Method for reducing danger of dammed lake formed by debris flow blocking river

Abstract

A method for reducing the danger of a dammed lake formed by a debris flow blocking a river, comprising: first predicting the accumulation range of a river-blocking debris dam during occurrence of a debris flow, dividing a river boundary into multiple areas on the basis of the elevation, and then performing roughness reduction treatment on the areas of the river boundary during a dry season. The present method reduces the roughness of a river boundary within the accumulation range of a river-blocking debris dam, so as to reduce the opposite bank dam height of the river-blocking debris dam and the storage capacity of the dammed lake, thereby achieving the purpose of reducing the danger of dammed lakes formed by debris flows and reducing the impact of debris flow disasters.

Description

A method to reduce the danger of debris flow blocking rivers and creating barrier lakes Technical Field

[0001] This invention relates to the field of debris flow dammed lake disaster reduction engineering technology, and in particular to a method for reducing the danger of debris flow blocking rivers and dammed lakes. Background Technology

[0002] Debris flow refers to a special type of flood that occurs in mountainous areas or other deep valleys and rugged terrain, triggered by heavy rain, blizzards, or other natural disasters, carrying large amounts of mud, sand, and rocks. Besides the impact and burial hazards during the movement of debris flows, they often present a disaster chain pattern of debris flow blocking a river – creating a barrier lake – a breaching flood, thus amplifying the scope of the disaster. On the one hand, the barrier lake formed by a debris flow blocking a river can cause upstream inundation; on the other hand, the large-scale breaching flood formed after the debris flow barrier lake breaks can cause severe impact and inundation downstream. For example, on October 17, 2018, a large-scale debris flow occurred in the Sedongpu Valley of Milin County, Tibet, blocking the Yarlung Tsangpo River and forming a dam with a height of 77-106m, a width of 3500m, and a reservoir capacity of 30×100m. 6 m 3 The landslide dam breached 56 hours later, with the peak flow reaching 18,000 m³ / h. 3 The mudslide's flow rate of [number] cubic meters per second far exceeded the maximum flood discharge capacity downstream, causing significant losses. Therefore, it is crucial to implement engineering measures to reduce the risk of mudslide-dammed lake-outbreak floods.

[0003] Currently, the commonly used emergency response technology for debris flow dammed lake disaster reduction is blasting and channeling to release water, in order to reduce the water level and reservoir capacity of the dammed lake as much as possible. However, due to the strong plasticity of the dammed body, the effect of blasting and channeling is not obvious. On the other hand, the method of excavating the initial discharge channel poses a great risk of subsidence.

[0004] How to more effectively reduce the danger of debris flow-dammed lakes has become a key research topic.

[0005] Summary of the Invention

[0006] In view of the shortcomings of existing debris flow dammed lake disaster reduction and mitigation methods, the purpose of this invention is to provide a method to reduce the danger of debris flow dammed lakes blocking rivers. The method involves construction during the dry season, which reduces the roughness of the river boundary within the accumulation range of the dammed body, thereby reducing the dam height and reservoir capacity of the dammed lake, thus achieving the goal of reducing the danger of debris flow dammed lakes and mitigating the impact of debris flow disasters.

[0007] This invention provides a method for reducing the danger of debris flows blocking rivers and creating barrier lakes. The method first predicts the accumulation range of the barrier body blocking the river when a debris flow occurs, and divides the river into multiple regions according to the elevation of the river channel boundary. Then, during the dry season, the river channel boundary is subjected to roughening treatment in different regions.

[0008] Furthermore, the division of multiple regions according to the elevation of the river boundary refers to: within the accumulation range of the dammed river body, the river boundary is divided into three sub-regions from low to high according to the river's dry season water level and wet season water level: the first region with an elevation lower than the dry season water level, the second region with an elevation higher than the dry season water level but lower than the wet season water level, and the third region with an elevation higher than the wet season water level.

[0009] The target roughness of the three sub-regions are denoted as n1, n2, and n3, respectively, and satisfy the following:

[0010] The target roughness of the second region n2 < the target roughness of the first region n1 ≤ the target roughness of the third region n3.

[0011] Furthermore, to better realize the present invention, before predicting the accumulation range of the blockage body in the river channel when a debris flow occurs, the debris flow blocking coefficient C is first calculated at the design frequency based on the debris flow blocking discriminant. r Used to determine the debris flow blocking river pattern; when C r If the value is greater than 1.44, it can be concluded that a mudslide will block the river.

[0012] Furthermore, to better realize the present invention, when predicting the deposition range of the dammed river body in the river channel during a debris flow: using 3D design software, a dammed river body model is first generated based on the topographic data of the debris flow channel DEM and the main river channel DEM, at the intersection of the debris flow channel and the main river channel, to simulate the 3D structure of the dammed river body; the 3D structure of the dammed river body includes an upstream dam body, a middle main dam body, and a downstream dam body, with the slope of the top of the middle main dam body sloping from the same bank of the debris flow channel to the opposite bank of the debris flow channel denoted as α. i The slope formed by the top of the upstream dam extending from the middle main dam body upstream of the main river is denoted as α. u The slope formed by the top of the downstream dam extending from the central main dam body downstream of the main river is denoted as α. d Then, the key structural parameters in the three-dimensional structure of the dammed river are set: the top width B of the intermediate main dam body and the top slope α of the intermediate main dam body are set. i The upstream slope α of the blockage dam body u The downstream slope α of the landslide dam is... dThe morphological characteristics of the gully are known quantities with definite values, thus obtaining a set of variables X that vary with the total volume V of the dammed river. These variables X consist of the total height H and the total length L of the dammed river. Finally, the total volume Vc of the primary debris flow at the predicted design frequency is obtained. Under the constraint that "the total volume V of the dammed river is equal to the total volume Vc of the primary debris flow at the design frequency", a set of corresponding total height H and total length L of the dammed river are solved. Combined with the DEM of the debris flow gully and the DEM of the main river channel, the predicted deposition range of the dammed river in the river channel is obtained.

[0013] Furthermore, in order to better realize the present invention, the channel morphology features are extracted from the debris flow channel DEM and the main river channel DEM;

[0014] The top width B of the intermediate main dam body is also the top width of the dam of the river-blocking dam body, which is equal to the width b of the outlet of the debris flow channel, i.e., B = b.

