A flash flood prevention method based on the combination of dams, pipes and beaches

Abstract

The present invention belongs to the technical field of water conservancy engineering, and relates to a flash flood prevention and control method based on the combination of dams, pipes and flood beaches. The possibility of extremely large flash floods is predicted according to the influence of underlying surface characteristics on precipitation. According to target requirements, at least one flash flood prevention and control system connected in series with the river is selected on a site to be constructed on the river. During the flood season, flash flood prevention and control is carried out through the flash flood prevention and control system. If it is not an extremely large flash flood, the flood is diverted through drainage pipes, and the flood is reduced by a flood-removing dry riverbed or a flood-removing beach, without leaving surface runoff. If it is an extremely large flash flood, the flood in the flood-blocking reservoir is allowed to overflow over the dam, and the drainage pipe diversion and extremely large overflow are allowed to enter the flood-removing dry riverbed or the flood-removing beach to dissipate energy and discharge flood. After the flood, the flash flood prevention and control system is repaired. The present invention intercepts and stores flood water by a dam, diverts and removes flood water through pipelines and a dry riverbed, and then enters the downstream river channel, so that the risk of flash flood disasters is greatly reduced, so as to meet the basic standards for flash flood prevention and control.

Description

Technical Field

[0001] The invention belongs to the technical field of water conservancy projects, and in particular relates to a method for preventing and controlling mountain torrents based on the combination of dams, pipes and beaches. Background Art

[0002] At present, the available methods for preventing and controlling flash floods are mainly divided into two categories, engineering measures and non-engineering measures. The present invention belongs to engineering measures. Among them, non-engineering measures include early warning methods or risk assessment methods for flash floods, such as analyzing and modeling climate, rainfall, underlying surface conditions, etc., analyzing the probability of flash floods, calculating and setting the size of the early warning flow, specifying the site selection of the dam and the maximum discharge flow allowed when the corresponding early warning flow is reached.

[0003] Engineering measures mainly include the design, construction and invention of retaining dams and drainage channels. Among them, the purpose of retaining dams is to initially retain large rocks in mountain torrents and weaken the flood peak, but its interception effect is limited and it is easy to silt up or break the dam. In the present invention, it is combined with a small reservoir upstream to improve the prevention and control effect. Most of the existing drainage channel inventions can collect rainwater and divert it away without contacting the mountain soil layer, but the pipeline drainage flow is limited. On the one hand, the prevention and control effect is limited, and on the other hand, the pipelines are connected in series, and local obstacles are easy to cause overall imbalance and low stability.

[0004] From the above, it can be seen that the existing patents for engineering projects for preventing and controlling mountain torrents generally have the problems of general prevention and control effects, poor stability, and lack of systematicity. The present invention is proposed to address the above problems. Summary of the invention

[0005] The purpose of the present invention is to overcome the deficiencies in the prior art and provide a method for preventing and controlling mountain torrents based on the combination of dams, pipes and beaches.

[0006] In order to achieve the purpose of the present invention, we will adopt the following technical solution to implement it:

[0007] A flash flood prevention method based on a combination of dams, pipes and beaches comprises the following steps:

[0008] S1. Analyze the influence of the underlying surface characteristics on precipitation according to the river section of the flash flood control planning and design, and predict the possibility of the occurrence of major flash floods in the flash flood control area in the future;

[0009] S2. According to the objectives and requirements of flash flood prevention and control work, combined with the underlying surface characteristics and the possibility of a major flood as described in step S1 and the characteristics of the flash flood runoff in the flash flood prevention and control planning and design river section, at least one flash flood prevention and control system connected in series on the river is selected and constructed in the flash flood prevention and control planning and design river section. The flash flood prevention and control system includes a flood control dam built on the river course, a flood control reservoir built upstream of the flood control dam, and a flood control dry riverbed or flood control dry river beach built downstream of the flood control dam, and a drainage pipe buried in the flood control dry riverbed or flood control dry river beach. The water inlet of the drainage pipe is arranged at the bottom of the flood control reservoir, and the water outlet is arranged in the river course downstream of the flood control dry riverbed or flood control dry river beach.

