Urban drainage pipe network load capacity calculation and early warning method

Abstract

The invention discloses an urban drainage network load capacity calculation and early warning method, which comprises the following steps of: a, analyzing the characteristics of regional rainfall and the current situation of a drainage network system, and providing current situation analysis and data support for establishing a drainage network model and formulating an emergency disposal scheme; b, a drainage pipe network model is established, a powerful tool is provided for operation condition analysis and system bottleneck identification of an urban drainage pipe network system, and meanwhile support is provided for optimization decision making of an urban drainage emergency treatment plan; c, an urban drainage emergency treatment plan is formulated, support is provided for urban emergency rescue and disaster relief when over-standard rainfall comes, so that loss of rainstorm disasters is reduced to the minimum, and according to the urban drainage network load capacity calculation and early warning method, a network graph theory is adopted to create a network construction inverted-order arrangement matrix algorithm, and the calculation and early warning of the load capacity of the urban drainage network are achieved. Programmed arrangement of the convergence sequence of the drainage pipe network is achieved, and innovation and practicability are achieved in the aspects of pipe network graph theory analysis and drainage pipe section hourly flow distribution calculation.

Description

Technical Field

[0001] The present invention relates to the technical field of early warning methods for urban zoned rainwater drainage pipe networks, and in particular to a method for calculating and early warning the load capacity of urban drainage pipe networks. Background Art

[0002] The urban drainage network is a huge pipe system, which is distributed in a three-dimensional cross-network underground. The system structure is complex, and the amount of data and information generated by engineering design, engineering construction, system operation and maintenance management is very large. The data information management and safe operation and maintenance of the drainage network system is a very complex and arduous task.

[0003] The National New Urbanization Plan (2014-2020) proposes to promote the construction of smart cities, develop digital urban management, promote the establishment of a unified urban geographic space information platform and building (structure) database, build a smart city public information platform, and coordinate the digitalization and precision of municipal infrastructure management such as urban planning, land use, urban pipe network, landscaping, and environmental protection. Smart water affairs are an important part of smart cities. Through online monitoring equipment such as data acquisition instruments, water quality and water pressure meters, the operating status of urban water supply and drainage systems is perceived in real time, forming an "urban water affairs Internet of Things", managing the entire production, management and service process of the water affairs system in a more refined and dynamic way, and realizing the "smart management" of urban facilities.

[0004] With the application and popularization of computer software systems such as Geographic Information System (GIS), Global Positioning System (GPS) and Management Information System (MIS) and hardware equipment such as telemetry and teletransmission, the management and operation information management technology and application software of drainage pipe network have been continuously developed and improved, covering pipe network GIS, SCADA, real-time operation simulation, automatic management and optimized operation, etc. By using advanced GIS technology, SCADA technology and mathematical models, the urban drainage system can be rationally planned, online data detection and real-time operation management can be carried out to achieve safe and efficient operation management of the drainage pipe network system. By applying computer network technology, communication technology, intelligent control technology, Internet of Things and other information technologies, a "drainage pipe network information management platform" is developed to realize the digitalization, networking and spatial visualization of the safety production monitoring and management of the drainage pipe network. Through the effective operation of the platform, the data of pipeline equipment can be monitored in real time, which plays an important role in deeply and accurately grasping the real-time status of drainage pipe network assets and operation capacity, implementing pipe network accident investigation and unblocking congestion, and pipe network maintenance and transformation. To this end, we propose a method for calculating and warning the load capacity of urban drainage pipe network. Summary of the invention

[0005] In view of the shortcomings of the prior art, the present invention proposes a design method for early warning of urban rainwater drainage pipe networks. Through the monitoring data of the drainage pipe network and the calculation of the hydraulic model of the pipe network, the problem of the difficulty in evaluating the load capacity of the rainwater drainage pipe network itself is solved.