[0015] The top slope α of the intermediate main dam body i The value is taken according to the longitudinal sedimentation gradient i of the dammed river body, which is j times the longitudinal gradient γ of the debris flow channel, i.e., α i =i=γ*j, j∈(0.5,0.8);

[0016] The upstream slope α of the blockage dam is... u The angle of repose β of the mudflow is equal to that of the natural mudflow, i.e., α u =β;

[0017] The downstream slope α of the blockage dam is... d , satisfying: α d =k*α u =k*β, k∈(0,1); where k is the slope reduction coefficient of the downstream of the dam under the action of the main river flow;

[0018] The height H of the opposite bank dam of the intermediate main dam body D The dam height H on the same bank as the intermediate main dam body S Satisfy: H S =(1+α) i )*H D And H S ≤hs、H D ≤h D Among them, H S ≤hs represents the same-bank dam height H of the intermediate main dam body. S H does not exceed the same bank height hs of the main channel. D ≤h D The height H of the intermediate main dam body on different banks is indicated. D The height h of the opposite bank of the main channel does not exceed D .

[0019] The total length L of the dammed river is the horizontal span from the lowest point of the upstream dam body to the lowest point of the downstream dam body. It is used to characterize the length of the dammed river in the river channel when a debris flow occurs, and also to characterize the length of the construction area during the roughening construction.

[0020] The beneficial effects of this invention are as follows.

[0021] (1) The present invention provides a method for reducing the danger of debris flow blocking rivers and landslide dams. By reducing the roughness of the river boundary within the accumulation range of the blockage body, the height of the opposite bank of the blockage body and the reservoir capacity of the landslide dam are reduced, thereby reducing the danger of debris flow blocking lakes and reducing the impact of debris flow disasters.

[0022] (2) The present invention provides a method to reduce the danger of debris flow blocking rivers and damming lakes. Construction is carried out during the dry season, which greatly reduces the construction difficulty and cost.

[0023] (3) The present invention provides a method for reducing the danger of debris flow blocking rivers and damming lakes, and designs different target roughness for different regions to suit local conditions.

[0024] (4) The present invention provides a method to reduce the danger of debris flow blocking rivers and dammed lakes. The method is to assess and implement the method before the debris flow blocks the river. Compared with the previous method of emergency response after the blockage occurs, this method is a pre-emptive prevention measure with ample time for response. Attached Figure Description

[0025] Figure 1 is a schematic diagram of a longitudinal section of the dammed body model in the main river channel.

[0026] Figure 2 is a schematic cross-sectional view of a model of a dammed body blocking the river in the main channel.

[0027] Figure 3 is a schematic diagram of the accumulation range and cross-sectional division of the dammed river when viewed from above.

[0028] Figure 4 is a schematic diagram showing the position of the cross section in Figure 3 on the longitudinal section of the dammed river model.

[0029] Figure 5 is a schematic diagram showing the locations of multiple longitudinal sections obtained along the main river direction when viewed from above.

[0030] In the diagram, 100 represents the debris flow channel; 200 represents the main river channel; 300 represents the model of the river dam; Q1 represents the first region; Q21 represents the same-bank portion of the debris flow channel in the second region; Q22 represents the opposite-bank portion of the debris flow channel in the second region; Q31 represents the same-bank portion of the debris flow channel in the third region; and Q32 represents the opposite-bank portion of the debris flow channel in the third region. Detailed Implementation

[0031] The following detailed description, in conjunction with specific embodiments, further illustrates the above-described content of the present invention. However, this should not be construed as limiting the scope of the present invention to the following examples. Various substitutions or modifications made based on ordinary technical knowledge and conventional methods in the art without departing from the above-described technical concept of the present invention should be included within the scope of the present invention.

[0032] Example 1:

[0033] This embodiment provides a method to reduce the danger of debris flow blocking rivers and dammed lakes. First, the accumulation range of the blockage body when the debris flow occurs is predicted, and multiple areas are divided according to the elevation of the river boundary. Then, during the dry season, the river boundary is divided into areas for roughening treatment.

[0034] The method is implemented during the dry season. By reducing the roughness of the river boundary within the accumulation range of the landslide dam, the height of the landslide dam and the capacity of the landslide lake are reduced, thereby reducing the danger of debris flow landslide lakes and mitigating the impact of debris flow disasters.

[0035] A key point of the method described in this embodiment is that the roughness reduction construction is carried out during the dry season.

[0036] River levels are lower during the dry season and higher during the wet season. The dry and wet season water levels at various cross-sections of the river can be estimated using the Manning formula from "Li Wei. Hydraulic Calculation Handbook (Second Edition) [M]. Beijing: China Water Resources and Hydropower Press, 2006." They can also be predicted based on historical river level changes, or other methods can be used to determine the dry and wet season water levels. The estimated or predicted dry and wet season water levels are used in the design of roughness reduction construction.

[0037] Regarding the dry season, the dry season of the construction year is usually predicted based on the historical occurrence of the dry season in the river channel, and the dry season schedule is then determined based on the predicted dry season. Scheduling the construction based on the construction time requirements is not an innovative point of this application; existing scheduling methods can be used, so it will not be elaborated further.

[0038] Another key point of the method described in this embodiment is that multiple areas with different roughness reduction requirements are divided according to the elevation of the river boundary.

[0039] The inherent topographic features and roughness of river boundaries at different elevations are different. Considering the characteristics of debris flow impact forming river dams, different target roughnesses are designed for river boundary areas at different elevations. This approach is tailored to local conditions, taking into account both the social benefits of disaster prevention and mitigation and the economic benefits of strictly controlling construction costs. It can reduce the height of the dam and the capacity of the landslide dam lake, while also fully considering the economic benefits of the project.

[0040] Example 2:

[0041] This embodiment is an optimization based on Embodiment 1.

[0042] First, when conducting an investigation and research on a certain location, it is necessary to determine the extent of river blockage caused by the mudslide. If the blockage is minor, then roughening construction may not be necessary; if the blockage is severe, then roughening construction is required.

[0043] Secondly, after determining that roughness reduction construction is required, the approximate location of the dammed river needs to be identified, and the area for roughness reduction construction should be determined based on the accumulation area of ​​the dammed river. After determining the area for roughness reduction construction, the river boundary is divided into multiple sub-regions according to elevation. According to the elevation from low to high, the target roughness of each sub-region generally shows that the target roughness of the central sub-region is high, while the target roughness of the top and bottom sub-regions is low.

[0044] Finally, during the dry season, construction is carried out according to the target roughness of each sub-area.

[0045] In another specific embodiment, a method for quantitatively determining the degree of river blockage is provided. Specifically, before predicting the accumulation range of the blockage dammed body at the time of a debris flow, the debris flow blockage coefficient C is calculated at the design frequency based on the debris flow blockage discriminant formula. r Used to determine the debris flow blocking river pattern; when C r If the value is greater than 1.44, it can be concluded that a mudslide will block the river.

