Methods for controlling local riverbed and riverbed incision

Abstract

This invention relates to a method for controlling local riverbed erosion and riverbed downcutting. The method involves excavating the entire cross-section of a river section undergoing downcutting control, and then backfilling with material whose particle size exceeds the erosion resistance particle size at the maximum flow velocity at the downcutting control section, until the backfill reaches the same elevation as the original riverbed at the downcutting control section. By excavating the riverbed downcutting control section and backfilling with material larger than its erosion resistance particle size, the riverbed is protected, and riverbed resistance is increased, making this section a "barrier section" against riverbed erosion and downcutting, effectively controlling or mitigating downcutting.

Description

Technical Field

[0001] This invention relates to the technical field of riverbed infiltration control structures and methods in riverbed maintenance, and particularly to local riverbed infiltration control methods. Background Technology

[0002] Riverbed erosion refers to the continuous erosion and decline of a riverbed's elevation. Significant riverbed erosion can lead to instability in the foundations of river-related projects such as levees, bridges, and wharves, and expose structures crossing the river, including oil pipelines, water supply lines, and subways, severely impacting the safety of these projects. Significant riverbed erosion also causes a drop in river levels, and in tidal rivers, it can lead to tidal intrusion and saltwater intrusion, affecting urban water supply security.

[0003] Currently, the main methods to suppress riverbed erosion and downcutting are engineering measures such as constructing submerged dams, locking dams, revetment belts, and bottom roughening. For details, please refer to the Chinese invention patent with publication number CN103590363A entitled "Method for Positioning and Protecting Control Nodes for Water Level Drop in Downcutting River Sections", which discloses a downcutting control method that involves arranging submerged locking dams and revetment belts on tributaries or shoals at lateral erosion nodes, and arranging bottom protection belts or submerged locking dams in the main channel at deep erosion nodes.

[0004] For example, Chinese invention patent application CN112144488A, entitled "Multi-curved arch permeable stepped energy dissipation secondary dam for preventing riverbed downcutting damage," discloses a downcutting control method that involves setting up a multi-curved arch permeable stepped energy dissipation secondary dam at an appropriate location in the river channel. Alternatively, Chinese invention patent application CN108532537A, entitled "Method for arranging boulders and terraces to control riverbed downcutting in scour sections of mountain rivers," discloses a control method that involves constructing artificial terraced deep pools in scour sections of mountain rivers undergoing downcutting control to increase river resistance, sacrifice local resources, and suppress downcutting. These downcutting control structures and methods, such as submerged dams and locking dams, generally have high dam heights, easily leading to concentrated backwater situations and creating significant local gradients and high flow velocities near engineering structures, which are detrimental to navigation and flood control.

[0005] For example, the bottom protection structure disclosed in the Chinese utility model patent with authorization announcement number CN206570755U and title "Ecological Anti-erosion and Water-blocking Bottom Protection Structure", or the Chinese invention patent with publication number CN115467290A and title "Ecological Bed Stabilizing Components, Test Device and Test Method Thereof", which involves laying a flexible protective net on the riverbed bottom wall, can stabilize the erosion base surface of the protected river section and has good adaptability to riverbed deformation. The aforementioned bottom protection belts, bottom roughening and other bottom protection structures and methods often suffer from damage such as collapse, suspension, levitation and bulging, which weakens the beach protection effect and requires subsequent maintenance projects. Summary of the Invention

[0006] To address the aforementioned problems, the present invention aims to provide a method for controlling local riverbed incision and riverbed downcutting.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] This invention provides a method for controlling local riverbed incision in a river. In the scour section of a river to be treated for riverbed incision, the entire cross-section is excavated, and then backfilled with a material with a particle size larger than the scour-resistant particle size at which the maximum flow velocity occurs at the incision control section, until the backfilling reaches the same elevation as the original riverbed at the riverbed incision control section.

[0009] As one specific implementation method, the method for calculating the erosion-resistant particle size d at the maximum flow velocity at the riverbed incision control section is as follows.

[0010]

[0011] Where: d——converted particle size (m), calculated based on spherical shape;

[0012] V—Water flow velocity (m / s);

[0013] C – Stability coefficient of the stone's movement, taken as 1.2;

[0014] g — acceleration due to gravity (m / s²) 2 );

[0015] γ s —Bulk density of riverbed sediments or erosion-resistant materials (kN / m³) 3 );

[0016] γ — Specific density of water (kN / m³) 3 ).