[0006] To achieve the above object, the present invention provides the following technical solution: a method for early warning of load of urban drainage pipe network, comprising the following steps:

[0007] a. Analyze the characteristics of regional rainfall and the current status of the drainage network system, and provide current status analysis and data support for establishing a drainage network model and formulating emergency response plans;

[0008] b. Establish a drainage network model to provide a powerful tool for analyzing the operating conditions of the urban drainage network system and identifying system bottlenecks, while providing support for the optimization decision-making of urban drainage emergency response plans;

[0009] c. Formulate an emergency plan for urban drainage to provide support for urban rescue and disaster relief when excessive rainfall occurs, thereby minimizing the losses caused by rainstorm disasters.

[0010] A method for calculating the load capacity of a town drainage network comprises the following steps:

[0011] Step 1: Establish a model of urban rainwater drainage network;

[0012] Step 2: Design a water model;

[0013] Step 3: Establish a mathematical model of the rainwater drainage network;

[0014] Step 4: Determine overflow and water accumulation.

[0015] Preferably, the method for designing a water model comprises the following steps:

[0016] Step 21, drainage geometric expression method design, realized by pipe network diagram, the pipe network diagram is derived from the shape of pipe network layout;

[0017] Step 22: Design of the pipe network association matrix, setting up a single drainage pipe network, defining the structural characteristics of the pipe network through data, and converting it into other types of pipe network model data;

[0018] Step 23, model path matrix design, using the path numbers of all water flow pipe sections in the pipe network, to generate a set matrix including all water flow path pipe sections for the hydraulic mathematical model of the drainage pipe network.

[0019] Preferably, the method for establishing a mathematical model of a rainwater drainage network comprises the following steps:

[0020] Step 31, setting of rainfall process line, the simulated rainfall process adopted includes two types, one is to adopt synthetic rainfall process, the other is to adopt measured or historical rainfall process;

[0021] Step 32, hydraulic calculation, the non-full flow in the circular pipe has a free surface, and relies on the gravity formed by the bottom slope of the pipe to flow from the high end to the low end, and determine the hydraulic relationship between the flow rate, flow velocity, cross-sectional size, fullness and slope of the pipe;

[0022] Step 33: Calculate critical water depth.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] The present invention adopts network graph theory in establishing the real-time model module of the drainage network operation status, creates the above-mentioned network structure reverse arrangement matrix algorithm, realizes the programmed arrangement of the drainage network confluence order, is innovative and practical in the theoretical analysis of network graphs and the calculation of hourly flow distribution of drainage pipe sections, and establishes a new graph sorting calculation method for drainage network model calculation.

[0025] The drainage network model includes two parts: node flow and segment flow calculation. The drainage network model can reproduce the historical and current operation status of the drainage network, and can also predict the operation status of the drainage network system in the future. Finally, the modeling results are processed and analyzed as a scientific basis for management decisions. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a simplified diagram of the drainage network;

[0027] Figure 2 This is a schematic diagram of the drainage network;

[0028] Figure 3 Composite rainfall hydrograph for Chicago;

[0029] Figure 4 It is a schematic diagram of the fullness of a circular pipe;

[0030] Figure 5 This is the hydraulic characteristic diagram of a non-full flow circular pipe. DETAILED DESCRIPTION

[0031] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0032] A method for early warning of urban drainage pipe network load, comprising the following steps:

[0033] a. Analyze the characteristics of regional rainfall and the current status of the drainage network system, and provide current status analysis and data support for establishing a drainage network model and formulating emergency response plans;

[0034] b. Establish a drainage network model to provide a powerful tool for analyzing the operating conditions of the urban drainage network system and identifying system bottlenecks, while providing support for the optimization decision-making of urban drainage emergency response plans;

[0035] c. Formulate an emergency plan for urban drainage to provide support for urban rescue and disaster relief when excessive rainfall occurs, thereby minimizing the losses caused by rainstorm disasters.