[0046] In another specific embodiment, the proposed debris flow-induced dam is located at the confluence of the debris flow channel 100 and the main river channel 200. As shown in Figure 3, the debris flow rushes from the debris flow channel 100 into the main river channel 200, gradually accumulating to form the dam. This dam first accumulates near the debris flow channel 100, and then spreads and accumulates upstream and downstream of the main river. In this case, the method described in Embodiment 1 involves roughening construction in the main river channel 200 to reduce the roughness of the main river channel 200 within the accumulation range of the dam.

[0047] After determining the location and deposition area of ​​the landslide dam in the main channel 200, the boundary of the main channel 200 was divided into multiple sub-regions according to elevation.

[0048] Dividing the river boundary into multiple sub-regions based on elevation means that, within the depositional area of ​​the dammed river, the river boundary is divided into three sub-regions from low to high according to the river's low-water and high-water levels: the first region Q1, whose elevation is lower than the low-water level; the second region, whose elevation is higher than the low-water level but lower than the high-water level; and the third region, whose elevation is higher than the high-water level.

[0049] Figures 1 and 4 are schematic longitudinal sections of a simulated river dam in the main channel 200. From the perspective of river channel elevation, the first region Q1, the second region, and the third region rise in elevation. Looking at the left and right banks of the main channel 200, the first region Q1 is located in the middle of the river. Extending from the first region Q1 towards any bank of the main channel 200, it corresponds sequentially to the second and third regions. Furthermore, the river boundaries of the second and third regions are both divided into two parts according to the left and right banks, forming: the same-bank portion of the debris flow gully in the second region Q21, the opposite-bank portion of the debris flow gully in the second region Q22, the same-bank portion of the debris flow gully in the third region Q31, and the opposite-bank portion of the debris flow gully in the third region Q32.

[0050] The target roughness of the three sub-regions are denoted as n1, n2, and n3, respectively, and satisfy the following:

[0051] The target roughness of the second region n2 < the target roughness of the first region n1 ≤ the target roughness of the third region n3. At this time, the target roughness of the debris flow gully on the same bank Q21 and the debris flow gully on the opposite bank Q22 in the second region is n2; the target roughness of the debris flow gully on the same bank Q31 and the debris flow gully on the opposite bank Q32 in the third region is n3.

[0052] Furthermore, the target roughness n1 of the first region Q1 is selected with reference to the roughness of natural river channels in plains, clean, straight rivers without shallows or deep pools. When performing roughness reduction treatment on the first region Q1, obstacles that hinder water flow are removed, and rugged areas are smoothed by excavation and filling.

[0053] Furthermore, the target roughness n2 of the second region is selected with reference to the roughness of the artificial channel. When performing roughness reduction treatment on the second region, firstly, obstacles that hinder water flow are removed, then the areas with abrupt changes in terrain are leveled by excavation and filling, and finally, concrete is used to solidify the region, forming a smooth concrete revetment at the river boundary of the second region.

[0054] Furthermore, the target roughness n3 of the third region is selected with reference to the hydraulic calculation manual and T / CAGHP 006-2018 Debris Flow Disaster Prevention Engineering Investigation Specification (Trial). When performing roughness reduction treatment on the third region, obstacles hindering water flow are removed, and rugged areas are smoothed by excavation and filling.

[0055] Example 3:

[0056] This embodiment is an optimization based on embodiment 1 or embodiment 2.

[0057] Chinese invention patent application CN110955952A discloses a multi-scale debris flow hazard assessment method, which comprehensively studies three spatial scales: major disaster points, typical road sections, and a large area along the entire route, exploring methods for analyzing debris flow hazard at different scales. Chinese invention patent application CN108090670A discloses a method for obtaining landslide volume through empirical formulas. Chinese invention patent application CN115393716A discloses a method for calculating the area and volume of a landslide dam using digital elevation model data via a GIS platform, and also discloses a method for calculating the volume of landslide bodies and landslide dams based on empirical formulas. Besides GIS platforms, the volume of a specified model can also be obtained through the DTM analysis module in MapGIS software, or through the MASSPROP module in CAD software. Based on the above existing technologies, after determining the three-dimensional structure of the landslide dam, the total volume of the landslide dam can be obtained through empirical methods and model volume calculation methods.

[0058] In this embodiment, the determination is made using 3D design software with 3D modeling and 3D solid volume analysis functions, specifically including the following steps Sa, Sb, and Sc.

[0059] Step Sa: First, determine the three-dimensional structure of the river dam and the key structural parameters within that structure.

[0060] In this embodiment, as shown in Figure 2, the three-dimensional structure of the river dam in the dam model 300 includes the upstream dam body, the intermediate main dam body, and the downstream dam body.

[0061] The key structural parameters in the three-dimensional structure of the aforementioned landslide dam include the top width B of the intermediate main dam body and the top slope α of the intermediate main dam body. i The upstream slope α of the blockage dam body u The downstream slope α of the landslide dam is... d The total height H of the dammed river blockage, and the height H of the opposite bank dam of the intermediate main dam. D The height H of the dam on the same bank of the main dam body in the middle S The data includes the total length L of the dammed river and the morphological characteristics of the channel. Among these, the channel morphological characteristics are described using a channel morphology dataset to depict the spatial structure of the channel boundary region. Since the channel morphological characteristics are extracted from the debris flow channel DEM and the main channel DEM, x is used as the data source. DEM express.

[0062] When constructing the 300 model of the river dam, based on the stability state of the river dam structure, the top width B and top slope α of the intermediate main dam body in the key structural parameters are included. i The upstream slope α of the blockage dam bodyu The downstream slope α of the landslide dam is... d The morphological characteristics of the gully are used as known quantities with fixed values, while the total height H and total length L of the dammed river are used as variables affecting the total volume V of the dammed river. To facilitate modeling, temporary preset values ​​are first set for the total height H and total length L of the dammed river.

[0063] In this embodiment, the values ​​of some key structural parameters are determined as follows:

[0064] As shown in Figures 2 and 3, the top width B of the intermediate main dam body is also the top width of the dam of the river blocking dam body, which is equal to the outlet width b of the debris flow channel 100, i.e., B = b.

[0065] The top slope α of the intermediate main dam body i The value is taken according to the longitudinal sedimentation gradient i of the dammed river body, which is j times the longitudinal gradient γ of the debris flow channel, i.e., α i =i=γ*j, j∈(0.5,0.8);

[0066] As shown in Figure 2, the upstream slope α of the blockage dam is... u The angle of repose β of the mudflow is equal to that of the natural mudflow, i.e., α u =β;

[0067] As shown in Figure 2, the downstream slope α of the landslide dam is... d , satisfying: α d =k*α u = k*β, k∈(0,1); where k is the downstream slope reduction coefficient of the dam body under the action of the main river flow.