[0017] As one specific implementation method, based on the geological composition of the downcut control section, the scour-resistant particle size is compared with the particle size of the riverbed sediment. When the particle size of the riverbed sediment is larger than the scour-resistant particle size, the burial depth of the riverbed sediment is the excavation section depth.

[0018] As one specific implementation method, the width of the excavation section is not less than 100m, and the length of the excavation section is the width of the river channel.

[0019] As one specific implementation method, during excavation, the excavation section is connected to both banks of the river and the upstream and downstream riverbeds by slopes.

[0020] The present invention also provides a method for controlling riverbed downcutting, comprising the following steps:

[0021] Determine the basic conditions of the river channel and riverbed;

[0022] Conduct riverbed evolution analysis to identify areas with severe riverbed incision;

[0023] After avoiding the safety protection zone of water-related projects, determine the cross-sectional location of the local riverbed where riverbed downcut control measures are required;

[0024] The steps and methods for implementing the above-mentioned method for controlling local riverbed incision.

[0025] As one specific implementation method, the basic conditions of the riverbed are determined through basic data on the river's hydrology, sediment, topography, geology, and river-related engineering projects.

[0026] As one specific implementation method, the evolution of the river channel and riverbed is analyzed by examining the characteristics of the river channel cross section, the longitudinal profile of the thalweg, and the changes in riverbed scouring and deposition. Based on the comparison of underwater topographic data of the river channel over the years, the riverbed erosion process is understood, and areas with more severe riverbed erosion are identified.

[0027] As one specific implementation method, the backfill material can be a single material or a combination of multiple materials, such as boulders, pebbles, or construction waste.

[0028] As one specific implementation method, when long-distance riverbed erosion needs to be controlled, multiple riverbed erosion control sections are set up to control the entire eroded river section. The width of the excavation section at the straight part of the river is greater than the width of the excavation section at the bend of the river.

[0029] The present invention has the following beneficial effects:

[0030] ① Excavating and backfilling the riverbed incision control section with materials larger than its scour resistance size, such as stones, pebbles, and construction waste (concrete blocks, cement blocks, crushed stone, etc., with no or low pollution), protects the riverbed and increases its resistance, making this section a "barrier section" against riverbed scour and incision, effectively controlling or mitigating riverbed incision; ② The elevation of the backfilled riverbed incision control section is consistent with the original riverbed elevation, ensuring a smooth connection with the upstream and downstream riverbeds, avoiding local hydraulic concentration, and minimizing the impact on navigation and flood control; ③ The excavated usable riverbed sand and gravel resources can be used for engineering construction, achieving a coordinated approach between the development and utilization of river sand and gravel resources and river safety; ④ If construction waste (concrete blocks, cement blocks, crushed stone, etc., with no or low pollution) is used for backfilling, the recycling of construction waste can be achieved. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the downstream channel of a certain river.

[0032] Figure 2 This is a graph showing the changes in scour and sedimentation at section 33 from 2013 to 2021.

[0033] Figure 3 This is a graph showing the changes in scour and sedimentation at section 57 from 2013 to 2021.

[0034] Figure 4 This is a graph showing the changes in scour and sedimentation at section 71 from 2013 to 2021.

[0035] Figure 5 This is a graph showing the changes in scour and sedimentation at section 101 from 2013 to 2021.

[0036] Figure 6 This is a longitudinal profile of the elevation changes of the deep channel in the lower reaches of a certain river from 2013 to 2021.

[0037] Figure 7 A schematic diagram showing the changes in scouring and sedimentation in the lower reaches of a certain river from 2013 to 2021;

[0038] Figure 8 This is the engineering geological profile of section I;

[0039] Figure 9 This is the engineering geological profile of section II;

[0040] Figure 10 This is the engineering geological profile of section III;

[0041] Figure 11 This is the engineering geological profile of section IV;

[0042] Figure 12 This is the engineering geological profile of section B1;

[0043] Figure 13 This is the excavation plan of section B1;

[0044] Figure 14 This is a cross-sectional view of the B1 section excavation.

