment unit and in combination with the distribution characteristics of rainwater grates, the primary catchment unit is further refined to form secondary catchment units;

[0024] S24, determination of key parameters of catchment unit: the key parameters of the catchment unit include area, width, slope, impervious area, impervious area Manning coefficient, pervious area Manning coefficient, impervious area depression volume and pervious area depression volume.

[0025] Step 3, rainwater grate determination:

[0026] S31, positioning the spatial distribution characteristics of rainwater grates and determining the main information of each rainwater grate: through the basic database constructed in step 1, the position of each rainwater grate is located, the type and water collection range of each rainwater grate are determined, the secondary catchment units covered by the whole are ensured, and the blockage of each rainwater grate is determined;

[0027] The type of the rainwater grate includes flat grate rainwater grate, vertical grate rainwater grate and combined grate rainwater grate;

[0028] S32, establishment of hydraulic connection between rainwater grate and drainage pipe network: through the basic database constructed in step 1, according to the distribution of numerical simulation area drainage pipe network, the hydraulic connection between each rainwater grate and underground drainage pipe network is established, so as to ensure that the runoff and pollution load output by the catchment unit flow into the underground drainage pipe network through the rainwater grate;

[0029] S33, determination of key parameters of rainwater grate: the key parameters include length, height, width and hole number of rainwater grate.

[0030] Step 4, drainage channel generalization:

[0031] The urban drainage channel is divided into surface drainage channel and underground drainage pipe, in order to ensure the overflow water quantity along the trunk road, the drainage channel of the trunk road topography is generalized, which specifically includes:

[0032] S41, generalization of surface drainage channel: the generalization parameters include road width, curb height, road transverse slope, road Manning coefficient, road ditch depth, road ditch width, street rear width and rear slope of surface main road drainage corridor;

[0033] S42, generalization of underground drainage pipe: the underground drainage pipe network is combined and reduced.

[0034] Step 5, numerical calculation of key process:

[0035] The key processes of numerical simulation include surface catchment unit production and confluence and pollutant accumulation and scouring process simulation, rainwater grate diversion and interception process simulation and underground drainage pipe network hydrodynamic and water quality process simulation;

[0036] Wherein, the rainwater grate shunt interception process simulation specifically includes:

[0037] S51, the influence of water flow velocity V on rainwater grate shunt

[0038] (1) considering the influence of water flow velocity V on the weir flow formula:

[0039] (1)

[0040] In the formula: Q weir is the weir flow, C w is the weir flow coefficient, L is the effective weir length, H is the water head on the weir, V is the water flow velocity, g is the acceleration of gravity, is the correction term of the ratio of flow velocity to water head;

[0041] The function relationship of weir flow coefficient C w is:

[0042] (2)

[0043] In the formula: C w0 is the ideal weir flow coefficient, η is the gap rate of the grate, θ is the angle between the water flow direction and the normal of the weir body, B is the weir top submergence ratio, S is the terrain slope, n is the submergence correction coefficient, α and β are the slope correction coefficients.

[0044] (2) considering the influence of water flow velocity V on the orifice flow formula:

[0045] (4)

[0046] In the formula: Q orifice is the orifice flow, C d is the orifice discharge coefficient, A is the effective orifice flow area, h curb is the vertical height from the bottom to the top opening of the vertical grate rainwater grate.

[0047] The function relationship of orifice discharge coefficient C d is:

[0048] (5)

[0049] In the formula: C d is the orifice discharge coefficient, C d0 is the ideal orifice flow coefficient, k shape is the shape correction coefficient, k edge is the edge correction coefficient, C c is the contraction coefficient, and β is the slope correction coefficient.

[0050] The calculation formula of the effective orifice flow area A of the vertical grate orifice is:

[0051] (6)

[0052] In the formula: h open is the effective submergence depth, W inlet is the width of the grate;

[0053] S52, the influence of terrain slope S on rainwater grate distribution

[0054] (1) Weir flow formula considering the influence of slope:

[0055] (7)

[0056] In the formula: Q weir is the weir flow, and alpha is the slope correction coefficient;

[0057] (2) Orifice flow formula considering the influence of slope:

[0058] (8).

