A method for simulating water quantity and quality of a mountain front plain type town area considering rainwater grate diversion

Abstract

The present application belongs to the technical field of hydrodynamics and environmental engineering, and provides a kind of simulation method for water quantity and quality of piedmont plain type town area considering rainwater grate diversion, and the main steps include: basic database construction, catchment unit division, rainwater grate determination, drainage channel generalization and key process numerical calculation.The present application considers the influence of surface runoff velocity and terrain slope on rainwater grate diversion, corrects and establishes the diversion calculation formula of different types of rainwater grates, improves the accuracy of rainwater grate diversion calculation, and overcomes the subjective definition of hydraulic connection between surface runoff and drainage network in traditional method;At the same time, the present application considers the function of piedmont plain city land distribution, establishes a surface catchment unit division method based on landscape pattern, can accurately represent the influence of hydraulic connection between land use types, microtopography and other factors on surface runoff and pollution output, and overcomes the subjectivity and singleness of traditional methods such as thiesen polygon and road cutting method.

Description

Technical Field

[0001] This invention belongs to the field of hydrodynamics and environmental engineering technology, and specifically relates to a method for simulating water quantity and quality in a prototype urban area in a piedmont plain, taking into account storm drain diversion. Background Technology

[0002] Urban river and lake water environment systems, as key sources of urban materials and energy, also bear the heavy responsibility of restoring and transporting waste from urban river and lake ecosystems, serving as the core carriers supporting the entire urban environment. Urban rivers and lakes receive a large amount of wastewater discharged from urban drainage systems; the quality of this wastewater plays a decisive role in the environmental quality of urban river and lake water bodies, thus profoundly impacting the survival and development of cities. Therefore, accurately understanding the key characteristics of urban river and lake water quantity and quality, including their composition, fluctuation range, and development trends, is of great significance for scientifically guiding the construction and protection of urban river and lake water environment systems.

[0003] Among current technological approaches, numerical simulation, with its clear and well-defined mechanisms, quantifiable input variables, and output results, has become the mainstream method for understanding the water quantity and quality characteristics of urban rivers and lakes. It can provide highly accurate digital mapping and digital twins of the complex physical world, helping managers to accurately grasp the dynamic changes in the water quantity and quality of urban rivers and lakes. For example, open-source models such as SWMM (Storm Water Management Model), and commercially packaged models such as PCSWMM (Personal Computer Storm Water Management Model), XPSWMM (XP Storm Water Management Model), and Autodesk InfoWorks ICM (Integrated Catchment Software) have been widely used globally, providing a wealth of valuable reference data for urban water environment governance decisions.

[0004] However, the water quantity and quality transport processes in the piedmont plain prototype urban area exhibit significant complexity compared to other urban areas. On one hand, the area's steep surface slope and rapid surface runoff velocity greatly increase the uncertainty of stormwater grate diversion. Under these circumstances, the applicability of existing classic weir and orifice flow calculation formulas is questionable, severely limiting the accuracy of water quantity and quality simulations in the piedmont plain prototype urban area. This has become the primary key issue that urgently needs to be addressed in water quantity and quality simulations for this region. On the other hand, the landforms in the piedmont plain prototype urban area are extremely complex. In addition to common paved roads and permeable green grasslands, there is a wide distribution of hillside woodlands and hillside shrublands. How to scientifically and accurately delineate surface catchment units to fully reflect the functional characteristics of different land types has become another key challenge in water quantity and quality simulations for this region.

[0005] While existing numerical simulation methods (such as SWMM and InfoWorks ICM) are widely used, they still have significant limitations in areas with complex terrain.

[0006] Insufficient characterization of topographic slope: Existing models often ignore the dynamic impact of topographic slope on storm drain diversion efficiency or use simplified slope correction parameters, making it difficult to accurately simulate the attenuation of storm drain interception capacity in mountainous areas (steep slopes and fast runoff velocities), and easy to overestimate drainage efficiency in low-lying plains (gentle slopes and complex runoff paths), thus causing bias in urban flooding risk assessment or distortion in non-point source pollution load calculation.

[0007] Limited adaptability to terrain: Traditional methods are usually designed for a single terrain type (such as plain cities), lacking universal consideration of different landform features such as piedmont plains, mountains, and hills. They cannot simultaneously meet the simulation requirements of "strong runoff scouring - rapid transport of pollutants" in mountain cities and "low-lying water accumulation - non-point source pollution accumulation" in plain cities.