[0010] S3: During the flood season, floods are blocked by flood control dams and stored in dry flood control reservoirs;

[0011] S4. Determine whether the mountain torrent is a particularly large mountain torrent based on meteorological data. If not, divert the flood through the drainage pipes and reduce the flood through the flood control dry riverbed or flood control dry river beach, leaving no surface runoff. If so, allow the flood in the flood control reservoir to overflow the dam, divert the flood through the drainage pipes, and allow the particularly large overflow to enter the flood control dry riverbed or flood control dry river beach to dissipate energy and discharge the flood. If the overflow causes the flood control dam to fail, the flood control dam must be repaired in a timely manner.

[0012] S5. After the flood, the flash flood control system is repaired.

[0013] As an additional solution of the present invention, a flood retention and slag blocking forest net and a cross-linked rope net are additionally provided on the flood control dry riverbed or flood control dry river beach.

[0014] As an alternative to the present invention, when there are key flood control facilities downstream of the river in the flash flood control area, at least two flash flood control systems connected in series are built upstream of the river to reduce the flood peak and the destructive power of the flash flood.

[0015] As an alternative to the present invention, when the mountain torrent is a particularly large mountain torrent, at least two mountain torrent prevention and control systems connected in series can be constructed to reduce the flood peak and the destructive power of the mountain torrent.

[0016] As a preferred solution of the present invention, when at least two of the mountain torrent control systems are connected in series, the length and height of the flood control dam backfill area need to be considered:

[0017]

[0018] Hn=ζ n-1 εD 80

[0019] Where, L s,n is the length of the silting area in front of the nth flood control dam, in meters, H nis the height of the nth flood control dam, in meters, S init,n is the original ditch bed gradient at the site of the nth flood control dam, expressed as %, determined according to the on-site investigation, ξ is the calculation coefficient, ranging from 0.5 to 0.9, ζ is the calculation coefficient, ranging from 0.6 to 0.8, ε is the calculation coefficient, ranging from 5 to 8, D 80 It is the characteristic particle size of the ditch bed in front of the first flood control dam, in m, determined by on-site investigation.

[0020] As a preferred solution of the present invention, the flood control dam adopts a low, wide and large dam body, the back water slope is longer and gentler than the front water slope, and it can leak water and overflow the dam.

[0021] As a preferred embodiment of the present invention, the diameter of the drainage pipe is determined according to the multi-year average flow rate of the flood control dry riverbed or the flood control dry river beach during the flood season and the pipeline flow rate; the pipe diameter calculation formula is as follows:

[0022]

[0023] Where Q is the flow rate in m 3 / h or t / h; D is the inner diameter of the pipe, in meters; V is the average velocity of the fluid, in meters per second.

[0024] As a preferred embodiment of the present invention, the flood retention and slag blocking forest network includes an artificial column group and a tree and shrub forest, wherein the tree and shrub forest is specifically a tree and grass belt, and the average breast diameter of the trees in the tree and grass belt is Dtree> the critical diameter of the tree damage D max .

[0025] As a preferred embodiment of the present invention, the critical diameter D of the tree is max It is determined by the following calculation:

[0026]

[0027] Where D max is the critical diameter of tree failure, in m; σ is the compressive strength of tree wood along the grain, in kN / m 2 , determined by the tree species; D is the diameter of large debris flow blocks, in meters; h df The depth of debris flow at the site of the flood control dam; F 大块石 、F 泥石流 They are respectively the impact force of large rocks in debris flow and the impact force of debris flow, the unit is kN, and they are determined by on-site investigation.

[0028] As a preferred embodiment of the present invention, the flood control dry riverbed or flood control dry river beach is selected from a river section or beach covered with a thick gravel layer, and the longer the better.

[0029] Beneficial Effects

[0030] The present invention reduces the flow rate and flood peak through a small reservoir + dry riverbed + pipeline system, thereby achieving the purpose of preventing and controlling mountain torrents. The mountain torrent peak passes through three small reservoirs + dry riverbed + pipeline system, and then enters the downstream river channel. The flood peak is greatly flattened, and the risk of mountain torrent disasters is greatly reduced.

