A method for preventing flash floods based on flow control

Abstract

This invention provides a method for preventing flash floods based on flow control, including determining the maximum allowable flow rate of a river section, the maximum allowable discharge flow rate of each tributary, the design flow process of the tributaries, and the method for regulating water volume. Based on the above information, it also presents the design concept for the orifice size of the control dam used in this measure. Compared with the current common method of simply raising the levee standards of urban river sections to resist flash floods, this method only changes the flow process when the flood flow exceeds the design standard, without changing the flow process of the tributaries at other times, thus avoiding long-term inundation; it only requires the construction of the dam body, without the need for gates or other control facilities, resulting in low investment; it eliminates operational scheduling issues, effectively reducing urban flash flood losses and achieving high overall benefits; after the flood, only possible debris such as branches need to be cleared to prevent orifice blockage, resulting in low maintenance costs. This method is beneficial for the development of flash flood prevention work in mountainous towns, enabling more effective resistance to flash floods and prevention of urban flooding.

Description

Technical Field

[0001] This invention relates to the field of flash flood prevention, specifically a flash flood prevention method based on flow control. Background Technology

[0002] Mountain torrents have always been one of the most challenging natural disasters to control in my country. In my country's mountainous areas, many towns are located at the confluence of multiple tributaries. Under heavy rainfall conditions, mountain floods converge rapidly, easily leading to the inundation of towns. Traditional methods of mountain torrent control, which simply rely on raising the standards of river levees in urban areas to resist mountain torrents, are not only ineffective but may also cause drainage difficulties and urban flooding due to excessively high levees, resulting in additional losses.

[0003] In conclusion, for the safety of people's lives and property, and considering the difficulty of construction in mountainous areas, a flood prevention measure that is easy to implement, low in cost, high in efficiency, and has minimal impact on the ecological environment is extremely necessary and has broad application prospects. Summary of the Invention

[0004] The purpose of this invention is to address the problem that in mountainous towns located at the confluence of multiple tributaries, under heavy rainfall conditions, mountain floods converge rapidly. Simply raising the standards of the river embankments in these towns to resist flash floods is not only ineffective but may also lead to drainage difficulties and urban flooding due to excessively high embankments. This invention provides a flash flood prevention method based on flow process control. By constructing flow control dams on tributaries, the maximum inflow of tributaries is strictly controlled, thereby regulating the flood process of the tributaries to prevent flash floods.

[0005] The present invention solves the above-mentioned technical problems by adopting the following technical solution:

[0006] A flash flood prevention method based on flow process control includes the following steps:

[0007] a. By using historical rainfall data and hydrological data of urban river sections, determine the urban flash flood defense standards and obtain the maximum allowable flow rate for the river section;

[0008] b. Based on the proportion of the tributary catchment area, allocate the peak flow control target of each tributary and the maximum allowable flow of the river section obtained in step a, and determine the maximum allowable discharge flow of each tributary;

[0009] c. The process of calculating the design flow of tributaries based on historical rainfall data;

[0010] d. Based on the design flow process of each tributary calculated in step c and the maximum allowable discharge flow obtained in step b, determine whether regulation is required and the amount of water to be regulated. If the design flow process of each tributary calculated in step c exceeds the maximum allowable discharge flow obtained in step b, then regulation is implemented and the amount of water to be regulated is calculated; otherwise, no regulation is required.

[0011] e. Based on the water volume that needs to be regulated obtained in step d, determine the required reservoir capacity. Then, comprehensively determine the dam site and dam height based on topography, geological conditions, transportation, and temporary land inundation area to meet the reservoir capacity requirements. Determine the size of the spillway openings based on the maximum allowable discharge flow of each tributary.

[0012] Furthermore, in step b, the maximum allowable discharge flow Q of each tributary is determined. i The calculation formula is as follows:

[0013]

[0014] In the formula Q M The maximum flow rate allowed through the river section; F i F represents the catchment area of ​​the tributary basin; F represents the total catchment area of ​​the basin.

[0015] Furthermore, in step c, the unit hydrograph method is used to calculate the design flow of the tributary based on historical rainfall data. The specific calculation formula is as follows:

[0016]

[0017]

[0018] r i The surface net rainfall process is given by the rainfall data; R i To correspond to surface runoff processes; unit hydrograph time interval Δt is in hours; watershed area F is in km². 2 The calculation is as follows: where i is a natural number greater than or equal to 4 and less than or equal to n, and the value of n ranges from 8 to 24. The specific value is determined based on the value of Δt for the unit linear period and the time span covered by historical rainfall data.