[0008] Insufficient application scenario coverage: Existing technologies are difficult to adapt to the needs of multiple scenarios such as sponge city planning and drainage system carrying capacity analysis. The problem of limited simulation accuracy is particularly prominent when a detailed assessment of the coupling relationship between terrain, drainage and pollution is required.

[0009] Existing research findings indicate that surface runoff generation and confluence with pollutant accumulation and scouring processes, as well as the hydrodynamic and water quality processes of underground drainage networks, are relatively mature in their respective fields. Related computational modules have been embedded in various numerical simulation software and validated in numerous real-world cases. However, due to disciplinary limitations, surface runoff generation and confluence with pollutant accumulation and scouring fall under the category of watershed hydrology, while the hydrodynamic and water quality processes of underground drainage networks belong to the category of environmental hydraulics. Significant research gaps remain regarding the interaction between these two processes in terms of water quantity and quality. Simultaneously, as urban drainage systems shift from extensive surface water collection to a grid-based, refined storm drain diversion model, existing numerical simulation software, in its pursuit of computational speed, generally neglects the impact of storm drain diversion on simulation results, leading to two major shortcomings in current technology:

[0010] Firstly, there is a lack of calculation methods for storm drain diversion. As a crucial component of urban drainage systems, urban storm drains play a vital role in diverting and intercepting surface runoff and non-point source pollution. Their structural types include flat grates, vertical grates, and combined grates. Existing simulation methods often simply discharge surface runoff and its carried pollutants into nearby manholes, which contradicts reality. In real-world scenarios, surface runoff and pollutants flow into low-lying storm drains or are discharged into nearby storm drains along road edges, depending on the terrain. Existing simulation methods, by omitting this crucial process, are prone to leading to premature and excessively large deviations in flow rate and pollutant peak values.

[0011] Secondly, the delineation of surface catchment units suffers from subjectivity. As the smallest computational unit in urban water environment numerical simulation, the surface catchment unit is crucial for calculating surface runoff generation and non-point source pollution accumulation and scouring. Currently used delineation methods, such as the Thiessen polygon method and road cutting method, have several drawbacks. First, they subjectively classify roads as impermeable surfaces and simply include them in surrounding catchment units, ignoring the crucial role of roads as flood channels. Second, the delineation process relies excessively on the distribution of manholes, failing to fully consider the distribution characteristics of urban functional zones, leading to a mixture of various land use types and the problem of inconsistent parameters having the same effect when determining key parameters. Third, delineation based solely on the distribution of manholes completely ignores the impact of surface micro-topography on surface runoff and pollutant transport.

[0012] In summary, existing technologies have significant shortcomings in simulating water quantity and quality in prototype urban areas of piedmont plains, especially in terms of storm drain diversion and surface catchment unit delineation, and innovative methods are urgently needed to improve them. Summary of the Invention

[0013] To overcome the problems of existing technologies, this invention proposes a method for simulating water quantity and quality in urban areas in piedmont plains that considers storm drain diversion. This method is applicable to urban areas with various terrain types (including but not limited to piedmont plains, plains, mountains, and hills). Based on GIS and employing the principles of ecological landscape science, this method comprehensively considers factors such as micro-topography, land use type, and land function to establish a method for dividing water catchment units based on urban land function, laying the foundation for the connection between water catchment units and storm drains.

[0014] The core feature of the method described in this application is that it meticulously considers the impact of terrain slope on the storm drain diversion process and adapts to the characteristics of different regions by flexibly adjusting slope-related parameters. It can be widely applied to scenarios such as regional / urban flood risk assessment, non-point source pollution load calculation and control, sponge city planning and effect evaluation, and drainage system optimization design.

[0015] The objective of this invention is achieved as follows:

[0016] This invention provides a method for simulating water quantity and quality in a prototype urban area in a piedmont plain, considering storm drain diversion, comprising the following steps:

[0017] Step 1, Basic Database Construction:

[0018] 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 function 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 function type, drainage channel information, and storm drain grate information of the numerical simulation area.