[0031] The first method of flood control is to store flood water by means of flood control dams, and to retain flood water in upstream reservoirs when the reservoirs are dry, thereby reducing the flow rate of mountain torrents and reducing their destructive power.

[0032] The second is flood control by pipeline diversion. The role of the pipeline network is to drain water through pipelines, so that the pipeline flow does not participate in the formation of open flow in the river, and the pipeline flow does not participate in the process of shaping the flood peak, decomposing the flood peak runoff, so that the first pipeline runoff is separated from the flood, directly reducing the flood peak water volume, and the second pipeline water flow is separated from the river flood, does not participate in the construction of the flood peak superposition, does not give the flood greater kinetic energy, and scours the riverbed. The mountain torrents and rainwater diverted by the pipeline no longer come into contact with the soil and rocks below, and prevents excessive mountain torrents and rainwater from further scouring the soil and rocks below the valley. After the mountain torrents and rainwater overflowing from the upstream dam area are diverted, the amount of water flowing from the upstream dam area to the downstream dam area is greatly reduced, and the rainwater on the top of the mountain will not converge to the foot of the mountain, avoiding a large amount of mountain torrents and rainwater from gathering at the bottom of the mountain, making the bottom saturated with water, and reducing the risk of causing mudslides.

[0033] The third flood control is the flood control of the dry riverbed. When mountain torrents overflow the dams of small reservoirs, the overflowing flood water enters the dry riverbed section while ensuring that the dams can overflow but not break. The gaps in the gravel of the dry riverbed first absorb water to control the flood, playing the role of the first wave of strangling the development of the flood peak. Then the grass and shrub forests and professional flood control forests on the dry riverbed have the function of significantly slowing down the advancement speed of the flood peak and intercepting floating objects in the flood. Its most important role is to retain flood water and temporarily stagnate the river section. Finally, the high water level increases the width of the river to control the flood.

[0034] Dry riverbeds are more effective in preventing floods than flowing riverbeds, especially dry riverbeds filled with sand and gravel. When a flood peak comes, it first absorbs a large amount of water to fill the gaps, and then increases the roughness of the riverbed to slow down the flood. Unlike rivers with abundant runoff, dry riverbeds at least do not contribute to the flood peak.

[0035] It can be seen from this that generally, after the peak of a mountain torrent passes through three small reservoirs + dry riverbed + pipeline system for flood control, the peak that enters the downstream river channel will be greatly flattened, the risk of mountain torrent disasters will be greatly reduced, and ordinary river sections can basically meet the basic standards for preventing and controlling mountain torrents. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a schematic diagram of the cross-sectional structure layout of the mountain torrent prevention and control system of the present invention;

[0037] Figure 2It is a schematic diagram of the planar structural layout of the mountain torrent prevention and control system of the present invention;

[0038] Figure 3 It is a flow chart of the non-flood season system operation of the flash flood control system of the present invention;

[0039] Figure 4 This is a flow chart of the flood season system operation of the mountain torrent control system of the present invention. DETAILED DESCRIPTION

[0040] The present invention will be further described based on the accompanying drawings and embodiments.

[0041] As an embodiment of the present invention, Figure 1 and 2 As shown, a flash flood prevention method based on a combination of dams, pipes and beaches, the flash flood prevention method includes the following steps:

[0042] S1. Analyze the influence of the underlying surface characteristics on precipitation according to the river section of the flash flood control planning and design, and predict the possibility of the occurrence of major flash floods in the flash flood control area in the future;

[0043] S2. According to the objectives and requirements of flash flood prevention and control work, combined with the underlying surface characteristics and the possibility of a major flood as described in step S1 and the characteristics of the flash flood runoff in the flash flood prevention and control planning and design river section, at least one flash flood prevention and control system connected in series on the river is selected and constructed in the flash flood prevention and control planning and design river section. The flash flood prevention and control system includes a flood control dam built on the river course, a flood control reservoir built upstream of the flood control dam, and a flood control dry riverbed or flood control dry river beach built downstream of the flood control dam, and a drainage pipe buried in the flood control dry riverbed or flood control dry river beach. The water inlet of the drainage pipe is arranged at the bottom of the flood control reservoir, and the water outlet is arranged in the river course downstream of the flood control dry riverbed or flood control dry river beach.