[0045] Figure 15 This is the engineering geological profile of section B6;

[0046] Figure 16 This is the excavation plan of section B6;

[0047] Figure 17 This is a cross-sectional view of the B6 section excavation.

[0048] Figure 18 Plan view of backfilling section B1;

[0049] Figure 19 This is a cross-sectional view of the backfill in section B1.

[0050] Figure 20 Plan view of backfilling section B6;

[0051] Figure 21This is a cross-sectional view of the backfill in section B6. Detailed Implementation

[0052] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments:

[0053] The method for controlling riverbed erosion in the lower reaches of a certain river includes the following steps:

[0054] (1) Determination of basic river conditions

[0055] Collect basic data on the river channel, including hydrology, sediment, topography, geology, and river-related engineering projects. Hydrological data mainly includes river flood control standards, design floods at different frequencies, design tide levels, and water level-discharge relationships; sediment data mainly includes river channel sediment content and riverbed sediment gradation; topographic data mainly includes the river channel's underwater topography over the years; geological data mainly includes river channel geological profiles; and river-related engineering data mainly includes bridges, wharves, water intakes, and pipelines crossing the river.

[0056] See Figure 1 The lower reaches of a certain river begin at Dam A1 in location A, flow through locations A, B, C, and D, and empty into the sea at location E, with a total length of approximately 117 km. The main stream, from Dam A1 in location A to C1 in location C, is approximately 60 km long and consists of six consecutive bends: Bend A2 in location A, Bend A3 in location A, Bend B1 in location B, Bend B2 in location B, Bend B3 in location B, and Bend B4 in location B. The section from Dam A1 in location A to B5 in location B is approximately 46 km long, where the terrain transitions from low mountains to hilly areas. The upper section from Dam A1 in location A to A4 in location A is approximately 15 km long, with a deeply incised, narrow valley-like channel. The riverbed consists of bedrock and pebbles interspersed with sand, with much of the bedrock exposed on both banks; the lithology is volcanic rock. The lower section of the river, from point A4 to point B5, is approximately 31 km long. The valley is relatively wide, and the riverbed consists of pebbles, coarse sand, and medium sand. Bedrock, composed of volcanic rock, is sporadically exposed on both banks. The section from point B5 to point C1, approximately 14 km long, features alternating hills and plains on both banks. The riverbed consists of medium to coarse sand, with bedrock only sporadically exposed in localized areas with steeper bank slopes. The main river-crossing structures in the lower reaches of the river include the A1 Bridge, A3 Bridge, B5 Bridge, the ring road bridge at point C, the railway bridge across the river, the water intake of the water treatment plant at point A, and the water intake of the water treatment plant at point B.

[0057] (2) Analysis of River Channel Evolution

[0058] Conduct riverbed evolution analysis, including river cross-sectional characteristics, thallopath longitudinal profile, and changes in riverbed scouring and deposition. Based on the comparison of underwater topographic data of the river over the years, understand the riverbed erosion process and identify areas with more severe erosion.

[0059] ① Cross-sectional variation analysis

[0060] The cross-sectional morphology of the main stream of a certain river in its lower reaches is mainly V or U-shaped. Several typical cross-sections were selected from the river channel for analysis. Table 1 illustrates the basic characteristics of some selected cross-sections (including cross-sections 33, 57, 71, and 101) at an elevation of 12m. Figures 2-5 The scouring and silting conditions of sections 33, 57, 71 and 101 over the years were plotted.

[0061] Section 33 is located in the transition section between curve A2 and curve A3 at location A. See [link / reference] Figure 2 The cross-section has a U-shaped morphology. From 2013 to 2018, the cross-section was completely incised, accompanied by the undulation of the thalweg, with an average incision of 3.54m. The thalweg oscillated from the right side of the cross-section to the left side, with an amplitude of 270m. From 2018 to 2019, the cross-section showed less variation, with alternating scouring and deposition, and an overall erosion state, with an average incision of 0.57m. From 2019 to 2021, the scouring of the shallow shoals in the middle of the cross-section was more significant, with an average incision of 1.09m. The cross-sectional characteristics at an elevation of 12m indicate that from 2013 to 2021, the width-to-depth ratio of the cross-section decreased year by year, while the cross-sectional area increased year by year, with the cross-sectional area in 2021 increasing by 91.0% compared to 2013.