[0019] Step 2, water catchment unit division:

[0020] The division of surface water catchment units based on landscape pattern includes:

[0021] S21, based on landscape ecology and the distribution characteristics of urban functional zones, determines the corridors, patches, and matrix of the numerical simulation area;

[0022] 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.

[0023] 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;

[0024] 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.

[0025] Step 3, Determine the storm drain grate:

[0026] 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;

[0027] The types of rain grate include flat grate rain grate, vertical grate rain grate, and combined grate rain grate;

[0028] 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.

[0029] S33, Key parameters of rain grate determined: Key parameters include the length, height, width, and number of holes of the rain grate.

[0030] Step 4, Drainage channel generalization:

[0031] 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:

[0032] 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.

[0033] S42, Underground Drainage Pipeline Generalization: Merging and reducing underground drainage pipe networks.

[0034] Step 5, Numerical calculation of key processes:

[0035] 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.

[0036] The simulation of the storm drain sewer interception process specifically includes:

[0037] S51, The effect of water flow velocity V on rainwater grate diversion

[0038] (1) Formula for simulated weir flow considering the influence of water flow velocity V:

[0039] (1)

[0040] 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;

[0041] Weir flow coefficient C w The functional relationship is:

[0042] (2)

[0043] 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 submergence ratio, S is the topographic slope, n is the submergence correction coefficient, and α and β are the slope correction coefficients.

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

[0045] (4)

[0046] 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 grate-type rain grate.

[0047] Orifice discharge coefficient C d The functional relationship is:

[0048] (5)

[0049] 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;

[0050] Formula for calculating the effective flow area A of a vertical grate orifice:

[0051] (6)

[0052] Where: h open For effective flooding depth, W inlet Width of the vertical comb;

[0053] S52, The impact of terrain slope S on storm drain diversion

[0054] (1) Formula for weir flow considering the effect of slope:

[0055] (7)

[0056] In the formula: Q weir For the simulated weir flow, α is the slope correction factor;

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

[0058] (8).

[0059] The advantages and beneficial effects of this invention are:

[0060] 1. The water quantity and quality simulation method for urban areas in piedmont plains that considers storm drain diversion described in this invention takes into account the influence of surface runoff velocity and topographic slope on storm drain diversion, and corrects and establishes diversion calculation formulas for different types of storm drains, thereby improving the accuracy of storm drain diversion calculation and overcoming the traditional method's subjective definition of the hydraulic connection between surface runoff and drainage network.

[0061] 2. The water quantity and quality simulation method for urban areas in piedmont plains that considers storm drain diversion described in this invention takes into account the functional presentation of urban land types in piedmont plains and establishes a method for dividing surface runoff units based on landscape patterns. It can accurately characterize the influence of factors such as hydraulic connection between land types and micro-topography on surface runoff generation and pollution output, and overcomes the subjectivity and singularity of traditional methods such as Thiessen polygons and road cutting methods.

[0062] 3. The water quantity and quality simulation method for urban areas in piedmont plains that considers storm drain diversion described in this invention has good terrain adaptability. By establishing a numerical simulation method between the physical form and flow capacity of storm drains, it can be widely applied to the simulation of water quantity and quality in urban areas with various terrains such as piedmont plains, plains, mountains, and hills.

[0063] 4. The water quantity and quality simulation method for urban areas in piedmont plains that considers storm drain diversion described in this invention significantly improves the simulation practicality under different application scenarios, including but not limited to refined risk assessment of urban flooding, source analysis and spatial distribution simulation of non-point source pollution, quantitative assessment of the hydrological and water quality effects of sponge city planning schemes, and analysis of the carrying capacity of urban drainage systems. Attached Figure Description

[0064] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0065] Figure 1 This is the overall flowchart of the water quantity and quality simulation method for a prototype town area in the piedmont plain, which takes into account storm drain diversion, as described in the embodiment.

[0066] Figure 2 These are schematic diagrams illustrating the structures of different types of rainwater grates described in embodiments of the present invention;

[0067] Figure 3 This invention illustrates the water catchment unit division of a typical plot in a prototype city in front of a mountain, as shown in Comparative Example 2.