[0059] The advantages and beneficial effects of the present application are:

[0060] 1. The mountain front plain type town area water quantity and quality simulation method considering rainwater grate distribution of the present application considers the influence of surface runoff velocity and terrain slope on rainwater grate distribution, corrects and establishes the distribution calculation formula of different types of rainwater grates, improves the accuracy of rainwater grate distribution calculation, and overcomes the subjective definition of the hydraulic connection between surface runoff and drainage pipe network in the traditional method.

[0061] 2. The mountain front plain type town area water quantity and quality simulation method considering rainwater grate distribution of the present application considers the functional presentation of the mountain front plain city land class distribution, establishes a surface catchment unit division method based on landscape pattern, can accurately represent the influence of factors such as hydraulic connection between land classes and microtopography on surface runoff and pollution output, and overcomes the subjectivity and singularity of traditional methods such as Thiessen polygon and road cutting method.

[0062] 3. The mountain front plain type town area water quantity and quality simulation method considering rainwater grate distribution of the present application has good terrain adaptability, and by establishing a numerical simulation method between the physical form of rainwater grate and the flow capacity, it can be widely applied to town area water quantity and quality simulation of mountain front plain, plain, mountain, hilly and other terrains.

[0063] 4. The mountain front plain type town area water quantity and quality simulation method considering rainwater grate distribution of the present application significantly improves the simulation practicability in different application scenarios, including but not limited to fine risk assessment of urban waterlogging, source analysis and load spatial distribution simulation of non-point source pollution, quantitative evaluation of hydrology and water quality effect of sponge city planning scheme, and analysis of urban drainage system carrying capacity. BRIEF DESCRIPTION OF DRAWINGS

[0064] The application will be further described below in conjunction with the accompanying drawings and examples.

[0065] Figure 1 is the overall flow chart of the method for simulating water quantity and quality of a mountain-plain type town area considering rainwater grate diversion according to the embodiment of the application;

[0066] Figure 2 is a structural schematic diagram of different types of rainwater grates according to the embodiment of the application;

[0067] Figure 3 shows the division of a catchment unit of a certain mountain-plain type city typical plot according to the comparative example 2 of the application;

[0068] Figure 4 is a simulation and measurement comparison schematic diagram of the division method of the catchment unit provided by the comparative example of the application and the traditional method. DETAILED DESCRIPTION

[0069] To make the purpose, technical scheme and advantages of the application more clear, the disclosed embodiment will be further described in detail below in conjunction with the drawings. It should be understood that the specific embodiments described herein are only used to explain the application and do not limit the application.

[0070] Embodiment:

[0071] As shown in Figure 1 , the embodiment provides a method for simulating water quantity and quality of a mountain-plain type town area considering rainwater grate diversion, comprising the following steps:

[0072] Step 1, construction of a basic database:

[0073] Determine the numerical simulation area to be studied, and collect spatial data, time data and attribute data in the simulation area.

[0074] The spatial data mainly refers to the geostatistical data of the index value simulation area, including the range of the numerical simulation area, the division of land use types, the division of town function types, the distribution of drainage pipe networks, the distribution of meteorological stations, the distribution of hydrological monitoring stations, the distribution of water quality monitoring stations and the spatial distribution of rainwater grates.

[0075] The time data mainly refers to the monitoring data used for numerical simulation calibration and verification, including meteorological monitoring data, hydrological monitoring data and water quality monitoring data.

[0076] The attribute data mainly refers to attribute information corresponding to the spatial data, including land use types (permeable surface, impervious surface, etc.) of the numerical simulation region, land class and function types (landscape, business, school, natural ecology, etc.), drainage channel information (pipe length, buried depth, material, etc.), and rainwater grate information (rainwater grate type, physical form, water collection capacity, etc.).

[0077] Step 2, division of catchment unit:

[0078] The division of the surface catchment unit based on the landscape pattern specifically includes:

[0079] S21, based on landscape ecology and distribution characteristics of urban functional areas, determine the corridor, patch and matrix of the numerical simulation region.