[0062] Section 57 is located at the B1 bend section of location B, see [link / reference]. Figure 3 The cross-section is asymmetrically V-shaped, with the deep channel located on the left side. From 2013 to 2018, the cross-section was undercut across the entire riverbed, with an average incision of 1.57m. From 2018 to 2019, the deep channel showed significant scouring, with a maximum scouring depth of 6.84m. The side banks exhibited both scouring and deposition, with relatively small variations, and the entire cross-section was under scouring, with an average incision of 0.46m. From 2019 to 2021, the cross-section showed alternating scouring and deposition, with scouring as the overall dominant characteristic, and an average incision of 0.73m. The cross-sectional characteristics at an elevation of 12m indicate that from 2013 to 2021, the width-to-depth ratio of the cross-section decreased, while the cross-sectional area increased year by year, with a 61.2% increase in area in 2021 compared to 2013.

[0063] Section 71 is located at the B2 bend section of location B, see [link / reference]. Figure 4The cross-section exhibits an asymmetrical V-shape, with the deep channel located on the right side. From 2013 to 2018, the cross-section was generally in a state of uniform scouring of the shoal and channel, with an average riverbed incision of 2.27m and significant scouring in the deep channel, reaching a maximum depth of 8.54m. From 2018 to 2019, the cross-section morphology was relatively stable, with minimal changes in scouring and deposition, generally exhibiting a scouring state, with an average riverbed incision of 0.31m. From 2019 to 2021, the cross-section showed scouring of the shoals and deposition in the deep channel, with an overall scouring pattern, and an average riverbed incision of 1.27m. The cross-sectional characteristics at an elevation of 12m indicate that from 2013 to 2021, the width-to-depth ratio of the cross-section decreased, while the cross-sectional area increased year by year, with the area in 2021 increasing by 46.6% compared to 2013.

[0064] Section 101 is located in the straight river section near B5 at location B. See [link / reference] Figure 5 The cross-section is V-shaped. From 2013 to 2018, significant scouring occurred in the main channel of this cross-section, with an average incision of 2.82m across the entire cross-section. From 2018 to 2019, the cross-section morphology was relatively stable, with the thalweg slightly oscillating to the left, and the cross-section generally exhibiting scouring, with an average incision of 0.64m across the riverbed. From 2019 to 2021, significant siltation occurred in the main channel of this cross-section, with the overall cross-section showing siltation, and the average riverbed elevation rising by 0.75m. The cross-sectional characteristics at the 12m elevation indicate that from 2013 to 2021, the width-to-depth ratio of this cross-section decreased, while the cross-sectional area increased, with the cross-sectional area in 2021 increasing by 22.8% compared to 2013.

[0065] Table 1. Cross-sectional characteristics of sections 33, 57, 71, and 101 at an elevation of 12m.

[0066]

[0067] ② Longitudinal evolution analysis

[0068] Figure 6 The changes in the longitudinal profile elevation of the thalweg in a downstream main stream of a certain river from 2013 to 2021 are presented. From 2013 to 2018, the longitudinal profile elevation of the thalweg in this river section showed a downward trend along the entire length, with the most significant decrease occurring in the section from B6 to B5, reaching a maximum decrease of 15.44m. The average decrease in the thalweg elevation for the entire river section was 4.07m. From 2018 to 2019, the thalweg from the A1 dam to B1 and from B6 to C1 showed a silting trend, while the section from B1 to B6 showed a scouring trend. The average increase in the thalweg elevation for the entire river section was 0.35m. From 2019 to 2021, the changes in the thalweg elevation from the A1 dam to A4 were relatively small. The thalweg elevation near B1 showed a significant decrease, while the thalweg elevation near B6 and B5 showed a significant increase. The thalweg elevation for the entire river section showed a slight downward trend, with an average decrease of 0.03m.