[0068] Figure 4 This is a schematic diagram comparing the water catchment unit division method provided by the present invention with the traditional method through simulation and actual measurement. Detailed Implementation

[0069] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments disclosed herein will be described in further detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0070] Example:

[0071] like Figure 1 As shown, this embodiment provides a method for simulating water quantity and quality in a prototype urban area in a piedmont plain, considering storm drain diversion, including the following steps:

[0072] Step 1, Basic Database Construction:

[0073] Define the numerical simulation region to be studied, and collect spatial, temporal, and attribute data within the simulation region.

[0074] Spatial data mainly consists of geostatistical data for the numerical simulation area, including the watershed range, land use type classification, urban function type classification, drainage network distribution, meteorological station distribution, hydrological monitoring station distribution, water quality monitoring station distribution, and storm drain spatial distribution of the numerical simulation area.

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

[0076] Attribute data mainly refers to the attribute information corresponding to spatial data, including land use type (permeable surface, impermeable surface, etc.), land category and function type (landscape, business, school, natural ecology, etc.), drainage channel information (pipe length, burial depth, material, etc.) and storm drain grate information (storm drain grate type, physical form, water collection capacity, etc.) of the numerical simulation area.

[0077] Step 2, water catchment unit division:

[0078] The division of surface water catchment units based on landscape pattern includes:

[0079] S21, based on landscape ecology and the distribution characteristics of urban functional areas, determines the corridors, patches, and matrix of the numerical simulation area.

[0080] The corridor refers to the traffic roads in the numerical simulation area.

[0081] The patch is a water catchment unit of a numerical simulation area, which consists of impermeable surfaces including roof patches and hardened road patches within the building complex, and permeable surfaces including green space patches.

[0082] The matrix refers to patches of the same attribute that are connected together over a large area. For example, impermeable surfaces such as paved road patches and building roof patches connected together in a commercial area, and permeable surfaces such as shrubland patches and grassland patches connected together in a park. Generally, the matrix matches the urban function corresponding to the catchment unit. When the area of ​​patches of the same attribute in a certain catchment unit accounts for more than 90%, this is the dominant matrix of this area.

[0083] S22, First-level catchment unit division based on roads: Using the vector layer cutting tool in the GIS platform, following the principles of watershed unity, landscape pattern integrity, and urban function consistency, and combining the corridors, patches, and matrix of the numerical simulation area determined in S21, the watershed range is divided into several catchment units, namely first-level catchment units, based on the spatial distribution characteristics of the main roads in the numerical simulation area.

[0084] 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, secondary catchment units are further refined to form secondary catchment units.

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

[0086] Simultaneously, it is necessary to associate the divided secondary catchment units with the corresponding storm drains to determine the outlets of the secondary catchment units. For example, the playground and teaching areas of a school have independent storm drains and need to be divided independently. Grass areas in residential communities generally flow into the nearest storm drain after runoff collection, and can be merged with adjacent grass areas into a single secondary catchment unit.

[0087] 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.

[0088] Step 3, Determine the storm drain grate:

[0089] Commonly used types of storm drain grates include Figure 2 As shown, the types of rainwater grates include: flat grate rainwater grates, vertical grate rainwater grates, and combined grate rainwater grates. The main steps for determining their types are described below:

[0090] 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 clogging status of each rainwater grate (completely no flow, partial clogging, no clogging, etc.).

[0091] 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.

[0092] S33, Key parameters of rain grate are determined: Based on the type of rain grate, the main parameters of the generalized rain grate include: length, width, and number of holes for flat grate rain grate, length and height for vertical grate rain grate, and length, width, height, and number of holes for combined grate rain grate.

[0093] Step 4, Drainage channel generalization:

[0094] Urban drainage channels are divided into surface drainage channels and underground drainage pipes. When rainfall intensity is less than the drainage capacity of underground drainage pipes, rainwater mainly flows through underground drainage channels. When rainfall intensity exceeds the drainage capacity of the pipe network, water from the drainage network overflows to the surface through storm drains, manholes, etc. Since the main roads are at a lower elevation, they become drainage channels, a phenomenon known as road flooding. Traditional methods only consider the overflow process at the surface, often neglecting the road flooding process. Therefore, to ensure the transport of overflow water along main roads, the topography of main roads is generalized into drainage channels, specifically including:

[0095] S41, Generalization of Surface Drainage Channels: Generalization parameters include road width, curb height, road cross slope, Manning coefficient, ditch depth, ditch width, street rear edge width, and rear edge slope of the surface arterial road drainage corridor. When the surface arterial road has two sides, its cross-sectional area needs to be doubled based on the calculation result for one side.

