A physical simulation method for the impact of silt dam layout on rainstorm and flash flood processes in small watersheds

Abstract

The present invention belongs to the technical field of soil and water conservation, and relates to a physical simulation method for the impact of the layout of silt dams on rainstorm and flash flood processes in small watersheds. The method comprises: a. establishing a small watershed model; b. scanning the small watershed model with a three-dimensional laser terrain scanner to obtain point cloud data of the initial terrain; c. simulating rainfall; collecting sediment samples at the model outlet; d. after the rainfall ends, scanning the small watershed model again with a three-dimensional laser terrain scanner to obtain point cloud data of the terrain after the flash flood; e. calculating the spatial distribution data of soil erosion and deposition in the small watershed; analyzing the hydrodynamic and erosion dynamic characteristics of flash floods in each section of the small watershed; f. changing the layout of the silt dam and repeating the above steps to obtain the spatial distribution data of soil erosion and deposition in the small watershed under different silt dam layouts, and analyzing the hydrodynamic and erosion dynamic characteristics of flash floods in each section. This method provides an effective method for quantitatively analyzing the impact of silt dams on rainstorm and flash floods.

Description

Technical Field

[0001] The present invention belongs to the technical field of soil and water conservation, and in particular relates to a physical simulation method for the impact of silt dam layout on rainstorm and flash flood processes in small watersheds. Background Art

[0002] In recent years, global warming has led to an increase in extreme precipitation events, an increase in the frequency and intensity of rainstorms, and a significant increase in the frequency and risk of rainstorms and flash floods in river basins. This not only seriously affects the normal production and life of people in mountainous areas, hinders social and economic development, but also causes changes in river basins, rivers and soil structures.

[0003] The formation and development of flash floods are influenced by a complex network of factors, including precipitation, topography, soil type, and human activities. These factors interact and influence each other, either promoting or inhibiting their occurrence. Warp dams, as an important soil and water conservation engineering measure, play a significant role in modifying the topography of small watersheds and retaining water and sediment. However, during the evolution of flash floods, some kinetic energy is lost due to the dams' blocking, while some kinetic energy is converted into potential energy, increasing the inundation depth of the floodplain. Therefore, the placement of dams has a significant impact on the development and evolution of flash floods in small watersheds.

[0004] Limited by experimental methods and technical means, current research on torrential rain and flash flood processes is mostly based on numerical simulations of hydrological models. However, there is a lack of scientific methods to guide the identification of the response mechanisms of torrential rain and flash flood processes in small watersheds to the configuration of check dams. Therefore, it is necessary to propose a physical simulation and comparative quantitative method specifically for the flash flood formation and evolution process under different check dam deployment scenarios. This will provide scientific and reliable guidance for revealing the disaster-prone environment and mechanism of torrential rain and flash floods in watersheds, and provide a theoretical basis for scientifically evaluating the effectiveness of check dam measures in controlling flash flood processes. Summary of the Invention

[0005] The purpose of this invention is to provide a practical and effective simulation test method that can capture flash flood processes under conditions without check dams, as well as those under different check dam configurations, such as single dams and multiple dams. This method, which integrates an artificial rainfall simulation system, a small watershed physical model system, and a check dam physical model system, can not only quantitatively analyze the dynamic distribution of flash floods under the influence of check dams and the temporal changes in runoff and sediment production, but also quantify the changes in topographic erosion and sedimentation in small watersheds under the influence of flash floods.

[0006] The present invention provides a physical simulation method for the impact of silt dam layout on rainstorm and flash flood processes in small watersheds, the simulation method comprising the following steps:

[0007] a. Establish a small watershed model:

[0008] Make a small watershed model that meets similarity requirements according to the scale;

[0009] Soil is taken from the prototype site of the field small watershed model, placed in a test trough surrounded by concrete slabs and brick piles, filled and compacted in layers, and the soil bulk density is controlled to be consistent with that of the prototype watershed soil.

[0010] Make a model of small watershed terrain, and carry out trenching, slope cutting, leveling, surface compaction and other treatments on the model according to the scale according to the size, shape, terrain and channel distribution of the prototype small watershed;

[0011] According to the test needs, a silt dam model is laid out at a suitable location for building a silt dam in the small watershed model channel (generally, a dam is built at the mouth of the channel to control the incoming sand of the entire channel. If multiple channels are cascaded, a dam is usually arranged downstream of the intersection of the cascades). The silt dam model is composed of four parts: a dam body, a spillway, a vertical shaft and a stilling basin, in accordance with the actual structure of a large silt dam. The dam body is made of the same soil as the small watershed model, compacted layer by layer, and the dam slope is cut after reaching the design elevation. A spillway is excavated on the side of the dam body with better terrain, the joint is filled with soil, and the spillway is built with concrete. The vertical shaft is spliced ​​with PVC pipes, and a group of 4 drain holes are set every 2.5 cm in the vertical direction of the well wall. The drain holes are 4 cm in diameter and are relatively staggered. A bracket is set above each silt dam;

[0012] At the outlet of the small watershed model, a 2-3 meter open channel is set up and connected to a reservoir. The size of the reservoir is designed according to the rainfall it needs to receive. Generally, its volume should be 1.2-1.5 times the maximum rainfall it can receive.

[0013] An artificial rainfall simulation system is installed above the small watershed model, and the intensity and duration of the rainfall are adjusted through a computer control system to simulate heavy rain processes under different circumstances; positioning balls are placed around the small watershed model, and a three-dimensional laser terrain scanner is set up on the artificial rainfall simulation system directly above the model to quantitatively observe terrain changes; usually, three positioning balls are sufficient, and the more positioning balls there are, the more accurate the positioning.

[0014] The artificial rainfall simulation system consists of a control system, pressure pipes, and downward-spraying simulated raindrops. A 3D laser terrain scanner is mounted on the pressure pipes directly above the model. Each set of raindrops is equipped with five nozzles of varying apertures. The control system adjusts the nozzles and pipe pressure to adjust the rainfall intensity, resulting in simulated rainfall intensities ranging from 30 to 240 mm / h, meeting the raindrop size requirements for rainfall tests. The system, with a rainfall height of 22 meters, ensures that raindrops fall at a uniform rate near the ground, achieving a rainfall uniformity of >85%, meeting the requirements for simulating natural rainfall.

[0015] Determine the sections used to detect the water flow parameters of each channel and the water flow parameter measurement position after the channel water flow is aggregated. Specifically, the sections are set at the outlet position of a single channel, the midstream position after the channel is aggregated, and the model outlet position.