[0069] ③ Analysis of scour and sedimentation changes

[0070] Table 2 shows the changes in scouring and deposition along the main stream of a certain downstream river from 2013 to 2021. Figure 7 As shown, to more clearly illustrate the changes in scouring and sedimentation in the lower reaches of a certain river from 2013 to 2021, Figure 7 A color diagram was used. See also Figure 7 The main channel of the lower reaches of a certain river is basically in a state of scouring along its entire length, with more significant downcutting in certain sections A5, B1, and B6 to B5. From 2013 to 2021, the area of ​​the riverbed in a state of siltation in the lower reaches of this river was 6.38 km². 2 The area with a siltation thickness of 2 meters or more is 1.38 km². 2 The area with a siltation thickness of 4 meters or more is 0.33 km². 2 The area of ​​the riverbed in a state of erosion is 43.29 km². 2 The area with a scour thickness greater than or equal to 3m is 25.11km². 2 The area with a scour thickness greater than or equal to 6 meters is 11.14 km². 2 From 2013 to 2021, the scour area of ​​the river section accounted for 87.16% of the total riverbed area. The river section was basically in a state of uniform scour along the channel and shoals, with an average riverbed elevation drop of 3.51 meters and a total scour volume of 173,208,100 cubic meters. 3 .

[0071] Table 2. Changes in scouring and sedimentation in the lower reaches of a certain river from 2013 to 2021

[0072]

[0073] (3) Analysis of river channel geological conditions

[0074] Conduct geological composition analysis of river channels and riverbeds. Based on river geological profile data, analyze the composition and distribution characteristics of riverbed sediments, such as the distribution, layer thickness, and grain size of different sediments, including riverbed silt, fine sand, medium sand, coarse sand, sand mixed with gravel, pebbles, and weathered granite.

[0075] The geological conditions of the river can be seen from the engineering geological profile of the river channel. Figures 8-11 Engineering geological profiles of selected sections (including sections I, II, III, and IV) are shown as examples.

[0076] From the engineering geological profiles of the river channel, it can be seen that in the section from A1 to A7 at location A, the upper strata consist of medium sand and pebbles; in the section from A7 to B1, the upper strata consist of medium sand, sand interbedded with gravel, and pebbles. Specifically, in the section from A1 to A6 at location A, the medium sand layer is relatively thin, ranging from 2.65m to 7.11m, while in the section from A6 to B1, the medium sand layer is slightly thicker, ranging from 5.10m to 11.73m. The pebble layer in the section from A1 to A7 at location A is 4.25m to 6.40m thick, with some sections being even thicker. The sand interbedded with gravel layer in the section from A7 to B1 is 5.27m to 6.90m thick.

[0077] Most of the riverbed from B1 to C1, including areas B1 to B8, B9 to B10, and B5 to C1, consists of medium sand and sand interbedded with gravel. The medium sand layer has a maximum thickness of 8.80m to 13.18m, with an average maximum thickness of 10.82m. Below the medium sand layer, the average maximum thickness of the sand interbedded with gravel is greater than 4.70m, with some boreholes revealing a maximum thickness greater than 8.05m. In the upstream section from B8 to B9, the upper strata consist of medium sand and pebbles. The medium sand layer has a maximum thickness of 7.02m to 13.36m, with an average maximum thickness of 10.87m. The pebble layer has an average maximum thickness greater than 4.05m, with some boreholes revealing a maximum thickness greater than 5.50m. In the middle section of this river, near point B11 in area B, the maximum thickness of the medium sand layer reaches 7.50m to 11.00m, with an average maximum thickness of 9.31m. Silt appears below the medium sand layer, and boreholes reveal a maximum layer thickness greater than 6.80m.

[0078] (4) Determination of the control section for riverbed incision

[0079] Based on the analysis of riverbed evolution, areas with severe riverbed incision were identified. Taking into account the safety protection range of water-related projects such as bridges, wharves, water intakes, and pipelines crossing the river, and avoiding the safety protection range of water-related projects, the cross-section locations for riverbed incision control measures were determined.

[0080] Based on the riverbed evolution, and considering typical cross-sections, longitudinal profiles of the deep channel, and changes in riverbed scouring and deposition, the following river sections show significant downcutting: section A5 in area A, section B1 in area B, and section B6 to B5 in area B. Section A5 in area A contains the A3 Bridge in area A and a water intake point for a certain river in area A. The section B6 to B5 in area B, near the B5 cross-section, contains the B5 Bridge in area B, the B5 hydrological station in area B, and the B5 water intake point in area B, all of which have their legally protected areas. Therefore, the selection of control sections should avoid impacting these facilities. Sections B1 and B6 in area B show significant downcutting, and since these two sections are far from the protected areas of the bridges and water intake points, they are designated as the control sections for the downcutting of the riverbed.