[0019] Furthermore, in step e, the method for calculating the size of the spillway orifice should refer to the design calculation method for the outflow of a broad-crested weir dam. Given a predetermined orifice height h, the formula for calculating the orifice width b is as follows:

[0020]

[0021] Where Q is the design flow rate, which is the maximum allowable discharge flow rate of each tributary; H0 is the weir head including the approach velocity head; g is the gravitational acceleration; σ and μ are the submergence coefficient and flow coefficient of the orifice flow over the broad crest weir, respectively.

[0022] Compared with the prior art, the present invention has the following advantages:

[0023] (1) Effectively reduce urban flash flood losses by only changing the flow process when the flood flow exceeds the design standard, without changing the flow process of the tributary at other times, and will not cause long-term flooding;

[0024] (2) Only the dam body needs to be built, without the need for control facilities such as gates, resulting in a small investment;

[0025] (3) It is simple to use, there are no operational scheduling problems, and the overall benefits are high;

[0026] (4) After the flood, only the possible branches and other debris need to be removed to prevent the opening from being blocked, and the maintenance cost is low. Attached Figure Description

[0027] Figure 1 This is a schematic flowchart of a flash flood prevention method based on flow control according to the present invention;

[0028] Figure 2 This is a simplified schematic diagram of the flow control dam used in this invention;

[0029] Figure 3 This is a line graph showing the design flow rate before and after the regulation of tributary A in this embodiment of the invention.

[0030] Figure 4 This is a line graph showing the design flow rate process before and after regulation of tributary B in an embodiment of the present invention. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] like Figure 1 As shown, the standards for urban flash flood defense, the required water volume for each tributary, and the orifice size of the control dam are determined by the following steps:

[0033] a. By using historical rainfall data and hydrological data of urban river sections, determine the urban flash flood defense standards and obtain the maximum allowable flow rate for the river section;

[0034] b. Based on the proportion of the tributary catchment area, allocate the peak flow control target for each tributary, that is, determine the maximum allowable discharge flow of each tributary;

[0035] c. The process of calculating the design flow of tributaries based on historical rainfall data;

[0036] d. Determine whether regulation is needed and the amount of water requiring regulation based on the design flow process and maximum allowable discharge flow of each tributary;

[0037] e. The dam site and dam height are determined comprehensively based on factors such as the amount of water to be regulated, topography, geological conditions, transportation, and the area of ​​land temporarily submerged to meet the reservoir capacity required for water regulation. The size of the spillway is determined based on the maximum allowable discharge flow of each tributary.

[0038] like Figure 2 The diagram illustrates a simplified flow control dam as described in this invention. This process determines the dam site, dam height, and orifice dimensions. Only the dam body is constructed; control facilities such as gates are omitted. This method strictly controls the maximum inflow of the tributary. When the inflow exceeds the tributary's maximum allowable flow, the excess water is temporarily stored upstream of the dam. Only water not exceeding the tributary's maximum allowable discharge is released downstream, effectively ensuring the safety of the town.

[0039] Example:

[0040] A town has two tributaries, A and B, upstream of it, with catchment areas of 339 km² and 339 km² respectively. 2 and 226km 2 The measured cross-sectional areas are respectively known to be 260m². 3 Table 1 shows the surface net rainfall data for the two tributaries during a historical maximum rainfall event. The design flood for this river section can be estimated using this rainfall data.

[0041] Table 1. Surface net rainfall data within the watersheds of tributaries A and B.

[0042]

[0043] The specific implementation of the flash flood prevention measures in this invention is as follows:

[0044] a. By using historical rainfall data and hydrological data of urban river sections, determine the urban flash flood defense standards and obtain the maximum allowable flow rate for the river section;

[0045] The data indicates that the flood defense standard for this town is 260m. 3 / s, meaning the maximum allowable flow rate for that river segment is Q. M =260m 3 / s.

[0046] b. Based on the proportion of the tributary catchment area, allocate the peak flow control target for each tributary, that is, determine the maximum allowable discharge flow of each tributary;

[0047] The results are obtained from the catchment areas of the two tributaries, A and B.

[0048] The maximum permissible discharge flow in basin A is Q1 = Q M ×339 / 565=156m 3 / s,

[0049] The maximum permissible discharge flow in Basin B is Q2 = Q M ×226 / 565=104m 3 / s.

[0050] c. The process of calculating the design flow of tributaries based on historical rainfall data;

[0051] The design flow process lines for branches A and B, calculated using the unit hydrograph method, are shown in Table 2.

[0052] Table 2 Design flow process lines for branches A and B

[0053] t (time) 6 7 8 9 10 11 12 13 14 15 <![CDATA[Q A (m 3 / s)]]> 0 17.4 77.2 168.8 195.8 157.0 81.6 39.4 13.6 0 <![CDATA[Q B (m 3 / s)]]> 0 12.8 51.4 103.4 134.0 105.6 54.6 15.6 8.8 0

[0054] d. Determine whether regulation is needed and the amount of water requiring regulation based on the design flow process and maximum allowable discharge flow of each tributary;

[0055] Based on comparison, it was determined that the designed flow rates of both tributaries exceeded the maximum allowable discharge flow rates during the three time periods of 9, 10, and 11, necessitating water volume regulation.