[0016] b. Before rainfall begins, use a 3D laser terrain scanner to scan the small watershed model and the surrounding positioning spheres to obtain point cloud data of the initial terrain.

[0017] The present invention uses a three-dimensional laser scanner to adopt a target-based data acquisition method to obtain small watershed terrain point cloud data. Each scan requires the deployment of measuring stations and positioning balls. The scanning resolution is 1 / 4 (that is, the scanner obtains 240,000 laser points per second), the scanning quality is 4× (that is, the instrument repeats the scan at the station 4 times), and the number of point clouds obtained is about 100 million.

[0018] c. Simulate rainfall and measure the rainfall at the top of the slope and the ditch of the small watershed 30 minutes after the rainfall to calibrate the rainfall intensity and uniformity;

[0019] During rainfall, sediment samples were collected from the reservoir at the model outlet. Data on hydrodynamic and erosion dynamic characteristic parameters were measured, such as the water depth and width in front of the dam after siltation occurred, the water depth and width at the cross section after flow generation in the shaft, the channel runoff velocity and average surface velocity, and the average runoff depth and water temperature at the cross section.

[0020] d. After the rainfall ends, the small watershed model and the surrounding positioning balls are scanned again with a three-dimensional laser terrain scanner to obtain the terrain point cloud data after the flash flood.

[0021] e. After the test, the point cloud data obtained by the 3D laser scanner were spliced, denoised, and registered to obtain a point cloud digital model with a point spacing of 2 mm. The pre-rainfall terrain raster data was then subtracted from the rainfall using a raster calculation machine to obtain the spatial distribution data of soil erosion and deposition in the small watershed.

[0022] The volume and mass of the collected sediment samples, as well as the mass of the dried soil samples, are measured to calculate the mountain torrent runoff volume at the model outlet, the real-time runoff sediment content, and other mountain torrent hydrodynamic and erosion dynamic parameters.

[0023] f. Repair and desilt the small watershed model according to the original model drawings. Then, vary the number and location of check dams and repeat the above steps to conduct another test. This will yield data on the spatial distribution of flash flood runoff, flash flood processes, and soil erosion and deposition in the small watershed under different check dam configurations. Analyze the hydrodynamic and erosion dynamics of flash floods at various sections of the small watershed.

[0024] In order to improve the degree of automation of the present invention, in step a, a high-speed camera can be installed on a bracket above the silt dam model and connected to a computer, and the distribution of mountain torrent runoff before and after the silt dam can be collected by software on the computer; overflow weirs ( Figure 1 (not shown) and install flow monitoring sensors to automatically monitor the changes in the runoff volume and sediment content of mountain torrents in each channel; install an automatic runoff and sediment monitoring system at the connection between the model outlet and the open channel to monitor the changes in the total runoff volume and sediment content of mountain torrents in the small watershed;

[0025] In step c, during rainfall, a high-speed camera is used to capture the mountain torrent flow field near a silt dam every 30 seconds; a flow monitoring sensor is used to measure the mountain torrent runoff and sediment content of each channel in real time; and an automatic runoff and sediment monitoring system is used to monitor the total runoff and sediment content of the mountain torrents at the outlet of the small watershed in real time every 2 minutes.

[0026] The beneficial effects of the present invention are:

[0027] 1. The technical solution of the present invention forms a flash flood process simulation method that integrates "small watershed silt dam layout - fine simulation of flash flood process - flash flood process parameter acquisition - terrain evolution process extraction", and realizes the comparative observation of small watershed flash flood process under different silt dam layout scenarios, providing an effective method for quantitative analysis of the impact of silt dams on rainstorm flash floods.

[0028] 2. The technical solution of the present invention can simultaneously collect the runoff fields before and after the silt dam, the mountain torrent runoff volume and sediment content changes in each channel, and the changes in the small watershed topography under the influence of rainstorms and mountain torrents.

[0029] 3. The present invention uses a three-dimensional laser scanner to scan the terrain and obtains small watershed terrain raster data with a resolution of 2mm, which is far beyond the accuracy of traditional total stations and GPS-RTK terrain measurements.

[0030] 4. Existing rainfall erosion research is limited by experimental soil troughs and terrain observation methods. Most of them can only analyze erosion phenomena, and it is difficult to analyze or record deposition phenomena. The present invention can well present all erosion and deposition phenomena. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a small watershed model diagram of an embodiment of the present invention;

[0032] Figure 2 4 is a diagram of a silt dam model according to an embodiment of the present invention.

[0033] Figure 3 This is a characteristic diagram of the changes in runoff and sediment yield rates due to rainstorms and flash floods under different silt dam layout scenarios in small watersheds.

[0034] Figure 4 This is the spatial distribution map of soil erosion and deposition in a small watershed under different silt dam layout scenarios (Note: the scales on the lower and left borders represent the horizontal and vertical coordinates).

[0035] Figure 5 This is a characteristic diagram of the changes in the runoff and sediment yield rates of rainstorm flash floods under different rainfall intensities in a small watershed.

[0036] Figure 6 This is the spatial distribution map of soil erosion-deposition in a small watershed on bare land under different rainfall intensities (Note: the scales on the lower and left borders represent the horizontal and vertical coordinates).

[0037] Figure 7 This is the spatial distribution map of soil erosion and deposition in a small watershed under different rainfall intensities (Note: the scales on the lower and left borders represent the horizontal and vertical coordinates).

[0038] Figure 8 This is a diagram of the erosion-deposition ratio at each level in the small watershed under different test conditions.

[0039] Figure 9 This is the time-course distribution diagram of erosion and sediment transport rate in sections B and C of the small watershed under different silt dam configuration scenarios.

[0040] Figure 10 This is a characteristic diagram of the average flow velocity changes in sections B and C of the small watershed under different silt dam configuration scenarios.

[0041] Figure 11 This is the Re variation characteristic diagram of sections B and C in the small watershed under different silt dam configuration scenarios.

[0042] Figure 12 This is the characteristic diagram of Fr changes in sections B and C of the small watershed under different silt dam configuration scenarios.

[0043] Figure 13 This is a characteristic diagram of the change of f in sections B and C of the small watershed under different silt dam configuration scenarios.

[0044] Figure 14 Variation characteristics of ω in sections B and C of the small watershed under different silt dam configuration scenarios.

[0045] Figure 15 This is a characteristic diagram of the changes in sections E of the small watershed B and C under different silt dam configuration scenarios.