[0080] The corridor is the traffic road of the numerical simulation region.

[0081] The patch is the catchment unit of the numerical simulation region composed of impervious surfaces including roof patches in building complexes and hardened road patches, and permeable surfaces including green patches.

[0082] The matrix is a large area of patches of the same attribute connected together. For example, impervious surfaces such as hardened road patches and building roof patches in commercial areas, and permeable surfaces such as shrub land patches and grass patches in parks. Generally, the matrix corresponds to the matching urban function of the catchment unit. When the area proportion of patches of the same attribute in a catchment unit exceeds 90%, it is the dominant matrix of this area.

[0083] S22, division of the first catchment unit based on the road: using the cutting tool of the vector layer in the GIS platform, following the principles of uniformity of watershed, integrity of landscape pattern, and consistency of urban function, combining the corridor, patch and matrix of the numerical simulation region determined in S21, cutting the spatial distribution characteristics of the main road of the numerical simulation region to form several catchment units, i.e. the first catchment unit.

[0084] S23, division of the second catchment unit based on the rainwater grate: for a first catchment unit, according to the distribution of patches inside it and combining the distribution characteristics of the rainwater grate, further refine to form a second catchment unit.

[0085] Specifically, in the division process, if the area proportion of a patch is less than 5% of the total area of the catchment unit, the patch needs to be merged with the adjacent patch.

[0086] At the same time, the divided secondary catchment unit needs to be associated with the corresponding rainwater grate to determine the outlet of the secondary catchment unit. For example, the playground and teaching area of the campus have independent rainwater grates and need to be divided independently. The grassland of the building area generally flows into the nearest rainwater grate after converging, and can be merged with the adjacent grassland area as a secondary catchment unit.

[0087] S24, determination of key parameters of catchment unit: The key parameters of the catchment unit include area, width, slope, impervious area, impervious surface Manning coefficient, pervious surface Manning coefficient, impervious surface depression volume, and pervious surface depression volume.

[0088] Step 3, determination of rainwater grate:

[0089] The currently common types of rainwater grates are shown in the following table: Figure 2 The main steps for determining the rainwater grate are as follows:

[0090] S31, positioning the spatial distribution characteristics of the rainwater grate and determining the main information of each rainwater grate: Through the basic database constructed in step 1, the position of each rainwater grate is located, the type and water collection range of each rainwater grate are determined, the secondary catchment unit is ensured to be fully covered, and the blocking condition of each rainwater grate (completely not flowing, local blocking, no blocking, etc.) is determined.

[0091] S32, establishment of hydraulic connection between rainwater grate and drainage pipe network: Through the basic database constructed in step 1, according to the distribution of the numerical simulation area drainage pipe network, the hydraulic connection between each rainwater grate and the underground drainage pipe network is established, and it is ensured that the runoff and pollution load output by the catchment unit flow into the underground drainage pipe network through the rainwater grate.

[0092] S33, determination of key parameters of rainwater grate: According to the type of rainwater grate, the main parameters of rainwater grate generalization include: length, width, and number of holes of flat grate rainwater grate, length and height of vertical grate rainwater grate, length, width, height, and number of holes of combined grate rainwater grate.

[0093] Step 4, drainage channel generalization:

[0094] The urban drainage channel is divided into surface drainage channel and underground drainage pipe. When the rain intensity is less than the drainage capacity of the underground drainage pipe, the rainwater mainly flows in the underground drainage channel. When the rain intensity is greater than the drainage capacity of the pipe network, the water quantity of the drainage pipe network will overflow the surface through the rainwater grate, inspection well, etc. At this time, due to the low elevation of the main road, it becomes a drainage channel, which is called road flood discharge. In the traditional method, only the overflow process of the overflow water on the surface is considered, and the process of road flood discharge is often ignored. Therefore, in order to ensure the overflow water along the main road, the main road terrain is generalized as a drainage channel, which specifically includes:

[0095] S41, surface drainage channel generalization: generalization parameters include road width, curb height, road cross slope, road Manning coefficient, road ditch depth, road ditch width, street back width, back slope. When the surface main road is double-sided, its cross-sectional area needs to be doubled based on the single-sided calculation result.

