Restoration method of fish habitat in mountainous rivers based on numerical simulation optimization

Abstract

The present invention relates to the technical field of habitat restoration for fish habitats in mountainous rivers, specifically to a method for restoring fish habitats in mountainous rivers based on numerical simulation optimization. The method comprises the following steps: obtaining habitat data for fish habitats in mountainous rivers and implementing preliminary ecological restoration measures on the habitats; constructing a numerical simulation model to predict the evolution of scouring and silting in the fish habitats in mountainous rivers after the preliminary ecological restoration within a set period, and identifying areas where the degree of scouring and silting evolution within the set period meets a preset threshold; modifying the riverbed subsurface in the identified areas based on target fish species, evaluating the habitat improvement effect of the preliminary ecological restoration measures and riverbed subsurface modification using a habitat suitability model, and completing the restoration of fish habitats in mountainous rivers based on the evaluation results. The present invention improves the effectiveness, sustainability, and scientific nature of fish habitat restoration in mountainous rivers by combining dredging, spur dikes, and subsurface modification with numerical simulation optimization.

Description

Technical Field

[0001] The present invention relates to the technical field of restoration of fish habitats in mountainous rivers, and in particular to a method for restoration of fish habitats in mountainous rivers based on numerical simulation optimization. Background Art

[0002] Mountain rivers, due to their unique topography and landforms, such as high elevations and complex terrain, have developed channels characterized by steep gradients and high sinuosity. Their riverbeds are often composed primarily of primary bedrock, pebbles, and coarse sand. Hydrologically, these rivers exhibit significant seasonal variations in flow and rapid flooding. This unique natural environment fosters diverse habitat types, including rapids, shallows, deep pools, and rich coastal vegetation. These habitats provide valuable habitats for numerous fish, particularly rare species, and serve as crucial ecological corridors for maintaining regional biodiversity. However, with the intensification of human activities such as water conservancy projects, in-channel sand mining, and other forms of river channel modification, fish habitats in mountain rivers are facing significant encroachment and damage, significantly impacting the reproduction and survival of river fish populations. Current fish habitat restoration efforts, such as dismantling partial dams, modifying local river morphology, or implementing bioremediation, often lack a systematic consideration of the specific hydrological, geomorphological, and ecological characteristics of mountain rivers, resulting in limited universality and specificity. On the other hand, the large gradient and high meandering characteristic of mountain rivers make their water and sediment transport patterns and riverbed evolution processes extremely complex. The current planning and design of habitat restoration measures and the selection of implementation areas rely more on empirical judgment and fail to fully integrate the dynamic processes of river water and sediment movement for scientific demonstration. This not only makes it difficult to ensure the long-term sustainability of restoration results, but also easily leads to poor restoration results or even negative impacts due to insufficient predictions of complex riverbed evolution. Summary of the Invention

[0003] The purpose of the present invention is to provide a method for restoring fish habitats in mountain rivers based on numerical simulation optimization. By combining dredging, spur dikes and bottom modification, and combining numerical simulation optimization, the method systematically improves the effectiveness, sustainability and scientific nature of fish habitat restoration in mountain rivers, providing a new solution for the protection of rare fish.

[0004] The present invention is achieved through the following technical solutions:

[0005] A method for restoring fish habitats in mountainous rivers based on numerical simulation optimization includes the following steps:

[0006] Obtain habitat data for fish habitats in mountain rivers and implement preliminary ecological restoration measures such as dredging rivers and constructing diversion spur dikes in mountain river fish habitats;

[0007] Construct a numerical simulation model to predict the evolution of scouring and silting of restored mountain river fish habitats over a set period, and based on the scouring and silting evolution results, identify areas where the degree of scouring and silting evolution within the set period meets a preset threshold;

[0008] Based on the habitat requirements of target fish, the riverbed substrate of the identified areas is modified. Through the habitat suitability model, the improvement effect of the fish habitat in mountain rivers under the combined effects of preliminary ecological restoration measures and riverbed substrate modification is evaluated. Based on the evaluation results, the restoration of the fish habitat in mountain rivers is completed.

[0009] Optionally, the preliminary ecological restoration measures include excavating and dredging the sediment accumulation area and constructing a diversion spur dike;

[0010] The excavation and dredging of the sediment accumulation area is specifically as follows:

[0011] Excavation is carried out in areas where the hydrodynamic conditions of mountain river fish habitats do not meet the fish habitat requirements, so that the hydrodynamic conditions of mountain river fish habitats are improved after excavation. The hydrodynamic conditions include: water depth of mountain river fish habitats and flow velocity of mountain river fish habitats. The fish habitat requirements vary depending on the fish species, and the range of hydrodynamic conditions varies.