[0046] In the figure: 1. Working platform; 2. Brick stack; 3. Precast concrete slab; 4. Dam No. 1; 5. Dam No. 2; 6. Flow monitoring sensor; 7. Main ditch silt dam; 8. Stairs; 9. Automatic runoff and sediment monitoring system; 10. Computer; 11. Open channel; 12. Reservoir; 13. High-speed camera; 14. Bracket; 15. Vertical shaft; 16. Discharge hole; 17. Spillway; 18. Stilling basin; 04. Channel No. 1; 05. Channel No. 2; 07. Channel No. 3. DETAILED DESCRIPTION

[0047] The present invention is described in more detail below through specific implementation methods to facilitate understanding of the technical solution of the present invention, but is not intended to limit the scope of protection of the present invention.

[0048] Example 1

[0049] A physical simulation method for the impact of silt dam layout on rainstorm and flash flood processes in a small watershed includes the following steps:

[0050] (1) Establish a small watershed model:

[0051] The small watershed model is based on the Qiaogou small watershed, a first-level tributary of the Wuding River in the loess hilly gully area, with a horizontal and vertical scale of 1:40. The model is 31.5m long, 16.5m wide and 3.3m high. Figure 1 The soil used for the model was taken from the surface loess near the bridge ditch and filled in layers into a rectangular test trough surrounded by precast concrete slabs 3 and brick stacks 2. The soil was compacted and the dry bulk density was controlled to be between 1.42 and 1.45 g / cm 3 , which is equivalent to the soil bulk density of the basin under natural conditions.

[0052] Based on the prototype of the Qiaogou small watershed terrain, a model terrain was made according to the scale. After digging ditches, cutting slopes, leveling, and surface compaction, the channel distribution, shape, undulation, and gully density were controlled to be similar to the actual watershed. Specifically, the small watershed terrain has Channel 1 04, Channel 2 05, and Channel 3 07. Figure 1 As shown;

[0053] Combined with the field investigation, a silt dam No. 1 Dam 4, No. 2 Dam 5 and main ditch silt dam 7 were respectively built in the model's channel No. 1 04, channel No. 2 05 and channel No. 3 07.

[0054] The check dam model was designed based on the actual structure of a large check dam and consists of four parts: the dam body, spillway 17, vertical shaft 15, and stilling basin 18. The dam body was constructed using the same loess as the Qiaogou small watershed, compacted in layers of 10 cm each. After reaching the design elevation, the dam slope was cut with a side slope ratio of 1:2. Due to the short rainfall duration of the test, the effects of seepage were not considered.

[0055] Table 1 Warping dam design

[0056]

[0057] Spillway Design: During spillway construction, a deep channel was excavated on the side of the dam with better terrain, and the interface was filled with soil. The spillway was constructed using C25 concrete with a side slope ratio of 1:2, a bottom width of 10 cm, and a depth of 20 cm. To reduce the risk of seepage at the interface between the concrete and the dam body, the concrete side slope was extended a certain distance toward the dam body. A stilling basin was constructed at the spillway outlet to reduce erosion of the channel by overflow water.

[0058] Shaft design: Made of PVC pipes, the shaft has an inner diameter of 0.02 cm and an outlet diameter of 4 cm. A group of four drain holes 16 are set every 2.5 cm along the vertical direction of the shaft wall, and the drain holes are relatively staggered.

[0059] Five fixed positions (sections A, B, C, D, and E) were selected as the measurement positions of the experimental parameters, among which sections A, D, and E were located at the outlets of channels No. 1, 2, and 3, and the changes in water flow parameters in channels No. 1, 2, and 3 could be observed; section B was located in the middle reaches of channel No. 1, and the changes in water flow parameters after the water flows in channels No. 1 and 2 were combined could be observed; section C was located at the total outlet of the model downstream of No. 1, and the changes in water flow parameters after the water flows in channels No. 1, 2, and 3 were combined could be observed.

[0060] A 3-meter open channel 11 is set at the outlet of the small watershed model and connected to a reservoir 12. The size of the reservoir is designed according to the rainfall to be received. Generally, its volume should be 1.2 to 1.5 times the maximum rainfall it can receive. The reservoir of this embodiment has a length * width * depth = 2 meters * 3 meters * 1.5 meters.

[0061] A downspout rainer (TSJY-1, manufactured by Nanjing Tusheng Data Engineering Co., Ltd.) was installed above the model. A 3D laser terrain scanner (FARO FOCUS 3D) was mounted on the pressure pipe directly above the model. Six positioning balls were evenly spaced around the model. The 3D laser terrain scanner was connected to a computer 10 via a network cable.

[0062] like Figure 1 As shown, a working platform 1 is provided at the upper left corner of the rectangular test tank, and stairs 8 are provided at the lower left and lower right of the test tank to facilitate staff to go up and down the test tank for observation.

[0063] (2) Before rainfall begins, the soil bulk density and water content of the small watershed are first measured using the ring knife method. The 3D laser terrain scanner is turned on to scan the small watershed model and the surrounding positioning spheres to obtain point cloud data of the initial terrain before rainfall. The scanning resolution is 1 / 4 (i.e., the scanner obtains 240,000 laser points per second) and the scanning quality is 4× (i.e., the instrument repeats the scan at the station 4 times). Each terrain scan requires 7 measurement stations to be evenly distributed around the small watershed, and the number of point clouds obtained is about 100 million. In this embodiment, 7 measurement stations are set because the model of this embodiment is relatively large and the terrain is complex. There will be blind spots during scanning. The measurement station (i.e., the position of the scanner) needs to be changed to ensure that all areas can be covered to avoid blind spots and dead angles.

[0064] Take 6 rain gauges and place them evenly on the top of the slope and in the channel of the basin.

[0065] (3) Then the model was subjected to rainfall simulation at rainfall intensities of 30, 60, and 120 mm / h, with a rainfall duration of 1 h;

[0066] After the rainfall begins, the flow generation time of each channel is recorded.

[0067] Measure the rainfall in the rain gauge 30 minutes after rainfall, and calculate the average value of multiple rain gauges to calibrate the rainfall intensity and uniformity.

[0068] After siltation formed in front of the dam, the water depth and width in front of the dam were measured every 5 minutes with a ruler. After the vertical shaft began to generate flow, the water depth and width were measured every 5 minutes at sections A, B, C, D, and E. The five locations were used as the endpoints, and 1 meter was measured forward as the starting point. The channel runoff velocity was measured using a dye tracer method (KMnO4). Dye was added when the water flow passed the starting point, and the time it took for the dye to reach the endpoint was recorded using a stopwatch to obtain the average surface velocity of the water flow. All runoff sediment samples were collected through the small watershed outlet trough. Each sampling lasted 15 seconds. The sediment sampling container was a 10-liter metal bucket, and the sampling interval was 2 minutes.