[0081] (5) Excavate the entire section of the determined riverbed incision control section.

[0082] The entire cross-section of the riverbed incision control section is excavated. The width of the excavation section (longitudinal length along the river channel) is not less than 100m, and can be determined based on the actual conditions of the river channel, such as the control effect of the excavation section on the river morphology upstream and downstream, or the scouring and deposition conditions of the upstream and downstream riverbeds, or in conjunction with mathematical or physical model experiments of the river channel. The length of the excavation section (lateral width along the river channel) is the width of the river channel. The depth of the excavation section (depth from the riverbed surface downwards) is determined according to the distribution of riverbed sediments. Specifically, the scour-resistant particle size is calculated when the maximum flow velocity occurs at the riverbed incision control section (the flow velocity under the design flood condition corresponding to the flood control standard). The scour-resistant particle size is compared with the particle size of the riverbed sediments. When the particle size of the riverbed sediments is greater than the scour-resistant particle size, the burial depth of the riverbed sediments at this time (based on the riverbed surface) is the depth of the excavation section. The excavation section is connected to both banks of the river and the upstream and downstream riverbeds with stable slopes to avoid causing the collapse of the riverbanks and riverbeds.

[0083] ① Excavate section B1.

[0084] Excavation was carried out at section B1, which is a bend in the river channel and has a significant effect on controlling the river's morphology upstream and downstream. Referring to existing data on riverbank protection zones (with a width exceeding 100m), the excavation section width (longitudinal length along the river channel) was set at 100m, and the excavation section length L (transverse width along the river channel) was equal to the river channel width of 580m. Under a 50-year flood standard, the maximum flow velocity at this section was 3.03m / s. The erosion resistance particle size d was calculated using the following formula:

[0085]

[0086] Where: d——converted particle size (m), calculated based on spherical shape;

[0087] V—Water flow velocity (m / s);

[0088] C – Stability coefficient of the stone's movement, taken as 1.2;

[0089] g — acceleration due to gravity (m / s²) 2 );

[0090] γ s —Bulk density of riverbed sediments or erosion-resistant materials (kN / m³) 3 );

[0091] γ — Specific density of water (kN / m³) 3 ).

[0092] Specifically, based on the above formula, the erosion-resistant particle size is obtained through the following two methods:

[0093] Firstly, based on the particle size (the type of material in the cross-section geological composition is known, and thus the material's bulk density and other parameters are known), its scour velocity can be estimated. This allows us to obtain the scour velocities for different particle sizes (fine sand, medium sand, coarse sand, pebbles, etc.). The particle size (or a certain type of sand) that is equal to or greater than the maximum velocity after the scour velocity is calculated is the scour particle size.

[0094] Secondly, assuming the material is a specific type, such as pebbles, then the density and other parameters of the pebbles are known. The corresponding particle size is estimated using the maximum flow rate. If the calculated particle size falls within the range of pebble particle size, it is the erosion-resistant particle size. If the calculated particle size is smaller than that of pebble, it means that the density is not suitable and the assumed particle size is too large. It is necessary to continue to assume a smaller density (such as coarse sand), and then continue to use the maximum flow rate to estimate the particle size. If the calculated particle size falls within the range of coarse sand particle size, it is the erosion-resistant particle size.

[0095] Therefore, the calculated erosion-resistant particle size is 0.20m. This is combined with the geological composition of section B1, which can be found in [reference needed]. Figure 12 The engineering geological profile of section B1 shows that the strata with a particle size greater than the required erosion resistance are buried at a depth of 7.5m. Therefore, the excavation depth (from the riverbed surface downwards) is 7.5m. During excavation, the excavation section will connect with both banks of the river and the upstream and downstream riverbeds at a 1:3 slope to avoid causing riverbank and riverbed collapse. The excavation plan of section B1 is shown below. Figure 13 Cross-sectional view as follows Figure 14 As shown.

[0096] ② Excavate section B6.