[0012] Optionally, the construction of the diversion spur dike is specifically as follows:

[0013] One or more spur dikes are constructed at the desired water flow adjustment locations in the fish habitats of mountain rivers, and the length, spacing, height and construction materials of the spur dikes are determined.

[0014] Optionally, the constructing of a numerical simulation model specifically includes:

[0015] Based on numerical simulation, the following models were constructed: hydrodynamic model, sediment transport model and terrain evolution model;

[0016] The hydrodynamic model, the sediment transport model and the terrain evolution model are coupled to form the numerical simulation model.

[0017] Optionally, the specific calculation formula of the hydrodynamic model is:

[0018]

[0019]

[0020]

[0021]

[0022]

[0023]

[0024] in, is the body-fitting coordinate, is the height of the free surface above the reference plane, is the depth from the reference plane to the river bottom, Represents the total water depth, For time, for The depth-averaged velocity in the direction, for The depth-averaged velocity in the direction, for Coordinate conversion coefficient of direction, for Coordinate conversion coefficient of direction, is the flow change value caused by water inflow and outflow in the calculation unit, and are the source and sink terms of water flow within the calculation unit, is the water density, for The pressure gradient in the direction of for The pressure gradient in the direction of for The turbulent momentum flux in the direction of for η The turbulent momentum flux in the direction of for The momentum source and sink terms in the direction, for The momentum source and sink terms in the direction, is the acceleration due to gravity, is the Xie Cai coefficient of the two-dimensional shallow water equation, for direction of the momentum flux caused by the secondary flow, for Direction of the momentum flux caused by the secondary flow.

[0025] Optionally, the specific calculation formula of the sediment transport model is:

[0026]

[0027]

[0028]

[0029]

[0030] in, is the sediment transport rate, is the sediment density, is the relative density of sediment, is the critical dimensionless shear stress for sediment initiation, is the median particle size of sediment, In order to consider the hidden exposure coefficient between sediment components, is the dimensionless shear stress of the riverbed, is the water flow velocity, is Xie Cai coefficient, is the efficiency coefficient, is the particle size-related coefficient, The characteristic particle size is that 90% of the sediment is smaller than this particle size.

[0031] Optionally, the terrain evolution model has a specific calculation formula as follows:

[0032]

[0033] in, is the sediment porosity, is the change in riverbed elevation, is the geomorphic acceleration factor, 、 are the sediment transport amounts per unit width along the x and y directions, respectively.

[0034] Optionally, the numerical simulation model is constructed to predict the evolution of scouring and silting of the restored mountain river fish habitat within a set period, specifically:

[0035] The river topography and hydrological conditions after the implementation of preliminary ecological restoration measures are used as input, and simulation calculations are performed through a coupled numerical simulation model. The scouring and deposition thickness or elevation changes at each point on the riverbed at the end of the set period are output to characterize the scouring and deposition evolution results.

[0036] Optionally, the specific calculation formula of the habitat suitability model is:

[0037]

[0038]

[0039] in, 、 and are the habitat suitability indices of water depth, flow velocity and riverbed sediment in the ith grid in the simulation area; is the comprehensive habitat fitness index of the i-th grid, is the area of ​​the i-th grid, is the weighted effective habitat area, and n is the total number of grids in the simulation area.

[0040] Optionally, the habitat suitability model is used to evaluate the improvement effect of fish habitat in mountain rivers under the combined effects of preliminary ecological restoration measures and riverbed modification, specifically:

[0041] Obtain data on water depth, flow velocity distribution, and riverbed type in mountain river fish habitats after preliminary ecological restoration measures and riverbed modification;

[0042] Based on the habitat suitability curve of target fish for water depth, flow velocity and riverbed type data, the habitat suitability index of each evaluation unit is calculated;

[0043] The comprehensive habitat suitability index of each evaluation unit was calculated by multi-factor combination method;

[0044] Calculate the weighted effective habitat area of ​​the entire restoration area;

[0045] The HSI and WUA calculated after the repair are compared with the corresponding values ​​before the repair to obtain the evaluation results.