[0036] A method for calculating the load capacity of a town drainage network, the specific steps are as follows:

[0037] Step 1: Establish a model of urban rainwater drainage network:

[0038] Implementation example:

[0039] Import the basic data measured on site into the facility database through the formulated table

[0040]

[0041]

[0042]

[0043]

[0044] Step 2: Design water model:

[0045] 2.1 Design of drainage geometry expression method

[0046] Geometric expression is a visual method, usually used in manual analysis of pipe network problems. Since the pipe network diagram is derived from the shape of the pipe network layout, it is easy to cause confusion in concepts, so be sure to pay attention to the difference. Since the pipe network diagram only represents the topological relationship of the pipe network, there is no need to pay attention to the structural attributes of elements such as the location of the node and the length of the pipe segment. In other words, the location of the node and the length of the pipe segment in the pipe network diagram do not have to be consistent with the actual situation. The turning or bending pipe segment can also be drawn as a straight line, and the pipe segment can also be lengthened or shortened, as long as the relationship between the node and the pipe segment remains unchanged.

[0047] Figure 1 It is a geometric representation of a drainage network diagram.

[0048] The collection representation of a graph is:

[0049] Suppose there is a node set V = {v1, v2, v3, ... vn} and a pipe segment set E = {e1, e2, e3, ... em}, and any pipe segment ek = (vi, vj) ∈ E is associated with nodes vi ∈ V and vj ∈ V, then the set V and E form a pipe network graph, denoted as G (V, E). N = |V| is the number of nodes in the pipe network graph, M = |E| is the number of pipe segments in the pipe network graph, nodes vi and vj are called the endpoints of the pipe segment ek, the pipe segment ek = (vi, vj) is said to be associated with the node vi or vj, and the nodes vi and vj are called adjacent nodes.

[0050] by Figure 1 Taking the pipe network diagram shown in the figure as an example, the set of the pipe network diagram is represented by G(V, E), and the node set is:

[0051] V={1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12);

[0052] The pipe segment collection is:

[0053] E={(1,2), (2,3), (3,4), (4,5), (5,6), (6,7), (8,3), (9,10), (10,5), (11,12), (12,10)}.

[0054] The number of nodes in the pipe network diagram is N(G)=12, and the number of pipe sections is M(G)=11.

[0055] For the pipe network graph G(V, E), the set of pipe segments associated with node v is called the association set of node v, denoted by S(v), or simply Sv, which is used to represent the association relationship between nodes and pipe segments in the pipe network graph.

[0056] 2.2 Design of Pipeline Network Association Matrix and Model Path Matrix

[0057] Suppose a simple drainage network is Figure 2 As shown, the number of pipe network sections NP = 9, and the number of nodes NN = 10. The arrows indicate the direction of water flow, and node 7 is the drainage outlet.

[0058] The pipe segment data is shown below.

[0059]

[0060] Node catchment area (ha) data: Aj[NN]={0.15, 0.15, 0.15, 0.15, 0.15, 0.15, 0.15, 0.15, 0.15};

[0061] Node ground elevation (m) data: Hj[NN] = {5.24, 5.19, 5.18, 5.00, 5.21, 5.20, 5.20, 5.12, 5.13, 5.18};

[0062] The above data defines the structural characteristics of the pipeline network and can be converted into other types of pipeline network model data.

[0063] From the starting point and end point number data I0[k] and J0[k] of the pipe segment, a characteristic data matrix defining each node can be converted to express the position and role of each node in the pipe network. The matrix is ​​named MNP[NN][i]. The first column is the node number, the second column is the number of pipe segments flowing into the node, the third column is the number of pipe segments flowing out of the node, and the fourth column and subsequent columns are the numbers of the pipe segments flowing into the node, forming all the data for generating MNP[NN][i].

[0064] Depend on Figure 2 The following matrix data can be obtained:

[0065]

[0066] The above output results show that nodes 0, 8 and 9 have no inflow pipe segments, which means they are the starting nodes of the pipe network and each has an outflow pipe segment; node 6 has 2 inflow pipe segments, namely the 5th and 8th pipe segments, and 1 outflow pipe segment; node 7 is the outlet node, with 2 inflow pipe segments, namely the 6th and 7th pipe segments, and 0 outflow pipe segments.

[0067] In the same way, the start and end number data I0[k] and J0[k] of the pipe segment can be used to find all the start node numbers in the pipe network, and generate a one-dimensional pipe network start node data matrix, named Mstart[i], which is used for the mathematical model of the pipe network. There are 3 start nodes in the pipe network, coded as 0, 8 and 9 respectively.