[0097] Excavation was carried out at section B6. The B6 section and its downstream section show significant downcutting, and the downstream section is relatively straight, meaning its control over the river course is limited. Therefore, the width of the excavation section (longitudinal length along the river channel) should be wider. Thus, the excavation section width was set at 150m, and the excavation section length L (transverse width along the river channel) is equal to the river channel width of 647m. Under a 50-year flood standard, the maximum flow velocity at this section is 3.31m / s. The erosion resistance particle size d was calculated using the following formula:

[0098]

[0099] Where: d——converted particle size (m), calculated based on spherical shape;

[0100] V—Water flow velocity (m / s);

[0101] C – Stability coefficient of the stone's movement, taken as 1.2;

[0102] g — acceleration due to gravity (m / s²);

[0103] γs —Bulk density of riverbed sediments or erosion-resistant materials (kN / m³) 3 );

[0104] γ — Specific density of water (kN / m³) 3 );

[0105] The specific method is the same as above and will not be repeated. The calculated erosion-resistant particle size is 0.24m. Combined with the geological composition of section B6, please refer to [reference needed]. Figure 15 The engineering geological profile of section B6 shows that the strata with a particle size greater than the required erosion resistance are buried at a depth of 10m. Therefore, the excavation depth (from the riverbed surface downwards) is 10m. During excavation, the excavation section will connect with both banks of the river and the upstream and downstream riverbeds at a 1:3 slope to avoid causing riverbank and riverbed collapse. The excavation plan of section B6 is shown below. Figure 16 Cross-sectional view as follows Figure 17 As shown.

[0106] (6) Backfilling of riverbed incision control sections

[0107] Backfilling shall be carried out on the excavated riverbed incision control section. The backfill material can be boulders, pebbles, construction waste (concrete blocks, cement blocks, crushed stone, etc., with no or low pollution), etc., and can be in the form of a single material or a combination of multiple materials. The particle size of the backfill material should be greater than the scour-resistant particle size when the maximum flow velocity occurs at the riverbed incision control section (the flow velocity under the design flood condition corresponding to the flood control standard). The backfill elevation should be consistent with the original riverbed elevation of the riverbed incision control section to ensure a smooth connection with the riverbed elevation of its upstream and downstream sections.

[0108] ① Backfill the excavated section B1.

[0109] Backfilling was carried out on the excavated section B1. Based on calculations showing an erosion resistance particle size of 0.20 μm, the backfill material was determined to be a combination of boulders and pebbles with a particle size greater than 0.20 μm. Boulders were used at the bottom of the section, and pebbles at the top. The particle size of all backfill materials was greater than the erosion resistance particle size. The upstream riverbed elevation of this section is -1.0 m, and the downstream riverbed elevation is -1.1 m. The backfill section elevation smoothly connects with its upstream and downstream elevations, connecting to the upstream elevation of -1.0 m and the downstream elevation of -1.1 m. The backfill plane of section B1 is shown below. Figure 18 Cross-sectional view as follows Figure 19 As shown.

[0110] ② Backfill the excavated section B6.

[0111] Backfilling was carried out on the excavated section B6. Based on calculations, the erosion-resistant particle size was determined to be 0.24m, and the backfill material was selected to be pebbles with a particle size greater than 0.24m. The particle size of the backfill material is larger than the erosion-resistant particle size. The upstream riverbed elevation of this section is -4.0m, and the downstream riverbed elevation is -4.15m. The elevation of the backfill section is smoothly connected to its upstream and downstream elevations, connecting to the upstream elevation of -4.0m and the downstream elevation of -4.15m. The backfill plane of section B6 is shown below. Figure 20 Cross-sectional view as follows Figure 21 As shown.

[0112] The above description is merely a specific embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made based on the content of the present invention specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for controlling local riverbed incision, characterized by: In the river section undergoing riverbed erosion control, the erosion-resistant particle size at the maximum flow velocity at the erosion control section is calculated. Based on the geological composition of the erosion control section, the erosion-resistant particle size is compared with the particle size of the riverbed sediment. When the riverbed sediment particle size is larger than the erosion-resistant particle size, the burial depth of the riverbed sediment is the excavation section depth, and full-section excavation is carried out. Then, material with a particle size larger than the erosion-resistant particle size at the maximum flow velocity at the erosion control section is backfilled until the elevation is consistent with the original riverbed elevation at the riverbed erosion control section.