[0044] S3: During the flood season, floods are blocked by flood control dams and stored in dry flood control reservoirs;

[0045] S4. Determine whether the mountain torrent is a particularly large mountain torrent based on meteorological data. If not, divert the flood through the drainage pipes and reduce the flood through the flood control dry riverbed or flood control dry river beach, leaving no surface runoff. If so, allow the flood in the flood control reservoir to overflow the dam, divert the flood through the drainage pipes, and allow the particularly large overflow to enter the flood control dry riverbed or flood control dry river beach to dissipate energy and discharge the flood. If the overflow causes the flood control dam to fail, the flood control dam must be repaired in a timely manner.

[0046] S5. After the flood, the flash flood control system is repaired.

[0047] The mountain torrent control system is deployed in the river section designed for mountain torrent control, and achieves the purpose of mountain torrent control by reducing flood peaks and lowering flow rates.

[0048] (1) Upstream flood control dams and flood control reservoirs

[0049] The dam body should be low, wide and large, with the back slope longer and gentler than the front slope. The dam surface should be paved with large-diameter stone gravel or stone cages. Ensure that it will not be washed back during the flood. The dam body can leak and overflow, but it cannot collapse during the flood.

[0050] The required storage capacity is determined based on the amount of water that needs to be regulated according to the design flow, and the dam site and dam height are determined comprehensively based on the topography, geological conditions, transportation, and temporary land inundation area to meet the storage capacity requirements. The size of the spillway is determined based on the maximum allowable discharge flow of each tributary. The method for calculating the size of the spillway should refer to the design calculation method for the outflow of the orifice of the wide crested weir dam. Under the premise that the orifice height h has been determined, the calculation formula for the orifice width b is as follows:

[0051]

[0052] Where Q is the design flow, which is the maximum allowable discharge flow of each tributary; H0 is the head above the weir taking into account the head of the approaching flow velocity; g is the gravitational acceleration; σ and μ are the flooding coefficient and discharge coefficient of the hole flow on the wide crest weir, respectively.

[0053] (2) Drainage pipes

[0054] In the design of flood control river sections, a water pipeline system is laid along the river. The pipeline inlet is at the bottom of the upstream small reservoir, and the outlet is in the river channel downstream of the flood control river beach. The pipeline can be buried in the riverbed or beach to ensure that it will not be washed away during floods. The function of the drainage pipeline is to guide the flood base flow to be discharged from the pipeline, not to go to the downstream river beach and open channel.

[0055] The pipe diameter is determined based on the multi-year average flow rate and pipeline velocity during the flood season of the river section. The pipe diameter calculation formula is as follows:

[0056]

[0057] Where Q is the flow rate in m 3 / h or t / h; D is the inner diameter of the pipe, in meters; V is the average velocity of the fluid, in meters per second.

[0058] The length of the pipeline is determined according to the planned and designed length of the flood control dry river beach, which is longer than the flood control dry river beach.

[0059] Taking the commonly used long pipe free outflow as an example, the head loss calculation formula is:

[0060]

[0061] Where H is the head, which can be converted from pressure, L is the length of the pipe, v is the flow velocity of the pipe outflow, R is the hydraulic radius, and C is the Schertz coefficient.

[0062] (3) Flood control dry riverbed or flood control dry river beach

[0063] The flood-relief dry riverbed or flood-relief dry river beach is an artificially created section of the flood-relief dry riverbed or flood-relief dry river beach, which is equivalent to a super energy dissipation pool for mountain torrents.