[0096] S42, underground drainage pipe generalization: in practice, due to the large number of drainage pipe network segments, if not processed for numerical simulation calculation, it will lead to low calculation efficiency, so the underground drainage pipe network needs to be combined and reduced.

[0097] The following principles should be followed when combining and reducing: (1) combine the connected pipe segments with consistent pipe diameter and pipe cross section; (2) on the basis of (1), combine the intersection pipe segments with no change in pipe hydraulic relationship; (3) delete the pipe segments with pipe diameter ≤0.3m or pipe cross section 0.2m 2 .

[0098] The main parameters of the drainage pipe segment generalization include: the pipe diameter of the circular pipe, the bottom width and maximum height of the water passing box culvert, the length of the pipe segment, the Manning coefficient, the inlet bottom offset height, the outlet bottom offset height, the inlet head loss coefficient, and the outlet head loss coefficient.

[0099] Step 5, numerical calculation of key processes:

[0100] This embodiment includes three key processes according to the direction of water flow:

[0101] (1) simulation of surface catchment unit runoff and pollutant accumulation and scouring process;

[0102] (2) simulation of rainwater grate shunt interception process; and

[0103] (3) simulation of underground drainage pipe network hydrodynamic and water quality process.

[0104] Among them, the control equations of key process (1) and key process (3) are relatively mature. The surface runoff calculation formula of key process (1) can refer to water balance, Horton infiltration formula and nonlinear reservoir, and the surface pollutant calculation formula can refer to the cumulative-erosion function. The hydrodynamic process of key process (3) can solve the Saint-Venant equation set, and the water quality process can be based on mass conservation and first-order degradation formula.

[0105] The simulation of rainwater grate shunt interception process in key process (2) is missing in the existing technical numerical calculation process, which specifically includes:

[0106] According to the rainwater grate form classification and hydraulic characteristics, the embodiment innovatively introduces the terrain and slope influence factor, corrects the classical hydraulic formula, and calculates the shunting capacity of various rainwater grates. The common rainwater grate forms and corresponding water flow modes are shown in Table 1.

[0107] Table 1 Common rainwater grate forms and corresponding water flow modes

[0108] Type Hydraulic characteristics Flow pattern Flat grate Flow enters through horizontal grate, similar to weir flow (affected by factors such as grate length, flow area, velocity, slope, clogging) Weir-like flow formula Vertical grate Flow enters through vertical openings, similar to orifice flow (affected by factors such as opening height, flow area, velocity, slope, clogging) Orifice-like formula Combined grate Contains both flat and vertical grates, requires segmented calculation of superimposed effects of weir and orifice flow Weir-like flow + orifice-like formula combination

[0109] In addition to the conventional cognition that the physical form of the rainwater grate will affect the rainwater shunting calculation, the surface flow velocity and slope are also important factors affecting the rainwater grate shunting. The water flow velocity V directly affects the efficiency of weir flow and orifice flow, and high flow velocity may cause the water flow to directly pass over the rainwater grate, reducing the interception efficiency. The terrain slope S is an important source of water flow energy, and the greater the slope, the higher the water flow kinetic energy, which may cause the shunting efficiency to decrease.

[0110] S51, influence of water flow velocity V on rainwater grate shunting

[0111] (1) The weir flow formula considering the influence of water flow velocity V:

[0112] (1)

[0113] In the formula, Q weir is the weir flow, C w is the weir flow coefficient, dimensionless, representing the weir flow efficiency under the comprehensive influence of multiple factors, L is the effective weir length, H is the water head on the weir (m), V is the water flow velocity (m / s), and g is the acceleration of gravity (9.81 m / s²); is the correction term of flow velocity and water head, when V is high, the correction term decreases, and the weir flow rate decreases, when V is low, the correction term is close to 1, and the weir flow rate is not significantly affected.