[0069] Determine the average runoff depth and water temperature of the section.

[0070] (4) After the rainfall ends and there is no obvious water accumulation on the surface, the 3D laser terrain scanner is turned on again to scan the small watershed model and the surrounding positioning balls to obtain the final point cloud data of the eroded terrain;

[0071] (5) The original point cloud data obtained by the scanner was imported into Trimble Real Works 11.3 software. The point cloud data of each survey station was spliced, denoised, and registered to ensure that the point cloud data before and after the rainfall were in the same spatial coordinate system. Due to the limitation of computer computing power, the point cloud data needed to be thinned. Finally, a point cloud digital model with a point spacing of 2mm was obtained and exported as a .las point cloud format file. A LAS dataset was created in ArcGIS, and then the obtained .las point cloud file was imported into ArcGIS. Using the raster conversion tool, the terrain raster data before and after the rainfall in the small watershed can be obtained. Then, by using the raster calculation machine, the terrain raster data before the rainfall was subtracted from the rainfall to obtain the spatial distribution data of soil erosion and deposition in the small watershed. A positive value indicates that the elevation value of the point before the rainfall was greater than that after the rainfall, indicating that erosion occurred; a negative value indicates that the elevation value of the point before the rainfall was less than that after the rainfall, indicating that deposition occurred. Using the 3D analysis surface volume tool, the erosion and deposition amount in each area can be quantified. Finally, the reclassification tool of ArcGIS was used to perform hierarchical statistics on the obtained raster data of the spatial distribution of erosion and deposition in the small watershed, which was used to calculate the proportion of erosion and deposition at each level in the small watershed and obtain the terrain change situation.

[0072] During each rainfall test, 30 runoff and sediment samples were collected using real-time runoff sampling. Parameters such as the volume and mass of the collected sediment samples, as well as the mass of the metal bucket and the mass of the dried soil sample, were measured. Runoff rate curves were plotted by measuring the volume of the water-sand mixture within the metal bucket. The mass of the sediment within the bucket was determined using a drying method, and a sediment production rate curve was plotted. Finally, these rate curves were integrated to determine the total runoff and sediment volume generated by the small watershed in the experiment. This allowed us to understand the temporal changes in runoff, sediment yield, and sediment content during rainstorms and flash floods in the small watershed. It should be noted that runoff and sediment content represent the changes in runoff and sediment during each statistical period (for example, every minute), while total runoff and sediment content refer to the total amount generated during a single rainfall event. Sediment content is the mass of dry sediment contained in a unit volume of muddy water, while runoff is the volume of water.

[0073] (6) Repair and desilt the small watershed model according to the original model drawings, remove Dam I, retain Dam II, and repeat the above steps to conduct rainfall tests again;

[0074] (7) The small watershed model was repaired and desilted again according to the original model drawings. Dam No. II was removed, and only Dam No. I was retained. The above steps were repeated to conduct the rainfall test again. When different silt dams were set, the rainfall intensity settings were as shown in Table 2:

[0075] (8) Finally, the small watershed model was repaired and desilted according to the original model drawings, all silt dams were removed, and the above steps were repeated to conduct rainfall tests;

[0076] (9) The distribution of mountain torrent runoff in small watersheds under three conditions, namely, double dams (Dam I and Dam II), single dam, and no dam, the spatial distribution and variation data of mountain torrent processes and soil erosion-sedimentation, and the hydrodynamic and erosion dynamic characteristics of mountain torrents at each section were obtained. Through comparative analysis, the impact of the layout of silt dams on the rainstorm mountain torrent process in small watersheds was obtained.

[0077] The impact of silt dam layout on rainstorm and flash flood processes in small watersheds is as follows:

[0078] 1. Response of small watershed flash floods to the placement of silt dams

[0079] 1.1 Process of runoff and sediment generation by rainstorm and flash flood erosion under different silt dam layout scenarios

[0080] In order to effectively identify the response of small watershed flash floods to the placement of silt dams, the number of silt dams was changed under the same rainfall intensity of 60 mm / h. From the analysis of the runoff and sediment production process in the small watershed, it was found that the sediment production rate and the runoff production rate were in the same trend of change. As the runoff production rate increased, the sediment production rate also increased. Figure 3 As shown in the figure, the difference in the number of check dams is significant in terms of runoff generation: the average and peak runoff rates of the single-dam small watershed are 159.563 cm 3 / s、300.436cm 3 / s, and the average and peak values ​​of runoff rate in Shuangba small watershed were 125.302 cm 3 / s、241.591cm 3 / s, with the runoff rate in small watersheds with a single dam being slightly higher than that in small watersheds with two dams. Regarding sediment yield, the average and peak sediment yield rates in small watersheds with a single dam were 4.086g / s and 15.181g / s, respectively, while those in small watersheds with two dams were 1.233g / s and 3.493g / s, respectively. This represents a sediment yield rate roughly four times higher in small watersheds with a single dam than in those with two dams. This suggests that increasing the number of check dams has a minimal impact on runoff in small watersheds, but significantly limits sediment yield.

[0081] 1.2 Spatial distribution of soil erosion and deposition in small watersheds under different check dam layout scenarios

[0082] like Figure 4 As shown in the figure, the spatial distribution of soil erosion and deposition in the small watershed under different check dam layout scenarios with the same rainfall intensity of 60 mm / h shows that after the check dams No. 1 and No. 2 were installed, obvious deposition occurred in the stilling land behind the dams, with the deposition volumes being 2.57*10 4 cm 3 and 6.06*10 4 cm 3This demonstrates that the check dam effectively intercepts sediment carried by runoff in front of the dam. Furthermore, by the time the runoff, intercepted by the check dam, exits the spillway and shaft, its flow rate and velocity have stabilized, significantly reducing its erosion potential in the channel behind the dam. Therefore, the placement of the check dam not only intercepts sediment carried by upstream runoff, but also reduces the intensity of erosion and sedimentation in the downstream channel.