[0064] The best location for the flood control dry riverbed or flood control dry river beach is the river section with a thick gravel layer on the riverbed, such as the river section where debris flow remains are deposited. Generally speaking, the longer the flood control dry riverbed or flood control dry river beach, the better. It is best to be several kilometers, at least hundreds of meters. Where conditions permit, a flood retention and slag forest network (a group of artificial pillars and trees and shrubs) plus a cross-linked rope network can be added to the dry river beach.

[0065] The present invention further provides the selection conditions of trees in ecological engineering measures, specifically, the tree-grass belt, the average breast diameter of the tree Dtree> the critical diameter of the tree damage Dtree max This condition can ensure that the maximum bending moment M that trees in the tree-grass belt can withstand can resist the impact of mountain torrents and mud-rock flows. max Calculate according to the following formula:

[0066]

[0067] Where D max is the critical diameter of tree failure, in m; σ is the compressive strength of tree wood along the grain, in kN / m 2 , determined by the tree species; D is the diameter of large debris flow blocks, in meters; h df The depth of debris flow at the site of the flood control dam; F 大块石 、F 泥石流 are the impact force of large rocks in debris flow and the impact force of debris flow, respectively, in kN, determined by on-site investigation;

[0068] Flood control dams and upstream flood control reservoirs are built after selecting a site based on the characteristics of the underlying surface of the target area for mountain torrent prevention and control. Then the pipeline is buried in the riverbed or beach. The pipeline inlet is at the bottom of the upstream flood control reservoir, and the outlet is in the river channel downstream of the flood control dry riverbed or the flood control dry river beach. A flood retention and slag forest network (an artificial group of columns and tree and shrub forests) plus a cross-connected rope network can be added to the flood control dry riverbed or the flood control dry river beach.

[0069] In particular, for the prevention of super flash floods, and the presence of key flood control facilities in the downstream of the river, such as concentrated settlements in towns and villages, factories and mines, traffic arterial bridges and other key protection objects, more than two flash flood control systems can be arranged in series in the upstream river section of the key protection objects, referred to as the river channel duplex flash flood control system. After the multi-level flood peak reduction process of the duplex flash flood control system, the destructive capacity of flash floods is greatly reduced. When multiple systems are connected in series, the length and height of the flood dam backfill area must be considered:

[0070]

[0071] Hn=ζ n-1 εD 80 ,

[0072] Where, L s,n is the length of the silting area in front of the nth flood control dam, in meters, H n is the height of the nth flood control dam, in meters, S init,n is the original ditch bed gradient at the site of the nth flood control dam, expressed as %, determined according to the on-site investigation, ξ is the calculation coefficient, ranging from 0.5 to 0.9, ζ is the calculation coefficient, ranging from 0.6 to 0.8, ε is the calculation coefficient, ranging from 5 to 8, D 80 It is the characteristic particle size of the ditch bed in front of the first flood control dam, in m, determined by on-site investigation.

[0073] In particular, in areas with severe soil erosion and where silt dam systems have been built, in order to develop flash flood control systems according to local conditions, the silt dam systems are transformed for flash flood control. On the basis of the silt dam system, the most important thing is to add a set of drainage pipe systems to form a dry reservoir plus dry river beach flash flood control system, which has a similar effect to the "dam + pipe + beach combination". The key is that small flood-blocking dams can prevent the dams from breaking during the strong flood peak. In a multi-stage silt dam system, even if a small silt dam breaks, at least the main silt dam will not break. All of these can greatly reduce flash flood disasters.

[0074] The operation of the present invention can be divided into flood season and non-flood season operation, wherein the non-flood season mainly involves system maintenance, and the flood season is an important period for the system to function.

[0075] (1) Operation during non-flood season

[0076] The non-flood season generally refers to the period from November each year to May of the following year, when rainfall is scarce and generally no large flood peaks can form. During the non-flood season, the "upstream small reservoir (silt dam, barrier lake) + pipeline network + dry riverbed" system is mainly used for water storage and irrigation. Small reservoirs can appropriately intercept and store water. The intercepted water can be used for local irrigation and water supply along the river. The non-flood season is also the construction and maintenance period of the "upstream small reservoir (silt dam, barrier lake) + pipeline network + dry riverbed" system to ensure that the system's flood prevention and disaster reduction design goals are achieved during the flood season. It mainly involves dam body maintenance, construction and maintenance of artificial flood control forests on dry river channels, and pipeline system maintenance. Non-flood season operations are as follows: Figure 3 shown.