[0068] It should be noted that other methods can also be used to confirm the top width B and top slope α of the intermediate main dam body. i The upstream slope α of the blockage dam body u The downstream slope α of the landslide dam is... d The specific values ​​of key structural parameters such as channel morphology and characteristics can be adjusted by those skilled in the art based on the actual situation, as long as the operational approach of subsequent steps is not changed, and therefore will not be elaborated upon.

[0069] Step Sb: Then, obtain the correspondence between the total volume V of the river dam and the total height H and total length L of the river dam.

[0070] The total length L of the river dam is explained. The total length L of the river dam is the horizontal span from the lowest point of the upstream dam body to the lowest point of the downstream dam body, used to characterize the length of the dammed body accumulated in the river channel during a debris flow. As shown in Figure 3, it is mainly composed of the span L of the upstream dam body. u The intermediate main dam body, the top width of the intermediate main dam body (B), and the span of the downstream dam body (L) d It consists of three parts; although the total length L of the dammed river is not numerically determined, it is related to the total height H of the dammed river, the top width B of the intermediate main dam, and the top slope α of the intermediate main dam. i The upstream slope α of the blockage dam body u The downstream slope α of the landslide dam is... d Variables related to channel morphology are represented as L = f(H, B, α) i α u α d x DEM Based on B, α i α u α d x DEM Since all of these are known quantities with definite numerical values, in this embodiment, the total height H of the river dam is used as the independent variable, and the total length L of the river dam is used as the dependent variable that varies with the total height H of the river dam.

[0071] The total height H of the landslide dam is explained. Although the exact value of the total height H of the landslide dam is uncertain, it is related to the height H of the opposite bank dam of the main dam in the middle. D The height H of the dam on the same bank of the main dam body in the middle S Related. The height H of the dam on the opposite bank of the intermediate main dam body. D The total height H of the dammed river is [missing information]. On the other hand, the height H of the opposite bank dam of the intermediate main dam body is [missing information]. D The dam height H on the same bank as the main dam body in the middle S Satisfy: H S =(1+α) i )*H D Furthermore, the height H of the dam on the same bank of the main dam in the middle is... S The same-bank height hs not exceeding 200 meters of the main channel, and the opposite-bank dam height H of the intermediate main dam body. D The height h of the opposite bank does not exceed 200 mm of the main channel. D .

[0072] Among them, the height h of the opposite bank of the main channel is 200. D The same-bank height hs of the main channel 200, and the opposite-bank dam height H of the intermediate main dam body. D The height H of the dam on the same bank of the main dam body in the middle SIn this context, "same bank" and "different bank" refer to the debris flow channel 100 as a reference point. The side closer to the debris flow channel 100 is considered "same bank," and the side farther from the debris flow channel 100 is considered "different bank." As shown in Figures 1 and 4, in the longitudinal section of the intermediate main dam body perpendicular to the main river direction, the height difference between the intersection of the top of the intermediate main dam body and the different bank of the main river channel 200 and the bottom of the main river channel 200 is taken as the different bank dam height H of the intermediate main dam body. D However, the height H of the dam on the opposite bank of the main dam body in the middle is... D The method for determining the value is not limited to this; the average height difference between the top edge of the intermediate main dam body and the bottom of the main channel (200 meters) can also be selected as the cross-bank dam height H of the intermediate main dam body. D The numerical value; those skilled in the art can also use other methods to determine the specific value according to the actual situation and conventional methods. As long as the overall technical concept of this embodiment is not changed, they are all included in the solution of this embodiment, so they will not be described in detail.

[0073] This embodiment uses the "height H of the intermediate main dam body on different banks" as an example. D Taking the total height H of the river dam as an example, we can illustrate the constraints on the value of the total height H of the river dam. In this case, the maximum value of the total height H of the river dam is denoted as Hmax, where H∈(0,Hmax]; the constraint condition is: Hmax≤h D And (1+α) i Hmax ≤ hs. Where hs is the same-bank elevation of 200m in the main channel, and h is the opposite-bank elevation of 200m in the main channel. D Extracted from the main channel DEM.

[0074] Furthermore, depending on the specific protection requirements, an additional dam height limit coefficient θ, where θ∈(0.7,1), will be added in practice. The corresponding constraint condition is: Hmax≤θ*h D And (1+α) i )*Hmax≤θ*hs.

[0075] The method for obtaining the relationship between the total volume V of the landslide dam and its total height H and total length L is explained. After the structural parameters of the landslide dam model 300 are determined, the model is discretized using computer software, dividing the complex geometry into many smaller geometric shapes. The volume of each smaller geometric shape is then calculated and summed to obtain the volume of the entire entity, i.e., the total volume of the landslide dam. Therefore, based on the determined three-dimensional structure of the landslide dam and its key structural parameters, the total height H and total length L of the landslide dam are treated as a set of variables X. The correspondence between these variables and the total volume V can be represented by V = f(H,L). Based on the known quantities in step Sa, a set of total height H, total length L, and corresponding total volume V of the landslide dam constitutes a data item. Several data items form a dataset Y reflecting V = f(H,L).

[0076] Step Sc: Obtain the total volume Vc of a primary debris flow at the predicted design frequency, and under the constraint that "the total volume V of the dammed river is equal to the total volume Vc of a primary debris flow at the design frequency", solve for a set of corresponding total height H and total length L of the dammed river.

[0077] Based on the dataset Y obtained in step Sb, we only need to search in dataset Y under the condition of "V=Vc" to obtain the total height H and total length L of the dammed river body that meet the conditions, thereby determining the accumulation range of the dammed river body when the debris flow occurs, and then determining the area to be dredged for construction.

[0078] In this embodiment, a model 300 of the dammed river is first constructed. By combining the debris flow channel DEM, the main channel DEM, geomorphological and hydrological data with empirical values, the aforementioned outlet width b, the same-bank height hs of the main channel 200, and the opposite-bank height h of the main channel 200 can be confirmed. D The natural angle of repose of debris flow β, the downstream slope reduction factor k of the dam under the action of the main river flow, the longitudinal gradient γ of the debris flow channel, the dam height limitation factor θ, and the river channel morphology characteristics x DEM Parameters such as V and H are obtained; then, using the 3D solid volume analysis function in the 3D design software, the dataset Y corresponding to the total volume V of the dammed river, the total height H of the dammed river, and the total length L of the dammed river is obtained; then, using the condition "V = Vc", the corresponding total height H and total length L of the dammed river are found from the dataset Y, thus determining the deposition range of the dammed river in the river channel when the debris flow occurs, and thus determining the area to be de-roughened.

[0079] In another specific embodiment, the total length L of the dammed river is used as the length of the first region Q1 along the main river direction, and also as the length of the second region along the main river direction. As for the length of the third region along the main river direction, an empirical method is usually used, where the total length L of the dammed river is appropriately reduced to serve as the length of the third region along the main river direction.