[0083] 2. Response of small watershed flash flood processes to rainstorm intensity

[0084] 2.1 Rainstorm and flash flood erosion and sediment production process under different rainfall intensities

[0085] In order to effectively identify the response of small watershed rainstorm and flash flood processes to rainfall intensity, the runoff and sediment production processes of small watersheds under different rainfall intensities were analyzed by changing the rainfall intensity under the same engineering measures. The working condition settings are shown in Table 2:

[0086] Table 2 Rainfall intensity settings under different silt dam settings

[0087]

[0088] like Figure 5 As shown in the figure, when the rainfall intensity is 60 mm / h, the runoff and sediment yield rates of the small watershed maintain a slowly rising trend in the early stage, but at 35 minutes, the runoff and sediment yield rates suddenly increase rapidly. This is because the water level in the silt dam has reached the position of the spillway at this time, and the spillway begins to discharge water. The runoff rate of the small watershed quickly increases from 83.364 cm 3 / s increased to 212.928cm 3 / s, significantly enhancing the runoff's scouring and sediment-carrying capacity, and increasing the sediment production rate from 0.427g / s to 2.273g / s. The discharge from the check dam's spillway accounts for over 60% of the total runoff, indicating that erosion conditions in the small watershed are significantly correlated with the dam's storage capacity. At rainfall intensities of 120mm / h, the check dam's reservoir quickly filled due to the heavy rainfall. Furthermore, the discharge from the check dam's spillway in this test had little impact on the total runoff. Therefore, although the runoff and sediment production rates in this test small watershed fluctuated, they did not undergo a sudden change.

[0089] 2.2 Spatial distribution of soil erosion and deposition in small watersheds under different rainfall intensities

[0090] like Figure 6As shown in the figure, the spatial distribution of soil erosion and deposition in the bare land small watershed under different rainfall intensities of 30 mm / h and 60 mm / h shows that under a rainfall intensity of 30 mm / h, soil erosion mainly occurs on the slope surface, while erosion in the channel is relatively small. This may be because the rainfall intensity is too low to form runoff with scouring capacity in the channel, so only a certain degree of splash erosion occurs on the slope surface. A large area of ​​deposition is formed at channel No. 1 (6, 14) to (6, 22), with a deposition volume of approximately 4.035*10 5 cm 3 This means that under a rainfall intensity of 30 mm / h, although the runoff in the channel is slow and lacks scouring capacity, it can still transport the sediment generated by slope erosion to the gentle slope or low-lying areas of the channel. When the rainfall intensity is 60 mm / h, due to the increase in rainfall intensity, in addition to the splash erosion of the slope, erosion also occurs at the head of Channel No. 2 (12, 12), with an erosion volume of approximately 1.397*10 5 cm 3 This may be because the area has a large rain-bearing surface, where the slope flow converges to form gully head erosion. The runoff carrying a large amount of sediment here produced channel deposition at the gentle slope of the second channel (7, 18) to (8, 15), with a deposition volume of approximately 5.14*10 4 cm 3 At this time, the flow rate and velocity of the runoff in channel No. 1 (6, 14) to (6, 22) are different from those when the rainfall intensity is 30 mm / h. The runoff flow rate and velocity in the channel become stronger, and the sediment carrying capacity of the runoff also increases accordingly. Sedimentation no longer occurs in the channel, but channel erosion occurs instead. The volume of soil loss in the eroded channel is about 3.35*10 4 cm 3 .

[0091] like Figure 7 As shown in the figure, the spatial distribution of soil erosion and deposition in the small watershed of Danba under different rainfall intensities of 60 and 120 mm / h shows that when the rainfall intensity is 120 mm / h, the intensity of erosion and deposition in the entire small watershed increases significantly, and erosion gullies are formed at (8, 28) to (10, 22) in channel No. 3. This is because channel No. 3 with a smaller catchment area also forms a certain scale of runoff under the action of heavy rainfall, and the slope of the channel is steep, and its runoff has strong scouring and sand-carrying capacity. This may be the reason why only erosion but no deposition occurs here.

[0092] 2.3 Comprehensive Analysis

[0093] The ArcGIS reclassification tool was used to perform hierarchical statistics on the spatial distribution of erosion-deposition raster data for all experiments. For the convenience of description, this example defines the erosion-deposition intensities (0-10), (10-50), (50-150), and (150-300) mm as mild, moderate, severe, and serious erosion-deposition, respectively. Figure 8 It can be found that under the action of rainfall intensity of 60mm / h, the proportion of severe and serious erosion in the small watershed is significantly reduced by increasing the number of silt dams, that is, the intensity of gully erosion in the small watershed is reduced with the increase of silt dams, which is consistent with the Figure 4 The spatial distribution of erosion and sedimentation in small watersheds under different engineering measures corresponds to each other. Under the same silt dam measures in small watersheds, as the rainfall intensity increases, the proportion of moderate, severe and serious erosion and sedimentation increases significantly, which means that more drastic topographic changes and sediment transport occur, which is consistent with the Figure 6 、 Figure 7 The spatial distribution of erosion and sedimentation corresponds to the erosion and sedimentation distribution map. Finally, combined with Statistical Table 3, we find that the total runoff under the experimental condition of "double dams at 120 mm / h" was 5.93 times that of the "single dam at 60 mm / h," and the total sediment loss was 33.73 times that of the "single dam at 60 mm / h." The total runoff under the experimental condition of "single dam at 60 mm / h" was 1.26 times that of the "double dam at 60 mm / h," and the total sediment loss was 3.23 times that of the "double dam at 60 mm / h." This shows that soil and water conservation measures have a significant flood and sediment reduction effect for low to medium rainfall intensity, but their effectiveness is reduced for high-intensity rainstorms and floods.

[0094] Table 3 Runoff and sediment yield in small watersheds under different test conditions

[0095] Test conditions Rainfall intensity (mm / h) Total runoff (L) Total amount of sediment loss (g) Single Dam 60 563.25 13.78 Shuangba 60 444.84 5.26 Shuangba 120 3345.62 464.82

[0096] From the above, we can conclude that: (1) in a small watershed, soil erosion can occur both on the slope and in the gully under the influence of rainstorms and mountain torrents, but deposition usually only occurs in the gully.

[0097] (2) The intensity of slope erosion in a small watershed is positively correlated with rainfall intensity. The greater the rainfall intensity, the deeper the slope erosion. When the rainfall intensity is 120 mm / h, the flow rate in the channel is large, the channel is prone to erosion and sedimentation is less. Conversely, when the rainfall intensity is 30 and 60 mm / h, sedimentation is obvious in the channel, but erosion is less.

[0098] (3) Warping dams are effective in intercepting sediment carried by runoff in channels. They can effectively intercept sediment carried by runoff in front of the dam. At the same time, silt dams can also regulate the runoff volume behind the dam, thereby reducing the intensity of erosion in the channel behind the dam to a certain extent. The deployment of silt dams can effectively reduce soil loss during rainstorms and mountain torrents, and play a role in water storage and soil conservation.