[0068] In order to find the flow direction and flow path in the drainage network, the path numbers of all the flow pipe segments in the network are used to generate a set matrix including all the flow path segments, named Mbranch[i][j], which is used in the hydraulic mathematical model of the drainage network. Figure 2 The data of Mbranch[i][j] matrix can be obtained as follows:

[0069]

[0070] The above results show that there are three water flow paths in the pipe network. The pipe segment sets of each path are [6, 5, 4, 3, 2, 1, 0], [7] and [8] respectively, and -99 means that there is no pipe segment.

[0071] Step 3: Establish a mathematical model of the rainwater drainage network:

[0072] By establishing a drainage network model to calculate and simulate the operation status of the drainage system, we can understand the operation status of the drainage network system under different drainage conditions and flow loads, find the causes of accidents and system bottlenecks in the drainage network system, find the location of overloaded pipe sections, and provide a scientific basis for network operation management and maintenance transformation. By simulating the network system under different rainstorm intensities, we can evaluate the drainage capacity of the existing network and pumping station to ensure that the existing drainage capacity can play a timely and reliable role. At the same time, we can identify the locations where waterlogging is prone to occur in the drainage system, analyze the causes of urban waterlogging, strengthen safety protection, and fundamentally establish a scientific and complete drainage network intelligent management system.

[0073] 3.1 Setting of rainfall process line

[0074] The simulated rainfall processes used generally include two types, one is the synthetic rainfall process, and the other is the measured or historical rainfall process. The Chicago process line model is a rainfall process synthesis method that combines the rainstorm intensity formula with the rain peak coefficient. If the rainstorm intensity formula is:

[0075]

[0076] The total rainfall during the period td is:

[0077] Then the instantaneous rainfall intensity at time t is:

[0078] This is an instantaneous rainfall process line with the same average rainfall intensity, and a rain peak is formed at a ratio r of the duration after the start of rainfall. When the rainfall duration is:

[0079] t=ta+tb, where tb is the duration of rainfall before the peak and ta is the duration of rainfall after the peak.

[0080]

[0081] In the Chicago application, r = 0.375.

[0082] Substituting formula 2 into formula 1, we have

[0083] and

[0084] In the calculation process, tb and ta are both time values ​​from the rain peak. The closer to the rain peak, the larger the i value.

[0085] Suppose the rainstorm intensity formula for a city is

[0086]

[0087] The rainfall duration is 120 minutes, the peak coefficient is 0.4, and the return period is 1 year. The curve form of the rainfall process data is as follows Figure 3 shown.

[0088] 3.2 Hydraulic calculation

[0089] The rainwater drainage network in the city generally adopts full pipe flow design, and the sewage drainage pipe generally requires non-full pipe flow design. However, during the operation of the rainwater drainage network, it is in a non-full pipe flow state most of the time, and its engineering design and operation state require hydraulic calculations of non-full pipe flow.

[0090] The non-full flow in a circular pipe has a free surface and flows from the higher end to the lower end by gravity formed by the bottom slope of the pipe. The purpose of hydraulic calculation of non-full flow pipe is to determine the hydraulic relationship between the flow rate, flow velocity, cross-sectional size, fullness and slope of the pipe, and to obtain a scientific and reasonable engineering design plan.

[0091] Manning introduced the roughness coefficient n of the pipe, called the Manning roughness coefficient, and gave the calculation formula of the Xie Cai coefficient C, called the Manning formula, which is suitable for hydraulic calculations of open channels, non-full pipe flows or rougher pipes. The formula is:

[0092]

[0093] Where, C is the Scheherazade coefficient; R is the hydraulic radius; n is the Manning roughness coefficient.

[0094] Substituting the above formula into Xie Cai's formula,

[0095]

[0096] get:

[0097]

[0098] Where h f ―head loss along the way (m); v―average flow velocity in the water-passing section (m / s); l―length of the pipeline (m).