[0056] e. The dam site and dam height are determined comprehensively based on factors such as the amount of water to be regulated, topography, geological conditions, transportation, and the area of ​​land temporarily submerged to meet the reservoir capacity required for water regulation. The size of the spillway is determined based on the maximum allowable discharge flow.

[0057] Based on the design flow process curves of branches A and B, the maximum water volume requiring regulation is approximately 409,000 m³ / s. 3 and 312,000 m 3 Assuming the highest water levels corresponding to the maximum required water volume are 45m and 30m respectively, derived from the water level and reservoir capacity curves of tributaries A and B, the flow coefficient μ = 0.37 and the inundation coefficient σ = 0.76 for tributary A; and the flow coefficient μ = 0.41 and the inundation coefficient σ = 0.82 for tributary B, the orifice size of the flow control dam for tributary A can be calculated using equation (4) to be 4m × 5.6m. Similarly, the orifice size of the flow control dam for tributary B can be 3.5m × 4.5m.

[0058] Based on flood control calculations, the design flow process lines for tributaries A and B after regulation are shown in Table 3:

[0059] Table 3. Design flow process lines of branches A and B after regulation and storage.

[0060] t (time) 6 7 8 9 10 11 12 13 14 15 <![CDATA[Q A (m 3 / s)]]> 0 17.4 57.0 97.2 139 156.0 129.8 85.6 50.8 18.0 <![CDATA[Q B (m 3 / s)]]> 0 12.8 37.4 63.8 90.6 104.0 86.6 55.6 25.0 11.0

[0061] The design flow curves of branches A and B before and after water storage are as follows: Figure 3 , 4 As shown, the flow rate was strictly controlled when it exceeded the maximum allowable discharge flow of the tributary. The water temporarily stored by the control dam was gradually discharged downstream after the flood peak. During the rainstorm, the discharge flow of the river section never exceeded the urban flash flood defense standard, and the safety of the town was effectively guaranteed.

[0062] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A flash flood control method based on flow process control, characterized in that, The method comprises the following steps: a. determining a town flood prevention standard through historical rainfall data and town river section hydrological data to obtain a maximum allowable discharge of the river section; b. Based on the proportion of the catchment area of the tributary, the peak flow control target of each tributary and the maximum allowable flow of the river section obtained in step a are allocated to determine the maximum allowable discharge of each tributary; the maximum allowable discharge of each tributary is determined in step b Q i The calculation formula is as follows: where Q M is the maximum flow allowed to pass through the reach; F i is the tributary watershed catchment area; F is the total watershed catchment area; c. calculating a branch stream design discharge process according to the historical rainfall data; d. determining whether regulation is needed and the water quantity needing regulation according to the maximum allowable discharge obtained in step b and the branch stream design discharge process obtained in step c, if there is a case of exceeding the maximum allowable discharge in the branch stream design discharge process obtained in step c, the water quantity needing regulation is calculated, otherwise, regulation is not needed; e. determining the required reservoir capacity according to the water quantity needing regulation obtained in step d, and then determining a dam site and a dam height according to topography, geological conditions, traffic and temporary land inundation area to meet the reservoir capacity requirement, and determining a discharge hole size according to the maximum allowable discharge of the branch stream, wherein the dam is a flow control dam, only a dam body is built without a control facility including a gate, and in the case of exceeding the maximum allowable discharge of the branch stream, the excess water is temporarily stored in the upstream of the flow control dam, and only the water flow not exceeding the maximum allowable discharge of the branch stream is discharged to the downstream; In step c, the unit line method is used to calculate the branch stream design discharge process according to the historical rainfall data, and the specific calculation formula is as follows: r i is a known net rainfall process on the ground; R i is a corresponding ground runoff process; the unit line time period△t is in hours; the watershed area F is in km 2 ; wherein i is a natural number greater than or equal to 4 and less than or equal to n, the value range of n is 8 to 24, and the specific value is determined according to the value of the unit line time period△t and the time span covered by the historical rainfall data. In step e, the method for calculating the discharge hole size should refer to the design calculation method of the outflow of the wide-top weir gate dam hole, and under the premise of having determined the hole height h, the calculation formula of the hole width b is as follows: wherein Q is the design discharge, which is the maximum allowable discharge of the branch stream; H0 is the weir water head considering the velocity head; g is the gravity acceleration; and σ and μ are respectively the submergence coefficient and the discharge coefficient of the wide-top weir hole flow.

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