[0080] Example 4:

[0081] Compared to Example 3, this example also requires 3D design software with 3D modeling and 3D solid volume analysis capabilities, but the method for obtaining V = f(H,L) is different. This example provides a method based on the idea of ​​piecewise accumulation to obtain the correspondence between the total volume V of the river dam and the total height H and total length L of the river dam. This method includes the following steps: Ta, Tb, and Tc.

[0082] Step Ta, as shown in Figure 3, involves constructing a dammed river model 300 at the confluence of debris flow channel 100 and main river channel 200 based on the measured topography, and determining the three-dimensional structure and key structural parameters of the dammed river.

[0083] The three-dimensional structure of the landslide dam in the model 300 includes the upstream dam body, the intermediate main dam body, and the downstream dam body. When constructing the model 300, based on the stability state of the landslide dam structure, the top width B and top slope α of the intermediate main dam body are included in the key structural parameters. i The upstream slope α of the blockage dam body u The downstream slope α of the landslide dam is... d The morphological characteristics of the channel are used as known quantities with fixed values. The total height H and total length L of the dammed river are used as variables affecting the total volume V of the dammed river. For ease of modeling, a temporary preset value is set for the total height H of the dammed river during modeling. Steps Ta and Sa are the same and will not be described again.

[0084] Step Tb, as shown in Figures 3 and 4, firstly, based on the measured topography, the dam body is sequentially cut at equal intervals from the opposite bank away from the debris flow channel 100 to the same bank closer to the debris flow channel 100, forming a set of cross sections, denoted as: cross section 1-1, cross section 2-2, cross section 3-3, ..., cross section (n-2)-(n-2), cross section (n-1)-(n-1), cross section nn; where n is a positive integer not less than 3; the distance between adjacent cross sections is denoted as ΔL. This set of cross sections is along the main river direction and perpendicular to the middle main dam body of the dam body. The specific value of the distance ΔL between adjacent cross sections is determined according to the accuracy requirements. Secondly, using 3D design software, based on the top width B and top slope α of the middle main dam body determined in step Ta, the cross sections are cut at equal intervals. iThe upstream slope α of the blockage dam body u The downstream slope α of the landslide dam is... d Based on the morphological characteristics of the gully and the total height H of the temporarily constructed river-blocking dam, determine the intersection points of the aforementioned cross-sections with the terrain, such as: 1, 2 u 2 d ... n u n d Connect all intersection points smoothly in sequence to form a closed region; this closed region is the planar accumulation area of ​​the river dam, and the maximum span of this closed region along the main river direction is the total length L of the river dam. Then, calculate the area of ​​each cross-section, and use the cumulative summation method to obtain the total height H and the total volume V of the river dam corresponding to the total length L of this group of river dams. Assuming different total heights H of the river dams, obtain multiple sets of corresponding total volumes V and total lengths L of the river dams.

[0085] Figure 3 illustrates the aforementioned cross-sections and their intersections with the terrain. Based on the cross-section division method in step Tb, in most cases, when a cross-section intersects with the terrain, two intersection points are formed: one in the upstream area of ​​the main river and one in the downstream area. For example, the intersection point n of cross-section nn with the upstream area of ​​the main river in the terrain. u The intersection point n with the downstream area of ​​the main river in the terrain. d In special cases, a cross section may intersect with the terrain at only one point, such as when cross section 1-1 intersects with the terrain to form point 1. This is only because the intersection of the cross section with the upstream area of ​​the main river and the intersection with the downstream area of ​​the main river happen to coincide.

[0086] Step Tc: Obtain the total volume Vc of a primary debris flow at the predicted design frequency, and under the constraint that "the total volume V of the dammed river is equal to the total volume Vc of a primary debris flow at the design frequency", solve for a set of corresponding total height H and total length L of the dammed river.

[0087] The other parts of this embodiment are the same as those in Embodiment 1, Embodiment 2 or Embodiment 3, so they will not be described again.

[0088] Example 5:

[0089] This embodiment is based on embodiment 4.

[0090] A method to reduce the danger of debris flow blocking rivers and creating barrier lakes includes three main parts: debris flow blocking model assessment, roughness reduction scheme design, and roughness reduction scheme implementation.

[0091] I. Judgment of the debris flow blocking river pattern.

[0092] This embodiment provides a method for determining whether a debris flow will block a river. The Chen Deming formula recorded in "Chen Deming, Wang Zhaoyin, He Yun. Experimental study on the impact of debris flow on rivers [J]. Sediment Research, 2002(03):22-28" is used as the discriminant for debris flow blocking a river to determine whether a debris flow will block a river.

[0093] Chen Deming's formula:

[0094] C r Represents the mudslide blocking coefficient; when C r When the value is greater than 1.44, a river blockage will occur; otherwise, the river blockage will not occur.

[0095] γ d This indicates the unit weight of debris flow; it is usually obtained according to the methods specified in the "Specifications for Investigation of Debris Flow Disaster Prevention and Control Engineering".

[0096] γ m This represents the unit weight of the main river flow; it is usually taken as 10.0 kN / m³. 3 ;

[0097] Q d The debris flow rate is usually obtained according to the methods in the "Specifications for Investigation of Debris Flow Disaster Prevention and Control Engineering";

[0098] Q m The flow rate of the main river is usually obtained based on historical measurements from hydrological stations or on-site measurements.

[0099] v d This represents the average velocity of a debris flow; it is usually obtained according to the methods specified in the "Specifications for Investigation of Debris Flow Disaster Prevention and Control Engineering".

[0100] v m This indicates the average flow velocity of the main river; it is usually obtained based on historical measurements from hydrological stations or on-site measurements.

[0101] α represents the confluence angle; it is usually obtained from field surveys or remote sensing imagery.

[0102] Based on the aforementioned discrimination formula for debris flow blocking rivers, the basic parameters of debris flows at the design frequency are used for judgment. If it is determined that there will be no river blockage, the risk is considered very low, because no blockage is equivalent to not completely cutting off the river; it will only temporarily impound the upstream water level, and the maximum impoundment level is generally very small. If it is determined that river blockage will occur, the dammed body poses a high risk, with a high probability of upstream inundation and downstream breach flooding. Therefore, some measures need to be taken to reduce the danger of the dammed body. Typically, the parameter values ​​of the design frequency are consistent with the prevention and control standards of the debris flow channel control project.

[0103] Furthermore, other methods such as numerical simulation can be used to assess the likelihood of river blockage, as long as it can be determined whether a debris flow will occur and block the river. Only when a debris flow is predicted to block the river should subsequent roughness reduction schemes be designed and implemented.

[0104] II. Roughness Reduction Scheme Design.