[0099] (4) Under low to moderate rainfall intensities (30-60 mm / h), the erosion depth and sediment thickness of small watersheds are mainly concentrated within 10 mm. However, under high rainfall intensities of 120 mm / h, the proportion of soil erosion and sedimentation will double regardless of whether the small watershed has a check dam. Soil and water conservation measures have a good flood and sediment reduction effect for low to moderate rainfall, but their flood and sediment reduction effect will be reduced for high-intensity rainstorms.

[0100] 3. Characteristics of Flash Flood Processes

[0101] The temporal distribution characteristics of runoff and sediment transport rate can clearly reflect the impact of different silt dam layout conditions on the flash flood process in small watersheds. Figure 9 As shown in the figure, the temporal distribution of erosion and sediment transport rates in sections B and C of the small watershed under different check dam configuration scenarios shows that the runoff and sediment transport rate increase over time under different check dam configuration conditions. The runoff and sediment transport rate in the no-dam scenario are much greater than those in the other three check dam configuration scenarios. The runoff decreases most significantly in the double-dam scenario. Within 60 minutes, the maximum increase in erosion in the no-dam scenario exceeds 114.60 g / s, while the maximum increase in runoff in the double-dam scenario is only 70.11 g / s. The sediment transport rate in section B under scenarios No. 1 single dam, No. 2 single dam, and double dams decreases by 3.76%, 1.71%, and 11.39%, respectively, compared with the no-check dam scenario. The sediment transport rate in section C decreases by 13.70%, 13.99%, and 18.52%, respectively, compared with the no-check dam scenario.

[0102] 4. Dynamic characteristics of mountain torrents

[0103] 4.1 Flow velocity variation characteristics

[0104] During flash floods, the average runoff velocity across channel cross-sections fluctuates over time. The average velocity is lowest at the beginning of rainfall, then slowly increases and stabilizes over time. This velocity fluctuation is primarily due to both flow velocity and channel morphology. During rainfall, runoff erodes channels, increasing the depth and width of rills within them. This influences the flow velocity within these rills, which in turn further alters rill morphology. These two factors interact and influence each other.

[0105] The average flow velocity of Section B shows a trend of first increasing and then stabilizing under the four scenarios. The average flow velocity is the largest in the no-dam scenario, with an average value of 0.32 m / s, and the smallest in the double-dam scenario, with an average value of 0.23 m / s. The average flow velocity of Section C is generally greater than the average flow velocity of Section B. Under different silt dam layout scenarios, the average flow velocity of Section B in the no-dam, No. Ⅰ single dam, and No. Ⅱ single dam scenarios are 1.32 to 1.87 times, 0.73 to 1.28 times, and 1.00 to 1.70 times the average flow velocity of Section B in the double-dam scenario, respectively; the average flow velocity of Section C is 1.05 to 1.81 times, 0.69 to 1.43 times, and 1.17 to 1.81 times the average flow velocity of Section C in the double-dam scenario. Figure 10 Overall, the single-dam scenario I and the double-dam scenario have a significant impact on the channel flow velocity. In particular, during the 20- to 45-minute rainfall period, the difference between the flow velocity of the single-dam scenario I and the double-dam scenario and the average flow velocity of the no-measure scenario and the single-dam scenario II increases rapidly. The check dam significantly hinders the increase in flow velocity, and the double-dam measure is the most effective. However, the control effect on the channel runoff velocity is relatively small compared to the single-dam measure.

[0106] 4.2 Reynolds number variation characteristics

[0107] The Re variation characteristic curves of sections B and C in the small watershed under different silt dam configuration scenarios are shown as follows: Figure 11 As shown in the figure, the dividing line value Re=500 is added to analyze the state change characteristics of the cross-section runoff at different times.

[0108] As shown in the figure, Re varies from 58 to 1531, with the overall value gradually increasing over time. In the no-dam scenario, runoff at sections B and C remains turbulent, and the degree of turbulence continues to increase. The runoff turbulence in the single-dam scenario II is second only to that in the no-dam scenario. The runoff at sections B and C changes from laminar to turbulent after 10 to 15 minutes. In the single-dam and double-dam scenarios I, the runoff at sections B and C is significantly affected by the placement of the check dam, with the runoff gradually transitioning to turbulent after 50 minutes. Therefore, the comparison of Re values ​​over the same time periods follows the order: no dam > single dam II > single dam I > double dams. This is because the check dam's interception and storage of runoff hinders runoff flow and causes significant sediment deposition. This reduces runoff flow in the underlying channel, slows the rate of flow velocity growth, and reduces scouring of the downstream channel. The placement of the check dam significantly reduces flow velocity variations, slows the rate of Re growth, and slows the onset of turbulent flow patterns.

[0109] 4.3 Variation characteristics of Froude number

[0110] The Fr variation characteristic curves of sections B and C in the small watershed under different silt dam configuration scenarios are as follows: Figure 12 As shown in the figure, the dividing line value Fr=1 is added to analyze the state change characteristics of the cross-section runoff at different times.

[0111] With a few exceptions, the overall Fr value is less than 1, indicating a slow flow in each channel. Fr values ​​for the 35-, 40-, and 50-minute periods at Section B are slightly greater than 1, presumably because the increase in flow velocity during these periods exceeds the increase in water depth, leading to an increase in Fr. The Fr ranges are larger in the no-dam scenario and the single-dam scenario (Scenario I), ranging from 0.37 to 0.96 and 0.45 to 1.30, respectively. The Fr ranges are smaller in the single-dam and dual-dam scenarios (Scenario II), ranging from 0.51 to 0.91 and 0.45 to 0.85, respectively. This suggests that the deployment of check dams can improve the stability of runoff flow, with the stabilization effect being even more pronounced in the dual-dam scenario.

[0112] 4.4 Variation characteristics of drag coefficient

[0113] The characteristic curves of f change in sections B and C of the small watershed under different silt dam configuration scenarios are as follows: Figure 13 shown.