[0077] (2) Operation during flood season

[0078] The flood season generally refers to the period from June to October each year. During the flood season, there is abundant rainfall, the soil is saturated, and rainstorms and flash floods occur frequently. During the flood season, the small reservoirs and flood control dams upstream work together to intercept sand and gravel and reduce the flow rate of floods, becoming the first line of defense for flood interception; then the flood flows out from the spillway into the pipeline, dispersing the flood flow and reducing the flood peak, which is the second line of defense for flood interception; finally, the dry riverbed absorbs water to dissipate the flood. When a large flood overflows the dam, it can flow into the dry riverbed and enter the flood dissipation. Through flood detention and temporary water congestion in the river section, it slows down the advancement of the flood peak and intercepts floating objects in the flood, which is the third line of defense for flood interception. During the operation of the flash flood control system during the flood season, such as Figure 4 shown.

[0079] The "upstream small reservoir (silt dam, barrier lake) + pipe network + dry riverbed" system is mainly used for mountain torrent prevention and control. The following points should be noted during operation:

[0080] Before the flood comes, it is necessary to empty the small reservoirs upstream in advance to ensure that they are below the dead storage capacity. It is best to keep the reservoir dry as much as possible to prepare for the attack of mountain torrents at any time. Cooperate with the flood control dam to intercept sand and gravel and reduce the flow rate of floods. For the runoff entering the reservoir, first ensure that the pipeline system is operating at full capacity, and allow overflow during the extremely large flood process.

[0081] In the dry riverbed section, no surface runoff is left, and only extremely large overflow is allowed to enter the dry riverbed to dissipate energy and discharge floods. During the flood season, there is always a dry reservoir on the dam and a long dry riverbed under the dam, which has the best effect in dissipating mountain torrents.

[0082] When facing a particularly large mountain torrent, the system needs to be repaired urgently if necessary. This is mainly for post-flood maintenance of small reservoir dams and dam breaches, and post-flood maintenance of dry riverbed flood control pipes and jungles.

[0083] The technical solution of the present invention is described in detail above in conjunction with the embodiments / drawings, but the present invention is not limited to the above technical solution. For ordinary technicians in this technical field, after knowing the contents recorded in the present invention, they can make several equivalent changes and substitutions without departing from the principle of the present invention. These equivalent changes and substitutions should also be regarded as belonging to the protection scope of the present invention.

Claims

1. A flash flood prevention method based on a combination of dams, pipes and beaches, characterized in that: The flash flood prevention method comprises the following steps: S1. Analyze the influence of the underlying surface characteristics on precipitation based on the underlying surface characteristics of the flash flood control area, and predict the possibility of a major flash flood in the flash flood control area in the future; S2. According to the objectives and requirements of flash flood prevention and control work, combined with the underlying surface characteristics and the possibility of a major flood as described in step S1 and the characteristics of flash flood runoff in the flash flood prevention and control area, at least one flash flood prevention and control system connected in series with the river is constructed on the river into which the flash flood runoff flows. The flash flood prevention and control system comprises a flood control dam constructed on the river course, a flood control reservoir constructed upstream of the flood control dam, a flood control dry riverbed or flood control dry river beach constructed downstream of the flood control dam, and a drainage pipe buried in the flood control dry riverbed or flood control dry river beach. The water inlet of the drainage pipe is arranged at the bottom of the flood control reservoir, and the water outlet is arranged in the river course downstream of the flood control dry riverbed or flood control dry river beach. S3: During the flood season, floods are blocked by flood control dams and stored in dry flood control reservoirs; S4. Determine whether the mountain torrent is a particularly large mountain torrent based on meteorological data. If not, divert the flood through the drainage pipes and reduce the flood through the flood control dry riverbed or flood control dry river beach, leaving no surface runoff. If so, allow the flood in the flood control reservoir to overflow the dam, divert the flood through the drainage pipes, and allow the particularly large overflow to enter the flood control dry riverbed or flood control dry river beach to dissipate energy and discharge the flood. If the overflow causes the flood control dam to fail, the flood control dam must be repaired in a timely manner. S5. After the flood, the flash flood control system is repaired.