[0096] S42, Underground Drainage Pipeline Generalization: In reality, due to the large number of drainage pipe network segments, numerical simulation calculations without processing would result in low calculation efficiency. Therefore, it is necessary to merge and reduce the underground drainage pipe network.

[0097] The following principles should be followed when merging and deleting pipe sections: (1) Merge pipe sections that are connected and have the same pipe diameter and cross-section; (2) Based on (1), merge pipe sections that do not change the hydraulic relationship of the pipes; (3) Delete pipe sections with a diameter ≤ 0.3m or a cross-section ≤ 0.2m. 2 The pipe section.

[0098] Circular pipes and culverts are the main cross-sectional shapes of urban drainage pipe networks. The main parameters for generalizing drainage pipe sections include: the diameter of the circular pipe, the bottom width and maximum height of the culvert, the length of the pipe section, the Manning coefficient, the bottom offset height of the inlet, the bottom offset height of the outlet, the head loss coefficient of the inlet, and the head loss coefficient of the outlet.

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

[0100] This embodiment, based on the direction of water flow, includes three key processes in numerical simulation:

[0101] (1) Simulation of runoff generation and pollutant accumulation and scouring process in surface water catchment units;

[0102] (2) Simulation of the storm drain separation and sewage interception process; and

[0103] (3) Simulation of hydrodynamic and water quality processes in underground drainage pipe networks.

[0104] Among them, the governing equations for key processes (1) and (3) are relatively mature. The surface runoff calculation formula for key process (1) can refer to water balance, Horton infiltration formula and nonlinear reservoir, etc., and the surface pollutant calculation formula can refer to the cumulative-scour function. The hydrodynamic process of key process (3) can be solved by solving the Saint-Venant equations, and the water quality process can be based on mass conservation and first-order degradation formula.

[0105] The simulation of the key process (2) of rainwater grate diversion and sewage interception is a missing part in the existing numerical calculation process, which specifically includes:

[0106] Based on the classification of storm drain grate shapes and hydraulic characteristics, this embodiment innovatively introduces topographic and slope influence factors to modify classical hydraulic formulas and calculate the diversion capacity of various storm drain grates. Common storm drain grate shapes and their corresponding flow patterns are shown in Table 1.

[0107] Table 1 Common storm drain grate shapes and their corresponding flow patterns

[0108] type hydraulic characteristics Water flow mode Flat grate rain grate Water flows through horizontal grates, similar to a weir (affected by factors such as grate length, water surface area, flow velocity, slope, and blockage). Simulated weir flow formula Vertical grate rain grate Water flows in through a vertical opening, similar to orifice flow (affected by factors such as opening height, water surface area, flow velocity, slope, and blockage). Orifice Formula Combined grate rain grate It includes both horizontal and vertical grates, requiring segmented calculation of the superposition effect of weir flow and orifice flow. Combination of simulated weir flow and simulated orifice formula

[0109] Besides the commonly recognized influence of the physical morphology of storm drain grates on stormwater diversion calculations, surface flow velocity and slope are also crucial factors affecting storm drain diversion. Flow velocity (V) directly impacts the efficiency of weir and orifice flow; high velocities may cause water to directly bypass the storm drain grate, reducing interception efficiency. Topographic slope (S) is a significant source of water flow energy; a steeper slope results in higher kinetic energy, potentially leading to decreased diversion efficiency.

[0110] S51, The effect of water flow velocity V on rainwater grate diversion

[0111] (1) Formula for simulated weir flow considering the influence of water flow velocity V:

[0112] (1)

[0113] In the formula: Q weir To simulate weir flow, C w denoted as the weir flow coefficient, dimensionless, characterizing the weir flow efficiency under the combined influence of multiple factors, where L is the effective weir length, H is the head above the weir (m), V is the flow velocity (m / s), and g is the gravitational acceleration (9.81 m / s²). This is a correction term for flow velocity and head; when V is high, the correction term... As V decreases, the weir flow distribution decreases. When V is low, the correction term is close to 1, and the weir flow distribution is not significantly affected.