[0114] Under the four check dam scenarios, f at sections B and C is extremely small, fluctuating between 0.004 and 0.022. The main causes of this fluctuation are changes in flow velocity, water depth, and water width. In section B, f shows a fluctuating downward trend, ranging from 0.005 to 0.009. In section C, f is relatively stable, with an overall gentle trend. In the no-dam scenario and single-dam scenario II, f remains stable, fluctuating between 0.007 and 0.013, and 0.007 and 0.010, respectively. Scenario I and the dual-dam scenario are significantly affected by the check dam, with f values ​​generally greater than those of the other two scenarios and more dramatic fluctuations. Check dams reduce cross-sectional runoff velocity and alter the dynamics of runoff flow. Runoff is subject to greater obstruction during flow. As f increases, runoff velocity decreases further, and the sediment-carrying capacity of the runoff gradually weakens.

[0115] 5. Dynamic Characteristics of Mountain Torrent Erosion

[0116] 5.1 Runoff power

[0117] The variation characteristics of ω in sections B and C of the small watershed under different silt dam configuration scenarios are as follows: Figure 14 As shown in the figure, the ω of both sections increases with time. The ω of section B is the largest in the case of no dam, and the minimum ω is 0.023 (N·m -1 ·s -1 ), the maximum value is 0.043 (N·m -1 ·s -1 ), followed by the No. Ⅱ single dam scenario, with a similar trend to the no-dam scenario. The No. Ⅰ single dam and double dam scenarios decreased ω significantly, with a maximum value of 0.023 (N·m -1 ·s -1 ), minimum value 0.004(N·m-1 ·s -1 ), the maximum value is the same as the minimum value in the no-dam scenario. ω in the no-dam scenario is 1.80 to 5.53 times that in the double-dam scenario. In section C, ω in the no-dam scenario is still the largest. The order of ω in other scenarios is the same as that in section B. ω in the no-dam scenario is 1.42 to 2.45 times that in the single-dam scenario No. Ⅰ and 1.59 to 2.64 times that in the double-dam scenario. This shows that the change in the layout scenario of the check dam has a great impact on ω. ω in the no-dam scenario is much greater than that in the dam scenario. The ω curve in the double-dam scenario intersects with that in the single-dam scenario No. Ⅰ. Dam No. Ⅰ plays a dominant role in the runoff flow in the channel, while Dam No. Ⅱ plays a smaller role.

[0118] 5.2 The runoff erosion power can be seen from the change characteristics of sections E of the small watershed B and C under different silt dam configuration scenarios ( Figure 15 ), the runoff erosion power of sections B and C in the no-dam scenario is much greater than that in the dam scenario. In section B, the runoff erosion power of C in the No. Ⅰ single dam scenario and the double dam scenario is relatively small within 0-40 min, with an increase of only 2.62×10 -3 (m 4 ·s -1 km -2 ) and 1.79×10 -3 (m 4 ·s -1 km -2 ), it only increases significantly after 40 to 60 minutes. The changes in C under the No. 1 single dam scenario and the double dam scenario in section C are the same as those in section B. This shows that the layout of the check dam can not only reduce the runoff erosion power, but also greatly delay the growth trend of the runoff erosion power.

[0119] 6. Relationship between Erosion Characteristics and Hydrodynamic and Erosion Dynamic Parameters

[0120] The placement of check dams alters the dynamic distribution characteristics of flash floods in small watersheds. With changes in erosion and sediment transport rates, the formation and development of flash floods during rainstorms are controlled. The patterns of flash flood disasters are analyzed through changes in hydrodynamic and erosion dynamic characteristics. The Pearson correlation coefficient method was used to analyze flash flood dynamic and erosion dynamic parameters, and correlations between sediment transport rates and these parameters were obtained (Table 4).

[0121] Table 4 shows a good correlation between sediment transport rate and most parameters. Because the placement of check dams prolongs the time that channel runoff remains laminar, the water moves in a regular pattern, weakening the influence of viscosity on runoff and thus reducing the force of runoff on erosion and sediment production. Under the four check dam placement scenarios, the average flow velocity and Re (hydrodynamic parameters) and the erosion dynamic parameters ω and E (erosion dynamic parameters) at sections B and C significantly influence channel runoff and sediment production. Among the hydrodynamic parameters, Re has the greatest impact on erosion and sediment production, followed by the average runoff flow velocity. Among the erosion dynamic parameters, ω has a more pronounced effect on channel runoff and sediment production, while E has a relatively smaller effect. A comparison reveals that runoff power, runoff erosion power, Reynolds number, and average flow velocity play the dominant roles in driving flash floods in small watersheds, with the order of dominance being ω > Re > E > V. Overall, the erosion dynamic parameters have a greater impact on channel runoff and sediment production than the hydrodynamic parameters.

[0122] Table 4 Correlation between mountain torrent sediment transport rate and changes in hydrodynamic parameters and erosion dynamic parameters in small watersheds

[0123]

[0124] Note: “*” indicates significant correlation at the 0.05 level (two-sided), and “**” indicates significant correlation at the 0.01 level (two-sided).

[0125] From the above, we can conclude that (1) under the action of heavy rain, the mountain torrent runoff and sediment transport rate of the small watershed in Huangqiu District increased over time. The erosion amount increased the most when no check dam was deployed, exceeding 114.6 g / s. The sediment transport rate under the scenarios of single dam No. Ⅰ, single dam No. Ⅱ, and double dams was reduced by 13.70%, 13.99%, and 18.52% compared with the sediment transport rate under the scenario of no check dam.

[0126] (2) Warping dams have a significant inhibitory effect on the increase in mountain torrent flow velocity. The double dam measure is the most effective, but its effect on the control of channel runoff velocity is limited compared to a single dam. It has a greater impact on the runoff flow state. Under the double dam scenario, the time that the runoff remains in laminar and slow flow is significantly increased. The layout of the warping dam will lead to an increase in the resistance coefficient, thereby affecting the runoff flow and sediment transport capacity.

[0127] (3) Warping dams have a significant impact on the evolution of rainstorm and flash floods in small watersheds. They can not only reduce runoff power and runoff erosion power, but also delay the growth trend of runoff erosion power to a great extent.

[0128] (4) The dynamic parameters that play a dominant role in driving flash floods in small watersheds are runoff power > Reynolds number > runoff erosion power > average flow velocity. The influence of erosion dynamic parameters on flash floods is generally greater than that of hydrodynamic parameters.

[0129] The above results quantitatively reveal the impact of the configuration of silt dam measures on the formation and evolution of rainstorm and flash floods in small watersheds in Huangqiu District, and clarify the disaster-prone environment and disaster mechanism of rainstorm and flash floods in the watershed.