[0099] Common pipe Manning roughness coefficient n

[0100]

[0101] Let i = hf / l, we can get:

[0102]

[0103] This formula is widely used in the hydraulic calculation formula for uniform flow in open channels and non-full pipes.

[0104] Substitute into the canal flow formula:

[0105] q=A·v

[0106] have to:

[0107]

[0108] Where q is the flow rate in the pipe; A is the cross-sectional area of ​​the water flow (m2); I is the hydraulic gradient, which is the bottom slope of the pipe for uniform flow.

[0109] like Figure 4 As shown in the figure, the diameter of the circular pipe is D, the water depth in the pipe is y, and the filling degree is y / D. From geometry, we can get the angle calculation formula from the center of the pipe to the two ends of the water surface line:

[0110]

[0111] Where θ is in radians. Or

[0112]

[0113] Water flow cross-sectional area:

[0114]

[0115] Wet week:

[0116]

[0117] Hydraulic radius:

[0118]

[0119] Assuming that the cross-sectional area, hydraulic radius, flow rate and flow velocity of full pipe flow are A0, R0, q0 and v0 respectively, then A0=πD 2 / 4 and R0=D / 4, and

[0120] The ratio calculation formula of the hydraulic radius R, water flow cross-sectional area A, flow rate q and flow velocity v under different filling degrees to the water flow cross-sectional area A0, hydraulic radius R0, flow rate q0 and flow velocity v0 of full pipe flow can be derived as follows:

[0121]

[0122]

[0123]

[0124]

[0125] Where A0 is the cross-sectional area of ​​full flow (m2); R0 is the hydraulic radius of full flow (m);

[0126] q0 – full flow rate (m3 / s); v0 – full flow velocity (m / s).

[0127] The calculation results of the above formula are plotted as follows Figure 5 , which can be used for query and reference during manual calculation.

[0128] Depend on Figure 5 It can be seen that when the fullness When the pipe is full, the flow rate is the largest, which is 1.08 times the full pipe flow rate; when the fullness is When , the flow velocity in the tube is maximum, which is 1.14 times the flow velocity of full tube flow.

[0129] 3.3 Calculation of critical water depth

[0130] In a non-full circular pipe, given the flow rate q and pipe diameter D, the water depth and flow velocity at the pipe outlet are close to the critical water depth y and critical flow velocity v at that location.

[0131] Assume the Froude number of the water flow:

[0132] When Fr=1, y is the critical water depth, v=(gy)1 / 2 is the critical flow velocity, and g=9.81.

[0133] Fullness: or

[0134] Water flow cross-sectional area:

[0135] Flow rate by pipe section:

[0136]

[0137] When the pipe is full of flow, θ = 2∏, sinθ = 0, con(θ / 2) = -1, then q = 2.46D5 / 2.

[0138] Formula 3 can be rewritten as,

[0139]

[0140] It can be written as a nonlinear equation:

[0141]

[0142]

[0143] The first derivative of f(θ):

[0144]

[0145] The calculation formula for solving θ using Newton iteration method is as follows:

[0146]

[0147] Where k is the number of iterations and α is the iteration correction coefficient.

[0148] The calculation result of θ obtained from the above solution process is the angle between the center of the pipe and the two ends of the water surface line corresponding to the critical water depth, which can be directly used to calculate the critical water depth y, that is,

[0149]

[0150] Step 4: How to judge overflow and water accumulation

[0151] (1) Round tube

[0152] The drainage capacity of a circular pipe can be calculated by the following formula:

[0153]

[0154]

[0155] In the formula, Q0 is the drainage capacity of the circular pipe, A0 is the water flow cross-sectional area at full flow; v0 is the flow velocity at full flow, calculated using the Manning formula; R0 is the hydraulic radius at full flow; n is the pipe roughness coefficient; i is the pipe slope; and D is the pipe diameter.

[0156] When the sum of the upstream transfer flow and the flow in this section (set as Q) is greater than Q0, the drainage capacity of this pipe section is insufficient.