[0114] Weir flow coefficient C w The functional relationship is:

[0115] (2)

[0116] In the formula: C w0 The ideal weir flow coefficient is defined as follows: η is the grate gap ratio (0 < η ≤ 1), θ is the angle between the flow direction and the weir normal (0 ≤ θ ≤ 90°), B is the weir crest submergence ratio (0 ≤ B ≤ 1), S is the topographic slope (dimensionless, usually expressed as a percentage or decimal), n is the submergence correction factor, and α and β are the slope correction factors (generally, α is usually taken as 0.1-0.3, n is 2, and β is 0.2, but can also be calibrated according to experimental data).

[0117] Among them, the effective weir length L of the flat grate rainwater grate is not the actual physical length, but the effective water passage width of the grate (related to the grate gap ratio), and the calculation formula is shown in equation (3):

[0118] (3)

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

[0120] (2) Orifice flow formula considering the influence of water flow velocity V:

[0121] (4)

[0122] In the formula: Q orifice For orifice flow simulation, C d Here, A is the orifice discharge coefficient (dimensionless, a parameter characterizing the flow efficiency of water passing through the orifice), and h is the effective flow area of ​​the orifice. curb The vertical height of the opening from the bottom to the top of the grate-type rain grate.

[0123] h curb It is a key parameter for distinguishing between low and high water levels, directly affecting the diversion behavior of storm drain grates. When the water level is below h... curb At this time, the water flow mainly enters the storm drain grate through the flat grate section (weir flow), and when the water level is higher than 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 (orifice flow) of the vertical grate section.

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

[0125] (5)

[0126] In the formula: C d C is the orifice discharge coefficient. d0 k is the ideal orifice flow coefficient (without the influence of shape, edge, contraction, velocity, or slope). shape For shape correction factors (1.0 for circular orifices, 1.1 for rectangular orifices, 0.9 for triangular orifices, and 1.05 for trapezoidal orifices), k edgeC represents the edge correction factor (0.9~0.95 for smooth edges, 0.6~0.7 for right angle edges, and 0.8~0.85 for obtuse angle edges). c β is the contraction coefficient, and β is the slope correction coefficient.

[0127] The calculation of the effective flow area A of a vertical grate orifice needs to take into account the opening height h. open The effect of effective flooding depth is calculated using the following formula:

[0128] (6)

[0129] Where: h open For the effective flooding depth (m) (take min(H, h)), open W inlet Width of the vertical grate (m).

[0130] S52, The impact of terrain slope S on storm drain diversion

[0131] (1) Formula for weir flow considering the effect of slope:

[0132] (7)

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

[0134] When S is large, the correction term Decreasing the flow rate reduces the weir flow distribution; when S is small, the correction term is close to 1, and the weir flow distribution is not significantly affected.

[0135] (2) Orifice flow formula considering the effect of slope:

[0136] (8)

[0137] When S is large, the correction term As S decreases, the orifice flow split rate decreases. When S is small, the correction term is close to 1, and the orifice flow split rate is not significantly affected.

[0138] S53, comprehensively considering the impact of water flow velocity V and terrain slope S on storm drain diversion.

[0139] 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:

[0140] (1) Calculation formula for the diversion of flat grate rainwater:

[0141] When the surface water level is low, i.e., the head of water above the weir H < h curbWhen considering the influence of water flow velocity V and topographic slope S on the weir flow formula, formulas (1) and (7) are combined:

[0142] (9)

[0143] 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:

[0144] (10)

[0145] In the formula: η′ is the corrected grate gap ratio, α clog The congestion coefficient (0≤α) clog ≤1, such as 0.3, indicates that the rain grate is 30% blocked.

[0146] (2) Calculation formula for the diversion of vertical grate-type rainwater:

[0147] 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:

[0148] (11)

[0149] If the grate has a porous structure, the total flow rate is the sum of the flow rates of each individual hole:

[0150] (12)

[0151] In the formula: N is the number of orifices, A single The area of ​​a single hole (m²) 2 ).

[0152] 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:

[0153] (13)

[0154] In the formula: A′ is the effective flow area of ​​the orifice after correction;

[0155] (3) Calculation formula for combined grate and rainwater diversion:

[0156] 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:

[0157] (14)

[0158] When H < h curbAt 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.