[0114] The functional relationship of the weir flow coefficient C w is:

[0115] (2)

[0116] In the formula, C w0 is the ideal weir flow coefficient (no gap loss, vertical inflow, no submergence, no flow velocity influence, no slope influence), η is the grate gap rate (0<η≤1), θ is the angle between the water flow direction and the normal of the weir body (0≤θ≤90), B is the weir top submergence ratio (0≤B≤1), S is the terrain slope (dimensionless, usually expressed in percentage or decimal), n is the submergence correction coefficient, and α, β are the slope correction coefficients (generally, α is usually taken as 0.1-0.3, n is 2, and β is 0.2, which can also be calibrated according to experimental data).

[0117] Wherein, the effective weir length L of the flat grate rainwater grate is not the actual physical length, but the effective water width of the grate (related to the grate gap rate), and the calculation formula is shown as formula (3):

[0118] (3)

[0119] In the formula: L eff is the actual length of the grate (m), and η is the grate gap rate (gap area / total area, generally 0.6-0.8).

[0120] (2) Considering the influence of the flow velocity V, the formula of the pseudo-orifice flow is:

[0121] (4)

[0122] In the formula: Q orifice is the pseudo-orifice flow, C d is the orifice discharge coefficient (dimensionless, which represents the flow efficiency parameter when the water flow passes through the orifice), A is the effective flow area of the orifice, and h curb is the vertical height from the bottom to the top opening of the vertical grate rainwater grate.

[0123] h curb is a key parameter for distinguishing between low water level and high water level, which directly affects the flow distribution behavior of the rainwater grate. When the water level is lower than h curb , the water flow mainly enters the rainwater grate through the flat grate part (weir flow). When the water level is higher than h curb , the water flow not only passes through the flat grate part, but also passes through the opening of the vertical grate part (orifice flow) into the rainwater grate.

[0124] The present embodiment comprehensively considers the shape of the orifice, the sharpness of the orifice edge, the water flow contraction effect, the water flow velocity V and the terrain slope S on the orifice flow efficiency, and the function relationship formula of the orifice discharge coefficient C d is:

[0125] (5)

[0126] In the formula: C d is the orifice discharge coefficient, C d0 is the ideal orifice flow coefficient (without shape, edge, contraction, flow velocity and slope influence), k shape is the shape correction coefficient (the shape correction coefficient of the circular orifice is 1.0, the shape correction coefficient of the rectangular orifice is 1.1, the shape correction coefficient of the triangular orifice is 0.9, and the shape correction coefficient of the trapezoidal orifice is 1.05), and k edgeis the edge correction coefficient (the value of the smooth edge correction coefficient is 0.9-0.95, the value of the right angle edge correction coefficient is 0.6-0.7, and the value of the obtuse angle edge correction coefficient is 0.8-0.85), C c is the contraction coefficient, and β is the slope correction coefficient.

[0127] The calculation of the effective flow area A of the strainer type orifice needs to consider the opening height h open , that is, the influence of the effective submergence depth, and the specific calculation formula is:

[0128] (6)

[0129] In the formula, h open is the effective submergence depth (m) (taking min (H, h open )), W inlet is the strainer width (m).

[0130] S52, influence of terrain slope S on rainwater strainer distribution

[0131] (1) weir flow formula considering the influence of slope:

[0132] (7)

[0133] In the formula, Q weir is the weir flow, and α is the slope correction coefficient.

[0134] When S is large, the correction term decreases, and the weir flow distribution decreases; when S is small, the correction term approaches 1, and the weir flow distribution is not significantly affected.

[0135] (2) orifice flow formula considering the influence of slope:

[0136] (8)

[0137] When S is large, the correction term decreases, and the orifice flow distribution decreases; when S is small, the correction term approaches 1, and the orifice flow distribution is not significantly affected.