[0105] Structural parameters of the confluence area of ​​debris flow channel 100 and main river channel 200 were obtained to create a 3D model of the dammed river. The cross-section formed along the main river direction is the transverse direction of the dammed river; the longitudinal section formed perpendicular to the main river direction is the longitudinal direction of the dammed river.

[0106] First, assign values ​​to the main structural parameters of the dammed river.

[0107] The width b of the outlet of the debris flow channel 100 is regarded as the top width B of the intermediate main dam body.

[0108] Because the landslide dam formed by the debris flow was naturally deposited, the upstream slope α of the landslide dam is... u Take the natural angle of repose β of the mud-rock fluid, as shown in Equation 2: αu=β Equation 2

[0109] β is the natural repose angle of debris flow. Its value is obtained by selecting a 100mm source soil sample from the debris flow channel through field investigation. If there are historical debris flow remnants, select the remnant soil sample. Then, add water to the soil sample to achieve the debris flow unit weight at the design frequency. Slowly pour the prepared debris flow sample onto the ground to allow it to accumulate slowly. After it stabilizes, measure the slope of the accumulation body, which is the natural repose angle β of the debris flow.

[0110] During the process of blocking the river, some of the solid debris from the mudslide will be transported downstream due to erosion by the main river flow. Therefore, the downstream slope α of the dam body of the river-blocking dam is... d The upstream dam slope α is lower than that of the blockage dam. u The slope reduction factor k of the downstream slope of the landslide dam under the action of the main river flow is used for conversion, as shown in Equation 3: αd=kβ Equation 3

[0111] Where k is the slope reduction coefficient of the downstream slope of the dam under the action of the main river flow, and k∈(0,1); usually, the value of k is taken as 0.6-0.9 based on experience.

[0112] Second, the dammed river body was cut into multiple parallel cross-sections.

[0113] Based on the measured topography of the main river channel 200, as shown in Figure 4, the height H of the opposite bank dam of the central main dam body is taken as... DAs the total height H of the dammed river, it is divided into sections at equal intervals from the opposite bank of the dammed river, perpendicular to the main debris flow channel, and directed toward the same bank of the channel. These sections are denoted as: section 1-1, section 2-2, section 3-3, ..., section (n-2)-(n-2), section (n-1)-(n-1), and section nn; where n is a positive integer not less than 3.

[0114] Third, determine the structural parameters of several parallel cross-sections of the dammed river body in order to solve for the area of ​​each cross-section.

[0115] The structural parameters of several parallel cross-sections of the dammed river can be obtained through on-site surveying. The outlines of each cross-section of the dammed river are matched with the cross-sectional profile of the main channel (200 mm), and the area of ​​each cross-section is estimated using existing grid methods and fuzzy testing. The area of ​​several cross-sections of the dammed river can also be simplified into quadrilaterals based on on-site measurement data before area estimation. The longitudinal gradient i of the backfilling of the dammed river is generally taken empirically as 0.5-0.8 times the longitudinal gradient of the channel. The method for obtaining the area of ​​each cross-section of the dammed river is not a major improvement in this embodiment; existing technologies can be used to obtain the values, so it will not be elaborated further.

[0116] Fourth, taking the total volume V of the dammed river as equal to the total volume Vc of a single debris flow at the design frequency as the control condition, solve for the corresponding total height H and total length L of the dammed river.

[0117] Calculate the total volume V of the river dam using Equation 4:

[0118] In the formula, V is the total volume of the dammed river.

[0119] ΔL is the distance between adjacent cross sections;

[0120] A n Let n be the cross-sectional area of ​​section n;

[0121] A n-1 Let be the cross-sectional area of ​​section (n-1)-(n-1).

[0122] A represents a general parameter for the cross-sectional area of ​​each section of the river dam, with its subscript indicating the section number; for example, A1 represents the cross-sectional area of ​​section 1-1; A n Let n be the cross-sectional area of ​​section n.

[0123] When ΔL is not substituted with a specific value, the total volume V of the dammed river obtained by Equation 4 is an expression for the distance ΔL between adjacent cross sections; the distance ΔL between adjacent cross sections can be determined according to accuracy requirements. After determining the value of the distance ΔL between adjacent cross sections, assuming different total heights H of the dammed river, multiple sets of different cross-sectional areas of the dammed river will be obtained, and then the total volume V of different dammed river sections can be calculated. When V = V c At this time, the total height H of the corresponding river-blocking dam body is the predicted dam height under the design conditions. At this time, the cross-section of each river-blocking dam body will intersect with the terrain, as shown in Figure 3: 1, 2 u 2 d ... n u n d After smoothly connecting these intersections in sequence, the enclosed area is the accumulation range of the landslide dam.

[0124] In this embodiment, the total length L of the dammed river is used as the length of the first region Q1 along the main river direction, and also as the length of the second region along the main river direction. As for the length of the third region along the main river direction, an empirical method is typically used, where the total length L of the dammed river is appropriately reduced to represent the length of the third region along the main river direction. Of course, those skilled in the art can also adjust the scope of the roughening construction area based on the total length L of the dammed river according to actual needs, either expanding or shrinking it.

[0125] It should be noted that when determining the main river's flood control area, changes in river level are not considered, i.e., whether it is during the high-water season is not taken into account.

[0126] III. Implementation of the Roughness Reduction Plan

[0127] In this embodiment, different roughness reduction methods are used in different areas within the debris flow deposition range.

[0128] Zone Q1: This area is below the water level during the dry season. There is always flowing water in this area, and it is underwater, making it difficult to solidify. However, there are usually some large rocks and boulders in the river that seriously obstruct the flow of water. Excavators and other mechanical equipment are used to remove them, and the terrain is appropriately smoothed in areas with abrupt changes and ruggedness.

[0129] After processing using this method, the roughness of this section can be selected by referring to the roughness of natural river channels in plains, clean, straight rivers without shallows or deep pools, as shown in Table 1:

[0130] Table 1

[0131] The second zone is the area between the high-water and low-water levels, including: the section of the debris flow gully on the same bank (Q21) and the section on the opposite bank (Q22) of the debris flow gully in the second zone. Water flows through this area only during the high-water season, which is also the period of most debris flow outbreaks. First, it is necessary to remove objects that severely obstruct water flow in this area, such as large rocks, boulders, and driftwood. Second, areas with abrupt changes in terrain and ruggedness should be leveled by excavation and filling. Finally, the area should be solidified using methods such as concrete or masonry, ensuring the surface is as smooth as possible.