[0159] Comparative Example 1:

[0160] To investigate the impact of storm drain grate type on the accuracy of diversion calculations, this comparative example uses the following real-world case for comparative analysis:

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

[0162] (1) Calculations were performed using 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 flow rate:

[0170]

[0171]

[0172] (2) The calculation is performed using the modified formulas for simulated weir flow and simulated orifice flow from the above embodiments of this patent.

[0173] The weir flow process is calculated using formula (9):

[0174]

[0175] The orifice flow process is calculated using formula (11):

[0176]

[0177] Total flow rate:

[0178]

[0179]

[0180] It can be seen that, compared with traditional calculation methods, the calculation results provided by this patented method are too small, with the total flow rate being 67% less. This is consistent with the actual situation where the rainwater grate has poor water collection effect when the flow velocity is high or the slope is steep.

[0181] Comparative Example 2:

[0182] This comparative example divides a prototype city in a piedmont plain into catchment units based on landscape pattern. The catchment unit division of its typical representative plots is as follows: Figure 3 As shown.

[0183] The traditional surface runoff generation and runoff and non-point source material accumulation-scour calculation formulas (see: Chen Xuekai, Liu Xiaobo, Dong Fei, et al. Multi-objective optimization control of urban stormwater pumping stations based on SWMM and NSGA-II coupling [J]. Journal of Hydraulic Engineering, 2023, 54 (03): 358-368.) and the method described in the embodiments of this application were used to simulate regional water quantity and water quality.

[0184] Comparative analysis using measured values, such as Figure 4 As shown, compared with the traditional method, the accuracy of water quantity simulation has been improved by 8%, and in terms of water quality, chemical oxygen demand has increased by 5% and total phosphorus by 9%.

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

Claims

1. A method for simulating water quantity and quality in a piedmont plain type urban area considering rainwater grate diversion, characterized by, The method comprises the following steps: Step 1, basic database construction: Determine the numerical simulation area to be studied, collect spatial data, time data and attribute data in the simulation area; wherein the spatial data includes the basin range of the numerical simulation area, the land use type division, the urban function type division, the drainage pipe network distribution, the meteorological station distribution, the hydrological monitoring station distribution, the water quality monitoring station distribution and the rainwater grate spatial distribution; the time data includes meteorological monitoring data, hydrological monitoring data and water quality monitoring data; the attribute data includes the land use type of the numerical simulation area, the land type and function type, the drainage channel information and the rainwater grate information; Step 2, division of catchment unit: Based on the landscape pattern, the surface catchment unit is divided, which specifically comprises: S21, based on the distribution characteristics of landscape ecology and urban function area, the corridor, patch and matrix of the numerical simulation area are determined; S22, based on the first catchment unit division of the road: using the cutting tool of the vector layer in the GIS platform, combining the corridor, patch and matrix of the numerical simulation area determined in S21, taking the spatial distribution characteristics of the main road of the numerical simulation area, cutting the basin range to form a plurality of catchment units, i.e. the first catchment unit; S23, based on the second catchment unit division of the rainwater grate: for a first catchment unit, according to the distribution of the patch inside it, and combining the distribution characteristics of the rainwater grate, the second catchment unit is further refined; 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 storage and pervious surface depression storage; Step 3, rainwater grate determination: S31, positioning the spatial distribution characteristics of the rainwater grate and determining the main information of each rainwater grate: positioning the position of each rainwater grate through the basic database constructed in step 1, determining the type, water collection range of each rainwater grate, ensuring that the second catchment unit is fully covered, and determining the blockage of each rainwater grate; The type of the rainwater grate includes flat grate rainwater grate, vertical grate rainwater grate and combined grate rainwater grate; 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 drainage pipe network in the numerical simulation area, the hydraulic connection between each rainwater grate and the underground drainage pipe network is established, to ensure that the runoff and pollution load output by the catchment unit flow into the underground drainage pipe network through the rainwater grate; S33, determination of key parameters of rainwater grate: the key parameters include the length, height, width and hole number of the rainwater grate; Step 4, drainage channel generalization: The urban drainage channel is divided into surface drainage channel and underground drainage pipe, in order to ensure the overflow water along the main road, the drainage channel of the main road is generalized, which specifically comprises: S41, generalization of surface drainage channel: the generalization parameters include the road width of the surface main road drainage corridor, the road curb height, the road transverse slope, the road Manning coefficient, the road ditch depth, the road ditch width, the street rear width and the rear slope; S42, generalization of underground drainage pipe: the underground drainage pipe network is combined and reduced; Step 5, numerical calculation of key processes: The key processes of the numerical simulation include surface catchment unit runoff and pollutant accumulation and wash-off process simulation, rainwater grate separation and interception process simulation, and underground drainage network hydrodynamic and water quality process simulation. The rainwater grate separation and interception process simulation specifically includes: S51, influence of water flow velocity V on rainwater grate separation (1) Weir flow formula considering the influence of water flow velocity V: （1） wherein: Q weir C is the weir flow coefficient, L is the effective weir length, H is the water head on the weir, V is the flow velocity, g is the gravitational acceleration, w C is the weir flow coefficient, L is the effective weir length, H is the water head on the weir, V is the flow velocity, g is the gravitational acceleration, is a correction term for the ratio of flow velocity to water head. Weir flow coefficient C w The functional relationship is: （2） where C w0 is the ideal weir coefficient, η is the grate gap ratio, 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, 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 given by （5） where: C d is the orifice discharge coefficient, C d0 is the ideal orifice flow coefficient, k shape is the shape correction factor, k edge is the edge correction factor, C c is the contraction coefficient, β is the slope correction factor; Calculation formula of effective flow area A of vertical grate orifice: （6） wherein: h open W is the effective flooding depth inlet is the width of the rake S52, influence of terrain slope S on rainwater grate separation (1) Weir flow formula considering the influence of slope: （7） where: Q weir is the weir flow, and a is the slope correction factor. (2) Orifice flow formula considering the influence of slope: （8）。 2. The method of claim 1, wherein, In step 2, the corridor is a traffic road in the numerical simulation area. The patch is composed of impervious surfaces including roof patches and hardened road patches in building complexes, and pervious surfaces including green patches, which together form a catchment unit in the numerical simulation area. The matrix is a large area of patches with the same attribute connected together.