[0138] S53, comprehensive consideration of the influence of flow velocity V and terrain slope S on rainwater strainer distribution

[0139] The influence of flow velocity V and terrain slope S is simultaneously taken into account in the calculation of rainwater strainer distribution, and the type of actual rainwater strainer and the clogging condition of the rainwater strainer are simultaneously considered, and the calculation formula is as follows:

[0140] (1) flat strainer rainwater strainer distribution calculation formula:

[0141] When the surface water level is low, that is, the water head H on the weir is less than the opening height h curbAt the same time, considering the influence of water flow velocity V and terrain slope S on the weir formula, formula (1) and (7) are combined and processed:

[0142] (9)

[0143] Considering that heavy objects including leaves and debris block the flat grate rainwater grate, the grate gap rate η is modified:

[0144] (10)

[0145] In the formula: η' is the modified grate gap rate, α clog is the blockage coefficient (0≤α clog ≤1, such as 0.3 indicating that the rainwater grate is 30% blocked).

[0146] (2) Vertical grate rainwater grate flow calculation formula:

[0147] When the surface water level is high, that is, the water head H on the weir h curb At the same time, considering the influence of water flow velocity V and terrain slope S on the weir formula, formula (4) and (8) are combined and processed:

[0148] (11)

[0149] If the vertical grate is a porous structure, the total flow is the superposition of single-hole flow:

[0150] (12)

[0151] In the formula: N is the number of orifices, A single is the single-hole area (m 2 ).

[0152] Considering that light objects including plastic bags block the vertical grate rainwater grate, the effective flow area A of the vertical grate orifice in formula (6) is modified:

[0153] (13)

[0154] In the formula: A' is the modified orifice effective flow area;

[0155] (3) Combined grate rainwater grate flow calculation formula:

[0156] The combined grate rainwater grate needs to be calculated in sections to calculate the contribution of weir flow and hole flow, and the total flow is the sum of the two:

[0157] (14)

[0158] When H < h curbWhen H > h, the water flow mainly enters the rainwater grate through the flat grate part curb When H > h, the water flow not only enters the rainwater grate through the flat grate part, but also through the openings of the vertical grate part.

[0159] Comparative Example 1

[0160] In order to explore the influence of the type of rainwater grate on the accuracy of the calculation of the split flow, the following actual case is used for comparative analysis in this comparative example:

[0161] Case scenario setting: the rainwater grate is a combined grate, the water level H = 0.25 m, the flat grate length L = 1.5 m, the vertical grate opening height h curb = 0.2 m, the weir flow coefficient C w = 0.65, the orifice discharge coefficient C d = 0.7, the vertical grate opening area A = 0.1 m², the water flow velocity V = 1.0 m / s, the terrain slope S = 0.05 (5%), the slope correction coefficient α = 0.2, and β = 0.2.

[0162] (1) Calculation using the traditional weir flow and orifice flow calculation formulas

[0163] Traditional weir flow calculation formula:

[0164]

[0165]

[0166] Traditional orifice flow formula calculation formula:

[0167]

[0168]

[0169] Total split flow:

[0170]

[0171]

[0172] (2) Calculation using the above-mentioned modified weir flow and orifice flow calculation formulas of the patent

[0173] Weir flow process calculation using formula (9):

[0174]

[0175] Orifice flow process calculation using formula (11):

[0176]

[0177] Total split flow:

[0178]

[0179]

[0180] It can be seen that the calculation result provided by the patent method is smaller than the traditional calculation method, and the total flow is less than 67%, which is consistent with the actual phenomenon that the rainwater grate has poor water collection effect when the flow rate is large or the slope is large.

[0181] Comparative Example 2:

[0182] This comparative example divides the catchment unit of a certain piedmont plain type city based on landscape pattern, and the catchment unit division of a typical representative plot is shown in Figure 3

[0183] The traditional surface runoff and non-point source material accumulation and scouring calculation formula (for reference: Chen Xuekai, Liu Xiaobo, Dong Fei, etc. Multi-objective optimization control of urban rainwater pumping station based on coupling of SWMM and NSGA-Ⅱ [J]. Journal of Hydraulic Engineering, 2023, 54 (03): 358-368.) and the method described in the embodiment of the present application are used to simulate the regional water quantity and water quality.

[0184] The measured values are compared and analyzed, as shown in Figure 4 It can be seen that compared with the traditional method, the water quantity simulation accuracy is improved by 8%, the chemical oxygen demand in the water quality part is improved by 5%, and the total phosphorus is improved by 9%.