[0130] Example 2

[0131] The experimental steps of this embodiment are basically the same as those of Example 1, except that:

[0132] In step (1), a bracket 14 is set above the silt dam, an MVC3000SAC-GE12 high-speed camera 13 is installed on the bracket, and the camera is connected to a computer 10 via a network cable. An LTW-1 flow monitoring sensor 6 is installed at each channel mouth, and an HL-2 runoff and sediment automatic monitoring system 9 is installed at the connection between the model outlet and the open channel.

[0133] Step (3): During rainfall, a high-speed camera is used to collect the mountain torrent flow field near a silt dam every 30 seconds; a flow monitoring sensor is used to measure the mountain torrent runoff and sediment content of each channel in real time; and an automatic runoff and sediment monitoring system is used to monitor the total runoff and sediment content of the mountain torrent at the outlet of the small watershed in real time every 2 minutes.

[0134] This embodiment uses high-speed cameras to monitor the total runoff and sediment content of mountain torrents at the outlet of a small watershed, and verifies the results with manual measurement.

[0135] The embodiments described above are only preferred embodiments of the present invention and do not limit the scope of implementation of the present invention. Therefore, any equivalent changes or modifications made according to the structure, characteristics and principles described in the patent scope of the present invention should be included in the scope of the patent application of the present invention.

Claims

1. A physical simulation method for the impact of silt dam layout on rainstorm and flash flood processes in small watersheds, characterized by: The following steps are involved: a. Establish a small watershed model: The soil taken from the model prototype site is placed in the test tank and filled and compacted in layers to control the soil bulk density to be consistent with that of the model prototype watershed soil; According to the size, shape, topography and channel distribution of the prototype small watershed, the model is ditched, sloped, leveled and surface compacted according to the scale; Arrange a check dam model in the small watershed model channel, build a dam at the channel mouth to control the sediment inflow of the entire channel. If multiple channels cascade, also place a dam downstream of the cascade intersection; An open channel was set up at the outlet of the small watershed model and connected to a reservoir; an artificial rainfall simulation system was installed above the small watershed model; positioning balls were placed around the small watershed model, and a three-dimensional laser terrain scanner was set up directly above the model; Determine the cross section used to detect the water flow parameters of each channel and the location for measuring the water flow parameters after the channel water flow is aggregated; b. Use a 3D laser terrain scanner to scan the small watershed model and the surrounding positioning sphere to obtain point cloud data of the initial terrain; c. Simulated rainfall: During rainfall, sediment samples were collected from the reservoir at the model outlet, and relevant data on hydrodynamic and erosion dynamic characteristic parameters were measured. d. After the rainfall ends, the small watershed model and the surrounding positioning spheres are scanned again using a 3D laser terrain scanner to obtain point cloud data of the terrain after the flash flood; e. The point cloud data acquired by the 3D laser scanner was spliced, denoised, and registered to obtain a point cloud digital model with a point spacing of 2 mm. The pre-rainfall terrain raster data was then subtracted from the rainfall data using a raster calculation machine to obtain the spatial distribution and variation data of soil erosion and deposition in the small watershed. Analyze the hydrodynamic and erosion dynamic characteristics of mountain torrents at various sections of small watersheds; f. Repair and desilt the small watershed model according to the original model drawings, then change the number and location of the check dams. Repeat the above steps and conduct the experiment again to obtain the spatial distribution and variation data of soil erosion and deposition in the small watershed under different check dam layouts, and analyze the hydrodynamic and erosion dynamic characteristics of mountain torrents at each section.

2. The physical simulation method for the impact of silt dam layout on rainstorm and flash flood processes in small watersheds according to claim 1 is characterized in that: Also includes: In step a, a high-speed camera is installed above the silt dam model; Overflow weirs are set up in each channel of the small watershed and flow monitoring sensors are installed; an automatic runoff and sediment monitoring system is installed at the connection between the model outlet and the open channel.

3. The physical simulation method for the impact of silt dam layout on rainstorm and flash flood processes in small watersheds according to claim 2 is characterized in that: During rainfall, high-speed cameras are used to capture the distribution of mountain torrent flow fields near the silt dam; flow monitoring sensors are used to measure the mountain torrent runoff and sediment content in each channel in real time; and an automatic runoff and sediment monitoring system is used to monitor the changes in the total runoff and sediment content of mountain torrents at the outlet of the small watershed in real time.

4. The physical simulation method for the impact of silt dam layout on rainstorm and flash flood processes in small watersheds according to claim 1 is characterized in that: In step a, the silt dam model is set up according to the actual structure of a large silt dam. The silt dam model consists of four parts: a dam body, a spillway, a vertical shaft, and a stilling pool. The dam body is made of the same soil as the small watershed model, compacted layer by layer, and the dam slope is cut after reaching the design elevation; a spillway is excavated on the side of the dam body with better terrain, the joint is filled with soil, and the spillway is constructed with concrete; the vertical shaft is spliced ​​with PVC pipes, and a group of four drainage holes are set every 2.5 cm in the vertical direction of the well wall. The drainage holes have a diameter of 4 cm and are relatively staggered.

5. The physical simulation method for the impact of silt dam layout on rainstorm and flash flood processes in small watersheds according to claim 1 is characterized in that: The size of the water reservoir in step a is designed according to the amount of rainfall to be received, and its volume is 1.2 to 1.5 times the maximum amount of rainfall it can receive.

6. The physical simulation method for the impact of silt dam layout on rainstorm and flash flood processes in small watersheds according to claim 1 is characterized in that: The artificial simulated rainfall system described in step a consists of a pressure pipe and a downward-spraying simulated rainmaker. Each set of rainmakers is equipped with five sets of nozzles with different apertures, which can simulate rainfall intensities ranging from 30 to 240 mm / h and a rainfall uniformity of >85%.

7. The method for simulating the impact of silt dam layout on rainstorm and flash flood processes in small watersheds according to claim 1, characterized in that: The sections described in step a are set at the outlet of a single channel, the midstream position after the channels are aggregated, and the model outlet position.

8. A physical simulation method for the impact of silt dam layout on rainstorm and flash flood processes in small watersheds according to claim 1 or 2, characterized in that: The rainfall at the top of the slope and the ditch of the small watershed was measured 30 minutes after the rainfall to calibrate the rainfall intensity and uniformity.

9. The physical simulation method for the impact of silt dam layout on rainstorm and flash flood processes in small watersheds according to claim 1 is characterized in that: The point cloud data is collected using a target-based data acquisition method using a three-dimensional laser scanner. Each scan requires the deployment of a measuring station and a positioning ball. The scanning resolution is 1 / 4, the scanning quality is 4×, and the number of point clouds obtained is 100 million.

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