2. A flash flood prevention method based on a combination of dams, pipes and beaches according to claim 1, characterized in that: A flood retention and slag blocking forest network and a cross-connected rope network are additionally arranged on the flood control dry riverbed or flood control dry river beach.

3. A flash flood prevention method based on the combination of dams, pipes and beaches according to claim 1, characterized in that: When there are key flood control facilities downstream of a river in a flash flood control area, at least two flash flood control systems connected in series are built upstream of the river to reduce flood peaks and reduce the destructive power of flash floods.

4. A flash flood prevention method based on a combination of dams, pipes and beaches according to claim 1, characterized in that: When the mountain torrent is extremely large, the flood peak can be reduced and the destructive power of the mountain torrent can be reduced by building at least two mountain torrent prevention and control systems connected in series.

5. A method for preventing and controlling mountain torrents based on a combination of dams, pipes and beaches according to claim 3 or 4, characterized in that: When at least two of the above-mentioned flash flood control systems are connected in series, the length and height of the flood control dam backfill area need to be considered: Hn=ζ n-1 eD 80 , Where, L s,n is the length of the silting area in front of the nth flood control dam, in meters, H n is the height of the nth flood control dam, in meters, S init,n is the original ditch bed gradient at the site of the nth flood control dam, expressed as %, determined according to the on-site investigation, ξ is the calculation coefficient, ranging from 0.5 to 0.9, ζ is the calculation coefficient, ranging from 0.6 to 0.8, ε is the calculation coefficient, ranging from 5 to 8, D 80 It is the characteristic particle size of the ditch bed in front of the first flood control dam, in m, determined by on-site investigation.

6. A method for preventing and controlling mountain torrents based on a combination of dams, pipes and beaches according to claim 1, characterized in that: The flood control dam adopts a low and wide dam body, the back water slope is longer and gentler than the front water slope, and it can leak water and overflow the dam.

7. A flash flood prevention method based on a combination of dams, pipes and beaches according to claim 1, characterized in that: The diameter of the drainage pipe is determined based on the multi-year average flow rate of the flood control dry riverbed or flood control dry river beach during the flood season and the pipeline flow rate; the pipe diameter calculation formula is as follows: Where Q is the flow rate in m 3 / h or t / h; D is the inner diameter of the pipe, in meters; V is the average velocity of the fluid, in meters per second.

8. A flash flood prevention method based on a combination of dams, pipes and beaches according to claim 2, characterized in that: The flood retention and slag blocking forest network includes an artificial column group and a tree and shrub forest, wherein the tree and shrub forest is specifically a tree and grass belt, and the average breast diameter of the trees in the tree and grass belt is Dtree> the critical diameter of tree damage D max .

9. A method for preventing and controlling mountain torrents based on a combination of dams, pipes and beaches according to claim 8, characterized in that: The critical diameter of tree destruction is D max It is determined by the following calculation: Where D max is the critical diameter of tree failure, in m; σ is the compressive strength of tree wood along the grain, in kN / m 2 , determined by the tree species; D is the diameter of large debris flow blocks, in meters; h df The depth of debris flow at the site of the flood control dam; F 大块石 、F 泥石流 They are the impact force of large rocks in debris flow and the impact force of debris flow, respectively, the unit is kN, and they are determined by on-site investigation.

10. A flash flood prevention method based on the combination of dams, pipes and beaches according to claim 1, characterized in that: The flood control dry riverbed or flood control dry river beach is selected from a river section or beach covered with a thick gravel layer, and the longer the better.

Images