[0132] After processing using this method, the roughness of this section can be selected with reference to the roughness of artificial channels, as shown in Table 2:

[0133] Table 2

[0134] The third region is the area covered by the dammed river above the high-water level during the rainy season. It includes the same-bank portion (Q31) and the opposite-bank portion (Q32) of the debris flow gully in the third region. No river flow passes through this area; only debris flow comes into contact with it. Only large rocks, boulders, and driftwood remaining on the surface need to be removed, and areas with abrupt changes in terrain should be appropriately modified to reduce surface resistance to debris flows. After this treatment, the roughness of this section can be selected with reference to the hydraulic calculation manual and the debris flow disaster prevention engineering survey specifications. The uncorrected river roughness should be selected according to the natural river roughness table in the hydraulic calculation manual.

[0135] After processing the above regions, the roughness of each region will be significantly reduced compared to before processing. The roughness relationship of each region is as follows: the target roughness of the second region n2 < the target roughness of the first region Q1 n1 ≤ the target roughness of the third region n3.

[0136] Furthermore, in order to increase the dry area for construction, reduce construction difficulty, save project investment, and maximize construction results, the roughness reduction construction needs to be carried out during the dry season when the river water level is at its lowest.

[0137] The other parts of this embodiment are the same as those in embodiment 4, so they will not be described again.

[0138] Example 6:

[0139] This embodiment is based on Embodiments 1-5, and is described in detail in conjunction with the actual engineering situation.

[0140] Project details: A debris flow gully exists in a certain area. The overall watershed slopes from south to north, with a relative elevation difference of 1307 meters. The main channel of debris flow gully 100 is 7.96 km long, and its area is 17.0 km². 2The longitudinal gradient of the debris flow channel is 164‰, and the width of the outlet (b) is 15m. According to the debris flow risk assessment, this debris flow channel is in the "mature stage" of its development, with a debris flow susceptibility level of "prone" and a debris flow activity intensity of "relatively strong." Based on a 20-year return period (P=5%), the total debris flow volume V is estimated to be... c Approximately 3.34 × 10 4 m 3 Debris flow rate Q d 110m 3 / s, average velocity of debris flow v d The velocity is 8.60 m / s, and the unit weight of debris flow is γ. d 20.5 kN / m 3 The debris flow channel 100 intersects a river, with a confluence angle α of 90°. Numerous important facilities such as farmland, roads, and houses are located along both sides of the river within a 3km radius upstream and downstream of the confluence area. If a debris flow blocks the river, it could cause severe damage, including upstream inundation and downstream breach flooding. Under a 20-year return period (P = 5%), the main river flow Q... m 180m 3 / s, average flow velocity of the main river v m The flow rate is 4.50 m / s, and the unit weight of the main river flow is γ. m 10.0 kN / m 3 The main river's flow rate during the high-water season is 180 m³. 3 / s, with a flow rate of 50m³ / s during the dry season. 3 / s; the original roughness of the main channel 200 is 0.045, and the average longitudinal slope of the main channel 200 is 10‰.

[0141] Based on the prevention and control standard of once every 20 years (P=5%), the above basic parameters are substituted into Equation 1 for judgment:

[0142] The calculated value is Cr = 2.39.

[0143] Because Cr > 1.44, it is determined that river blockage will occur. Since river blockage poses a high risk, the roughness reduction method proposed in this invention is needed to reduce the danger of the blockage.

[0144] Based on the three-dimensional model of the river dam constructed in Example 3, Example 4, or Example 5, as well as measured data, the main structural parameters of the river dam were determined.

[0145] First, based on the outlet width b of the debris flow channel 100, the top width B of the intermediate main dam is calculated to be 15m. Second, through field investigation, it was found that relatively well-preserved historical debris flow remnants exist near the outlet of the debris flow channel. Therefore, some of these remnants were excavated, water was added, and the debris flow unit weight γ at the design frequency was adjusted. d20.5kN / m 3 The prepared debris flow sample was slowly poured onto the ground to allow it to accumulate gradually. After stabilization, the slope of the accumulated mass was measured to be 15°, which is the natural angle of repose of the debris flow, β = 15°. Based on experience, the downstream slope reduction factor k of the dam under the action of the main river flow is taken as 0.7. Substituting this into Equations 2 and 3 in Example 5, the upstream dam slope α of the dam was obtained. u The slope α of the upstream dam of the landslide dam is 15°. d The angle is 10.5°. Perpendicular to the main river channel at a 20° angle, the longitudinal sedimentation gradient i of the debris flow dam is generally taken as 0.5 times the longitudinal gradient of the debris flow channel (164‰), which is 8.20%.

[0146] Then, the total volume V of the dammed river is obtained by using the segmented accumulation method described in Examples 4 and 5, corresponding to the total height H and total length L of the dammed river. In this example, the dammed river is cut into multiple cross-sections perpendicular to the debris flow channel 100 at ΔL = 20m, resulting in eight cross-sections: cross-section 1-1, cross-section 2-2, cross-section 3-3, cross-section 4-4, cross-section 5-5, cross-section 6-6, cross-section 7-7, and cross-section 8-8. Based on field measurement data, assuming different dammed river heights, when the dammed river height is 6.9m, the calculated total volume V is exactly equal to the total debris flow volume V at the design frequency. c Then, the intersections of the upstream and downstream slope lines of each trapezoidal section of the landslide dam with the ground surface are: 1, 2 u 2 d 3 u 3 d 4 u 4 d 5 u 5 d 6 u 6 d 7 u 7 d 8 u 8 d The areas formed by the smooth, sequential connection of the debris flow dam are the accumulation range of the dammed debris flow blocking the river.

[0147] The calculation parameters for the cross-sectional area of ​​each cross section are shown in Table 3:

[0148] Table 3

[0149] The segmental volume between each cross-section in Table 3 is 6445 m³. 3 8300m 3 8765m 3 4890m 3 2928m 3 1470m3 608m 3 52m 3 The total volume of the entire landslide dam is 3.34 x 10⁴ m³. 3 .

[0150] Based on the predicted deposition range of the debris flow dam, the length of the dammed body deposited in the main river channel within a 200-meter radius is measured to be 110m, i.e., L = 110m. This determines the lengths of the roughening construction required in the first region Q1 and the second region.

[0151] Of course, the method described in Example 3 can also be used to obtain the correspondence between the total volume V of the river dam and the total height H and total length L of the river dam, thereby obtaining the predicted total length L of the river dam under the target working condition. Further details will not be elaborated here.

[0152] The water levels during the dry and wet seasons at 200 cross-sections of the main channel were calculated using Manning's formula in the hydraulic calculation manual. When calculating the water level during the dry season, a flow rate of 50 m³ / h was used. 3 / s, when calculating the water level during the high-water season, the flow rate used is the high-water season flow rate of 180m³. 3 / s, In actual calculations, different riverbed sections are cut along the river channel direction according to the accuracy requirements, and calculations are performed according to the Manning formula, as shown in Figure 5. In this embodiment, a section is cut at 20m intervals along the river channel direction for calculation, and the results are shown in Table 4:

[0153] Table 4

[0154] Note: The elevation of the riverbed was obtained through on-site measurement, and the water levels during the dry and wet seasons were calculated using the Manning formula.