[0157] (2) Trapezoidal channel

[0158] Calculation of drainage capacity of trapezoidal channel:

[0159]

[0160] Where Q0 is the drainage capacity of the channel, b is the bottom width of the channel; h0 is the upper limit of the water depth at full flow; m is the channel slope coefficient (for a rectangular section, m = 0); n is the channel roughness coefficient; and i is the channel slope.

[0161] When the sum of the upstream transfer flow and the flow in this section (set as Q) is greater than Q0, the drainage capacity of the channel section is insufficient.

[0162] For an open channel, when the calculated channel depth h is greater than the upper limit of the channel depth h0, overflow will occur; for a closed channel, if (Q-Q0) in a certain period is greater than the water storage capacity of the inspection well, When the water accumulates and floods the streets, the overflow rate is

[0163] In the process of establishing the real-time dynamic hydraulic model of the drainage network, the platform software adopts a variable time difference correction algorithm. According to the changes in the flow and velocity status of the drainage network, the model calculation time step parameters are corrected in real time. This can ensure the real-time and timeliness of the simulation calculation of the drainage network operation status, improve the calculation accuracy of the hourly changes in the flow, velocity and fullness of the pipe section, and the correctness of the hydraulic state calculation.

[0164] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device.

[0165] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for early warning of urban drainage network, characterized by: The following steps are involved: a. Analyze the characteristics of regional rainfall and the current status of the drainage network system, and provide current status analysis and data support for establishing a drainage network model and formulating emergency response plans; b. Establish a drainage network model to provide a powerful tool for analyzing the operating conditions of the urban drainage network system and identifying system bottlenecks, while providing support for the optimization decision-making of urban drainage emergency response plans; c. Formulate an emergency plan for urban drainage to provide support for urban rescue and disaster relief when excessive rainfall occurs, thereby minimizing the losses caused by rainstorm disasters.

2. A method for calculating the load capacity of a town drainage network, characterized in that: The following steps are involved: Step 1: Establish a model of urban rainwater drainage network; Step 2: Design a water model; Step 3: Establish a mathematical model of the rainwater drainage network; Step 4: Determine overflow and water accumulation.

3. A method for calculating the load capacity of a town drainage network according to claim 2, characterized in that: The method for designing a water model includes the following steps: Step 21, drainage geometric expression method design, realized by pipe network diagram, the pipe network diagram is derived from the shape of pipe network layout; Step 22: Design of the pipe network association matrix, setting up a single drainage pipe network, defining the structural characteristics of the pipe network through data, and converting it into other types of pipe network model data; Step 23, model path matrix design, using the path numbers of all water flow pipe sections in the pipe network, to generate a set matrix including all water flow path pipe sections for the hydraulic mathematical model of the drainage pipe network.

4. The method for calculating the load capacity of a town drainage network according to claim 2, characterized in that: The method of establishing a mathematical model of a rainwater drainage network includes the following steps: Step 31, setting of rainfall process line, the simulated rainfall process adopted includes two types, one is to adopt synthetic rainfall process, the other is to adopt measured or historical rainfall process; Step 32, hydraulic calculation, the non-full flow in the circular pipe has a free surface, and relies on the gravity formed by the bottom slope of the pipe to flow from the high end to the low end, and determine the hydraulic relationship between the flow rate, flow velocity, cross-sectional size, fullness and slope of the pipe; Step 33: Calculate critical water depth.

5. A method for calculating the load capacity of a town drainage network according to claim 4, characterized in that: The method for setting the rainfall process line includes the following steps: The formula for rainstorm intensity is: The total rainfall during the period td is: Then the instantaneous rainfall intensity at time t is: This is an instantaneous rainfall process line with the same average rainfall intensity. The rain peak is formed at the proportion r of the duration after the rainfall starts. When the rainfall duration is: t=ta+tb, where tb is the duration of rainfall before the peak and ta is the duration of rainfall after the peak. Substituting formula 2 into formula 1, we have and In the calculation process, tb and ta are both time values ​​from the rain peak. The closer to the rain peak, the larger the i value.