[0185] Finally, it should be noted that the above is only used to illustrate the technical solutions of the present application and not to limit. Although the present application has been described in detail with reference to the preferred arrangement, those skilled in the art should understand that the technical solutions of the present application (such as the use of various formulas, the order of steps, etc.) can be modified or replaced equivalently without departing from the spirit and scope of the technical solutions of the present application.​

Claims

1. A method for simulating water quantity and quality in a prototype urban area in a piedmont plain, considering storm drain diversion, characterized in that, The method includes the following steps: Step 1, Basic Database Construction: The numerical simulation area to be studied is determined, and spatial, temporal, and attribute data are collected within the simulation area. Spatial data includes the watershed extent, land use classification, urban functional classification, drainage network distribution, meteorological station distribution, hydrological monitoring station distribution, water quality monitoring station distribution, and storm drain grate spatial distribution of the numerical simulation area. Temporal data includes meteorological monitoring data, hydrological monitoring data, and water quality monitoring data. Attribute data includes land use type, land category and functional type, drainage channel information, and storm drain grate information of the numerical simulation area. Step 2, water catchment unit division: The division of surface water catchment units based on landscape pattern includes: S21, based on landscape ecology and the distribution characteristics of urban functional zones, determines the corridors, patches, and matrix of the numerical simulation area; S22, First-level catchment unit division based on roads: Using the vector layer cutting tool in the GIS platform, combined with the corridors, patches and matrix of the numerical simulation area determined in S21, the watershed range is cut according to the spatial distribution characteristics of the main roads in the numerical simulation area, forming several catchment units, namely first-level catchment units. S23, Secondary catchment unit division based on storm drain grates: For a certain primary catchment unit, based on the patch distribution within it and combined with the distribution characteristics of storm drain grates, it is further refined into secondary catchment units; S24, Determination of key parameters of the catchment unit: The key parameters of the catchment unit include area, width, slope, impermeable area, Manning coefficient of impermeable surface, Manning coefficient of permeable surface, amount of impermeable surface filling and amount of permeable surface filling; Step 3, Determine the storm drain grate: S31, Locate the spatial distribution characteristics of rainwater grates and clarify the main information of each rainwater grate: Through the basic database constructed in step 1, locate the position of each rainwater grate, clarify the type and water collection range of each rainwater grate, ensure full coverage of the divided secondary water collection units, and clarify the blockage status of each rainwater grate; The types of rain grate include flat grate rain grate, vertical grate rain grate, and combined grate rain grate; S32, Establish the hydraulic connection between the storm drain grate and the drainage network: Based on the basic database constructed in step 1 and the distribution of the regional drainage network in numerical simulation, establish the hydraulic connection between each storm drain grate and the underground drainage network to ensure that the runoff and pollution load output by the water collection unit flows into the underground drainage network through the storm drain grate. S33, Key parameters of rain grate determined: Key parameters include the length, height, width, and number of holes of the rain grate; Step 4, Drainage channel generalization: Urban drainage channels are divided into surface drainage channels and underground drainage pipes. To ensure that overflow water is transported along main roads, the topography of main roads is generalized into drainage channels, specifically including: S41, Generalization of surface drainage channels: Generalization parameters include road width, curb height, road cross slope, road Manning coefficient, ditch depth, ditch width, street rear edge width, and rear edge slope of surface main road drainage corridors. S42, Underground Drainage Pipeline Generalization: Merging and reducing underground drainage pipe networks; Step 5, Numerical calculation of key processes: The key processes of numerical simulation include simulation of runoff generation and confluence and pollutant accumulation and scouring processes in surface water catchment units, simulation of storm drain diversion and interception processes, and simulation of hydrodynamic and water quality processes in underground drainage networks. The simulation of the storm drain sewer interception process specifically includes: S51, The effect of water flow velocity V on rainwater grate diversion (1) Formula for simulated weir flow considering the influence of water flow velocity V: （1） In the formula: Q weir To simulate weir flow, C w Let L be the weir flow coefficient, L be the effective weir length, H be the head above the weir, V be the flow velocity, and g be the acceleration due to gravity. This is a correction term for flow velocity and head ratio; Weir flow coefficient C w The functional relationship is: （2） In the formula: C w0 η is the ideal weir flow coefficient, θ is the grate clearance ratio, θ is the angle between the flow direction and the normal to the weir body, B is the weir crest inundation ratio, S is the topographic slope, n is the inundation correction coefficient, and α and β are the slope correction coefficients. (2) Orifice flow formula considering the influence of water flow velocity V: （4） In the formula: Q orifice For orifice flow simulation, C d Here, h is the orifice discharge coefficient, A is the effective flow area of ​​the orifice, and h is the discharge coefficient. curb The vertical height of the opening from the bottom to the top of the vertical grate-type rain grate; Orifice discharge coefficient C d The functional relationship is: （5） In the formula: C d C is the orifice discharge coefficient. d0 k is the ideal orifice flow coefficient. shape k is the shape correction factor. edge C is the edge correction factor. c β is the shrinkage coefficient, and β is the slope correction coefficient; Formula for calculating the effective flow area A of a vertical grate orifice: （6） Where: h open For effective flooding depth, W inlet Width of the vertical comb; S52, The impact of terrain slope S on storm drain diversion (1) Formula for weir flow considering the effect of slope: （7） In the formula: Q weir For the simulated weir flow, α is the slope correction factor; (2) Orifice flow formula considering the effect of slope: （8）。 2. The method according to claim 1, characterized in that, In step 2, the corridor is the traffic road in the numerical simulation area; The patch is a water catchment unit of the numerical simulation area, which is composed of impermeable surfaces including roof patches and hardened road patches in the building community, and permeable surfaces including green patches. The matrix consists of large areas of patches of the same property connected together.