2. The method for controlling local riverbed incision according to claim 1, characterized in that: Calculate the erosion-resistant particle size d at the maximum flow velocity control section of the riverbed incision. In the formula: d—converted particle size (m), calculated based on spherical shape; V—Water flow velocity (m / s); C – Stability coefficient of the stone's movement, taken as 1.2; g — acceleration due to gravity (m / s²) 2 ); γs — the bulk density of riverbed sediments or erosion-resistant materials (kN / m³); γ — Specific density of water (kN / m³); Using the above formula for calculating the erosion-resistant particle size d, the erosion-resistant flow velocity can be estimated based on the erosion-resistant particle size d. The particle size with an erosion-resistant flow velocity equal to or greater than the maximum flow velocity is determined as the erosion-resistant particle size. Alternatively, based on the material, the corresponding particle size can be estimated using the maximum flow velocity. If the calculated particle size falls within the particle size range of the specific material, it is determined as the erosion-resistant particle size.

3. The method for controlling local riverbed incision according to claim 1, characterized in that: The width of the excavation section shall not be less than 100m, and the length of the excavation section shall be equal to the width of the river channel.

4. The method for controlling local riverbed incision according to claim 1, characterized in that: During excavation, the excavation section is connected to both banks of the river and the upstream and downstream riverbeds by slope.

5. A method for controlling riverbed incision, characterized in that, Includes the following steps: Determine the basic conditions of the river channel and riverbed; Conduct riverbed evolution analysis to identify areas with severe riverbed incision; After avoiding the safety protection zone of water-related projects, determine the cross-sectional location of the local riverbed where riverbed downcut control measures are required; The scour-resistant particle size at the maximum flow velocity of the downcut control section is calculated, and the scour-resistant particle size is compared with the particle size of the riverbed sediments based on the geological composition of the downcut control section. When the particle size of the riverbed sediments is greater than the scour-resistant particle size, the burial depth of the riverbed sediments at this time is the excavation section depth, and full-section excavation is carried out. During excavation, the excavation section is connected to both banks of the river and the upstream and downstream riverbeds with slopes respectively. Then backfill with material whose particle size is larger than the scour-resistant particle size when the maximum flow velocity occurs at the incision control section, and backfill to the same level as the original riverbed elevation of the riverbed incision control section. When long-distance riverbed erosion occurs and control is required, multiple riverbed erosion control sections are set up to control the entire eroded section. The excavation section width at the straight section of the river is greater than the excavation section width at the bend of the river.

6. The method for controlling riverbed erosion according to claim 5, characterized in that: The basic conditions of the riverbed are determined by the hydrological, sediment, topographic, geological, and basic data of river-related projects.

7. The method for controlling riverbed erosion according to claim 5, characterized in that: The riverbed evolution is analyzed by examining the characteristics of the river cross section, the longitudinal profile of the thalweg, and the changes in riverbed scouring and deposition. Based on the comparison of underwater topographic data of the river over the years, the riverbed incision process is understood, and areas with severe riverbed incision are identified.

8. The method for controlling riverbed erosion according to claim 5, characterized in that: Calculate the erosion-resistant particle size d at the maximum flow velocity control section of the riverbed incision. In the formula: d—converted particle size (m), calculated based on spherical shape; V—Water flow velocity (m / s); C – Stability coefficient of the stone's movement, taken as 1.2; g — acceleration due to gravity (m / s²) 2 ); γs — the bulk density of riverbed sediments or erosion-resistant materials (kN / m³); γ — Specific density of water (kN / m³); Using the above formula for calculating the erosion-resistant particle size d, the erosion-resistant flow velocity can be estimated based on the erosion-resistant particle size d. The particle size with an erosion-resistant flow velocity equal to or greater than the maximum flow velocity is determined as the erosion-resistant particle size. Alternatively, based on the material, the corresponding particle size can be estimated using the maximum flow velocity. If the calculated particle size falls within the particle size range of the specific material, it is determined as the erosion-resistant particle size.

9. The method for controlling riverbed erosion according to claim 5, characterized in that: The width of the excavation section shall not be less than 100m, and the length of the excavation section shall be equal to the width of the river channel.

10. The method for controlling riverbed erosion according to claim 5, characterized in that: The backfill material can be a single material or a combination of multiple materials, such as boulders, pebbles, or construction waste.

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