3. The method of claim 1, wherein, In step 3, S33 determines the key parameters according to the type of rainwater grate: 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.

4. The method of claim 1, wherein, In step 5, S51, the calculation formula of effective weir length L of flat grate rainwater grate is: （3） where: L eff is the actual length of the bars and η is the bar gap ratio.

5. The method of claim 1, wherein, Step 5 also includes: S53, comprehensive consideration of the influence of water flow velocity V and terrain slope S on rainwater grate separation The influence of water flow velocity V and terrain slope S on rainwater grate separation is considered simultaneously, and the type of actual rainwater grate and the clogging condition of rainwater grate are also considered. The calculation formula is as follows: (1) Flat grate rainwater grate separation calculation formula: When the local water level is low, that is, the water head H on the weir < h curb When the local water level is low, that is, the water head H on the weir < h curb When the local water level is low, that is, the water head H on the weir < h curb When the local water level is low, that is, the water head H on the weir < h curb When the local water level is low, that is, the water head （9） Considering the clogging of flat grate rainwater grate by heavy objects such as leaves and debris, the grate gap rate η is modified: （10） wherein: η' is the corrected screen opening ratio, α clog is the plugging coefficient; (2) Vertical grate rainwater grate separation calculation formula: When the local water level is high, that is, the water head H on the weir > h curb When the local water level is high, that is, the water head H on the weir > h curb When the local water level is high, that is, the water head H on the weir > h curb When the local water level is high, that is, the water head H on the weir > h curb When the local water level is high, that is, the water head （11） If the vertical grate is a multi-hole structure, the total flow is the superposition of single-hole flow: （12） where: N is the number of orifices, A single is the area of a single orifice; Considering the clogging of vertical grate rainwater grate by light objects such as plastic bags, the effective flow area A of vertical grate orifice in formula (6) is modified: （13） Where: A' is the modified orifice effective flow area; (3) Combined grate rainwater grate separation calculation formula: Combined grate rainwater grate needs to calculate the contribution of weir flow and orifice flow in sections, and the total flow is the sum of the two: （14） When H < h curb , the water flow mainly enters the rainwater grate through the flat grate part; when H > h curb , the water flow not only enters the rainwater grate through the flat grate part, but also through the openings of the vertical grate part.

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