3. The method according to claim 1, characterized in that, In step 3, S33 determines the key parameters according to the type of rain grate: the length, width, and number of holes of the flat grate, the length and height of the vertical grate, and the length, width, height, and number of holes of the combined grate.

4. The method according to claim 1, characterized in that, In step 5, S51, the formula for calculating the effective weir length L of the flat grate-type rainwater grate is: （3） In the formula: L eff η is the actual length of the grate, and η is the grate gap ratio.

5. The method according to claim 1, characterized in that, Step 5 also includes: S53, comprehensively considering the impact of water flow velocity V and terrain slope S on storm drain diversion. The effects of water flow velocity V and terrain slope S are simultaneously incorporated into the storm drain grate diversion calculation, taking into account the actual type of storm drain grate and the degree of blockage. The calculation formula is as follows: (1) Calculation formula for the diversion of flat grate rainwater: When the surface water level is low, i.e., the head of water above the weir H < h curb When considering the influence of water flow velocity V and topographic slope S on the weir flow formula, formulas (1) and (7) are combined: （9） Considering the potential for heavy objects, including leaves and debris, to clog flat-grate rainwater grates, the grate gap ratio η is adjusted as follows: （10） In the formula: η′ is the corrected grate gap ratio, α clog The congestion coefficient; (2) Calculation formula for the diversion of vertical grate-type rainwater: When the surface water level is high, i.e., the head of water above the weir H > h curb When considering the influence of water flow velocity V and topographic slope S on the weir flow formula, formulas (4) and (8) are combined: （11） If the grate has a porous structure, the total flow rate is the sum of the flow rates of each individual hole: （12） In the formula: N is the number of orifices, A single The area of ​​a single hole; Considering the possibility of lightweight objects, including plastic bags, clogging the vertical grate, the effective flow area A of the vertical grate orifice in formula (6) is modified as follows: （13） In the formula: A′ is the effective flow area of ​​the orifice after correction; (3) Calculation formula for combined grate and rainwater diversion: For combined grate storm drains, the contributions of weir flow and orifice flow need to be calculated segment by segment, with the total component flow being the sum of the two: （14） When H < h curb At this time, water mainly flows into the rainwater grate through the flat grate section; when H > h curb At that time, the water flow not only passes through the flat grate section, but also enters the rain grate through the openings in the vertical grate section.

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