[0155] Furthermore, in this embodiment, the width of the main river is 35m, which is a large river. Therefore, the target roughness n1 of the first region Q1 is 0.026, the target roughness n2 of the second region is 0.015, and the target roughness n3 of the third region is 0.033; which is significantly less than 0.045 before roughness reduction was implemented.

[0156] Construction was carried out in the roughness reduction area during the dry season, with the target roughness rate of each area serving as an important acceptance indicator. After the roughness reduction construction was completed, the hydrodynamic conditions of the main river were improved, the obstruction of the river boundary to the landslide dam was reduced, and the length of the landslide dam along the river direction was increased, thereby achieving the goal of reducing the height of the opposite bank dam and the capacity of the landslide dam lake.

[0157] The other parts of this embodiment are the same as any one of Embodiments 1-5, so they will not be described again.

[0158] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications or equivalent changes made to the above embodiments based on the technical essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for reducing the danger of debris flows blocking rivers and creating barrier lakes, characterized in that, First, predict the accumulation range of the blockage body blocking the river when the debris flow occurs, and divide the river into multiple areas according to the elevation of the river boundary. Then, during the dry season, carry out roughening treatment on the river boundary in different areas.

2. The method for reducing the danger of debris flow blocking rivers and creating barrier lakes according to claim 1, characterized in that, The division of multiple regions according to the elevation of the river boundary refers to the following: within the accumulation range of the dammed river, the river boundary is divided into three sub-regions from low to high according to the water level during the dry season and the water level during the wet season: the first region with an elevation lower than the water level during the dry season, the second region with an elevation higher than the water level during the dry season but lower than the water level during the wet season, and the third region with an elevation higher than the water level during the wet season. The target roughness of the three sub-regions are denoted as n1, n2, and n3, respectively, and satisfy the following: The target roughness of the second region n2 < the target roughness of the first region n1 ≤ the target roughness of the third region n3.

3. The method for reducing the danger of debris flow blocking rivers and creating barrier lakes according to claim 2, characterized in that, The target roughness n1 of the first region is selected with reference to the roughness of natural river channels, specifically for clean, straight rivers without shallows or deep pools in plains.

4. The method for reducing the danger of debris flow blocking rivers and dammed lakes according to claim 2, characterized in that, The target roughness n2 of the second region is selected with reference to the roughness of the artificial channel.

5. The method for reducing the danger of debris flow blocking rivers and dammed lakes according to claim 2, characterized in that, The target roughness n3 of the third region was selected with reference to the hydraulic calculation manual and the engineering survey specifications for debris flow disaster prevention and control.

6. A method for reducing the danger of debris flow blocking rivers and dammed lakes according to claim 2, 3, or 5, characterized in that, When performing roughening treatment on the first area or the third area, obstacles that hinder water flow are removed, and rough areas are smoothed by excavation and filling.

7. A method for reducing the danger of debris flow blocking rivers and dammed lakes according to claim 2 or 4, characterized in that, When performing roughening treatment on the second area, firstly, obstacles that hinder water flow are removed, then the areas with abrupt changes in terrain are leveled by excavation and filling, and finally, concrete is used to solidify the area, forming a smooth concrete revetment at the river boundary of the second area.

8. The method for reducing the danger of debris flow blocking rivers and dammed lakes according to claim 1, characterized in that, Before predicting the extent of debris flow blockage in the river channel, the debris flow blockage coefficient C is first calculated at the design frequency based on the debris flow blockage discrimination formula. r Used to determine the debris flow blocking river pattern; when C r If the value is greater than 1.44, it can be concluded that a mudslide will block the river.

9. The method for reducing the danger of debris flow blocking rivers and creating barrier lakes according to claim 1, characterized in that, When predicting the deposition range of a river dam during a debris flow: Using 3D design software, a dam model is first generated based on the topographic data, including the DEM of the debris flow channel and the main river channel. This model simulates the 3D structure of the dam at the confluence of the debris flow channel and the main river channel. The 3D structure of this dam includes an upstream dam, a middle main dam, and a downstream dam. The slope of the top of the middle main dam, sloping from the same bank of the debris flow channel to the opposite bank, is denoted as α. i The slope formed by the top of the upstream dam extending from the middle main dam body upstream of the main river is denoted as α. u The slope formed by the top of the downstream dam extending from the central main dam body downstream of the main river is denoted as α. d Then, the key structural parameters in the three-dimensional structure of the dammed river are set: the top width B of the intermediate main dam body and the top slope α of the intermediate main dam body are set. i The upstream slope α of the blockage dam body u The downstream slope α of the landslide dam is... d The morphological characteristics of the gully are known quantities with definite values, thus obtaining a set of variables X that vary with the total volume V of the dammed river. These variables X consist of the total height H and the total length L of the dammed river. Finally, the total volume Vc of the primary debris flow at the predicted design frequency is obtained. Under the constraint that "the total volume V of the dammed river is equal to the total volume Vc of the primary debris flow at the design frequency", a set of corresponding total height H and total length L of the dammed river are solved. Combined with the DEM of the debris flow gully and the DEM of the main river channel, the predicted deposition range of the dammed river in the river channel is obtained.

10. A method for reducing the danger of debris flow blocking rivers and dammed lakes according to claim 9, characterized in that, The morphological features of the gullies were extracted from the DEM of debris flow gullies and the DEM of the main river channel. The top width B of the intermediate main dam body is also the top width of the dam of the river-blocking dam body, which is equal to the width b of the outlet of the debris flow channel, i.e., B = b. The top slope α of the intermediate main dam body i The value is taken according to the longitudinal sedimentation gradient i of the dammed river body, which is j times the longitudinal gradient γ of the debris flow channel, i.e., α i =i=γ*j, j∈(0.5,0.8); The upstream slope α of the blockage dam is... u The angle of repose β of the mudflow is equal to that of the natural mudflow, i.e., α u =β; The downstream slope α of the blockage dam is... d , satisfying: α d =k*α u =k*β, k∈(0,1); where k is the slope reduction coefficient of the downstream slope of the dam under the action of the main river flow; The height H of the opposite bank dam of the intermediate main dam body D The dam height H on the same bank as the intermediate main dam body S Satisfy: H S =(1+α) i )*H D And H S ≤hs、H D ≤h D Where hs is the same-bank elevation of the main river channel, h D The elevation of the opposite bank of the main river channel.

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