6. A method for calculating the load capacity of a town drainage network according to claim 4, characterized in that: The method of hydraulic calculation includes the following steps: The Manning formula is introduced, which is applicable to hydraulic calculations of open channels, partially full pipe flows or rougher pipes. The formula is: In the formula, C is the Xie Cai coefficient; R is the hydraulic radius; n is the Manning roughness coefficient; Substituting the above formula into Xie Cai's formula, get: Where h f ―head loss along the way (m); v―average flow velocity of the water section (m / s); l-pipe length (m); Let i = hf / l, we can get: This formula is widely used in the hydraulic calculation formula for uniform flow in open channels and non-full pipe uniform flow; Substitute into the canal flow formula: q=A·v have to: In the formula, q is the flow rate of the pipe; A is the cross-sectional area of ​​the water flow (m2); I is the hydraulic gradient, which is the bottom slope of the pipe for uniform flow; The diameter of a circular pipe is D, the water depth in the pipe is y, and the filling degree is y / D. From geometry, we can derive the angle calculation formula from the center of the pipe to the two ends of the water surface line: Where θ is in radians; or Water flow cross-sectional area: Wet week: Hydraulic radius: Assume that the cross-sectional area, hydraulic radius, flow rate and flow velocity of full pipe flow are A0, R0, q0 and v0 respectively. Then A0=πD 2 / 4 and R0=D / 4, and The ratio calculation formula of the hydraulic radius R, water flow cross-sectional area A, flow rate q and flow velocity v under different filling degrees to the water flow cross-sectional area A0, hydraulic radius R0, flow rate q0 and flow velocity v0 of full pipe flow can be derived as follows: Where, A0 is the cross-sectional area of ​​full flow (m2); R0 is the hydraulic radius of full flow (m); q0 – full flow rate (m3 / s); v0 – full flow velocity (m / s).

7. A method for calculating the load capacity of a town drainage network according to claim 4, characterized in that: The method for calculating critical water depth includes the following steps: In a non-full circular pipe, given the flow rate q and pipe diameter D, the water depth and flow velocity at the pipe outlet are close to the critical water depth y and critical flow velocity v at that location; Assume the Froude number of the water flow: When Fr = 1, y is the critical water depth, v = (gy)1 / 2 is the critical flow velocity, and g = 9.81; Fullness: or Water flow cross-sectional area: Flow rate by pipe section: When the pipe is full of flow, θ = 2∏, sinθ = 0, con(θ / 2) = -1, then q = 2.46D5 / 2 Formula 3 can be rewritten as, It can be written as a nonlinear equation: The first derivative of f(θ): The calculation formula for solving θ using Newton iteration method is as follows: In the formula, k is the number of iterations, and α is the iteration correction coefficient; The calculation result of θ obtained from the above solution process is the angle between the center of the pipe and the two ends of the water surface line corresponding to the critical water depth, which can be directly used to calculate the critical water depth y, that is, 8. A method for calculating the load capacity of a town drainage network according to claim 2, characterized in that: The method for calculating critical water depth includes the following steps: The drainage capacity of a circular pipe can be calculated by the following formula: In the formula, Q0 is the drainage capacity of the circular pipe, A0 is the water flow cross-sectional area at full flow; v0 is the flow velocity at full flow, calculated using the Manning formula; R0 is the hydraulic radius at full flow; n is the pipe roughness coefficient; i is the pipe slope; D is the pipe diameter; When the sum of the upstream transfer flow and the flow of this section (set as Q) is greater than Q0, the drainage capacity of this pipe section is insufficient; Calculation of drainage capacity of trapezoidal channel: Where Q0 is the drainage capacity of the channel, b is the bottom width of the channel; h0 is the upper limit of the water depth at full flow; m is the channel slope coefficient (for a rectangular section, m = 0); n is the channel roughness coefficient; i is the channel slope; When the sum of the upstream transfer flow and the flow of this section (set as Q) is greater than Q0, the drainage capacity of this channel section is insufficient; For an open channel, when the calculated channel depth h is greater than the upper limit of the channel depth h0, overflow will occur; for a closed channel, if (Q-Q0) in a certain period is greater than the water storage capacity of the inspection well, When the water accumulates and floods the streets, the overflow rate is

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