[0046] The technical solution of the present invention has at least the following advantages and beneficial effects:

[0047] The present invention fully considers the geomorphological and hydrological characteristics of mountain rivers, such as high slope and strong disturbance, and systematically proposes a set of combined fish habitat restoration measures and scientific implementation sequence of "dredging river channels - building diversion dikes - optimizing and laying suitable bottom sediments". It can not only effectively improve the adverse water flow conditions caused by silt deposition, but also regulate water and sediment through dikes, maintain the dredging effect and create a hydrodynamic environment preferred by fish. Combined with bottom sediment transformation, it can comprehensively improve the habitat quality. Its restoration effect is more significant and lasting than that of a single measure, providing an innovative and efficient solution for the effective protection and population restoration of rare fish resources in mountain rivers. In addition, the present invention innovatively incorporates numerical simulation technology throughout the entire process of design, implementation and evaluation of the restoration plan. By constructing a mathematical model of water and sediment to accurately predict riverbed evolution, the optimal location and timing of bottom sediment transformation are selected. This not only greatly improves the pertinence and effectiveness of the restoration measures, ensures the long-term stability and sustainability of the restoration results, but also significantly reduces the trial and error cost of the restoration project, providing a scientific basis for the quantitative evaluation of the restoration effect. More importantly, the present invention is always guided by the actual habitat needs of the target fish. The proposed restoration measures and parameters can be flexibly adjusted according to the biological characteristics and habitat preferences of different protected fish. It is highly operational and widely applicable, providing important technical support for ecological restoration projects in various mountain rivers. It also provides valuable scientific solutions and engineering practice guidance on how to successfully create and maintain alternative habitats in tributaries under the current context of hydropower development. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 A schematic diagram of the process of restoring fish habitats in mountainous rivers based on numerical simulation optimization provided by the present invention;

[0049] Figure 2 A topographic map of the river section where the SM River spawning ground is located and a schematic diagram of the spawning ground are provided for the specific implementation examples provided by the present invention;

[0050] Figure 3 A schematic diagram of the suitability curve of representative fish species in a mountain river to various important habitat factors of the river provided by the present invention;

[0051] Figure 4 A schematic diagram of the fish habitat suitability status before habitat restoration in the SM River spawning ground provided by the present invention;

[0052] Figure 5 A schematic diagram comparing the river topography before and after the dredging project is implemented in the SM River spawning ground section provided by the present invention;

[0053] Figure 6 This is a schematic diagram of the layout of diversion spurs in the spawning ground section of the SM River provided by the present invention;

[0054] Figure 7 A schematic diagram comparing the topographic evolution of the river section six months after the spawning grounds of the SM River provided by the present invention are provided with or without diversion spurs;

[0055] Figure 8 Schematic diagram of the bottom modification area and modification method in the SM River spawning ground provided by the present invention;

[0056] Figure 9 This is a schematic diagram comparing the fish habitat suitability of the SM River spawning ground section provided by the present invention with or without habitat restoration measures taken. DETAILED DESCRIPTION

[0057] To make the objectives, technical solutions, and advantages of the present invention more apparent, the following will provide a clear and complete description of the technical solutions of the present invention in conjunction with the accompanying drawings. It should be understood that the description is only a portion of the present invention, not all of it. The components of the present invention generally described and illustrated in the drawings herein may be arranged and designed in a variety of different configurations.

[0058] like Figure 1 As shown, the present invention provides one embodiment: a method for restoring fish habitats in mountain rivers based on numerical simulation optimization, the method comprising the following steps:

[0059] Obtain habitat data for mountain river fish habitats and implement preliminary ecological restoration measures for mountain river fish habitats;

[0060] Construct a numerical simulation model to predict the evolution of scouring and silting of fish habitats in mountain rivers after restoration using preliminary ecological restoration measures over a set period, and based on the scouring and silting evolution results, identify areas where the degree of scouring and silting evolution meets a preset threshold within the set period;

[0061] Based on the habitat requirements of target fish, the riverbed substrate of the identified areas is modified. Through the habitat suitability model, the improvement effect of the fish habitat in mountain rivers under the combined effects of preliminary ecological restoration measures and riverbed substrate modification is evaluated. Based on the evaluation results, the restoration of the fish habitat in mountain rivers is completed.

[0062] In this embodiment, the present invention gradually improves the habitat conditions of fish in mountain rivers by excavating silted river channels, laying diversion spurs, and modifying the riverbed bottom at appropriate locations. The main steps are as follows: (1) On-site survey of the river channel topography and bottom conditions of the fish habitat, establish a mathematical model to simulate the important fish habitat indicators such as river flow velocity and water depth in the fish habitat, and evaluate the habitat status based on the fish habitat suitability model. (2) In view of the narrowing of some river channels caused by silt accumulation and the water flow conditions that are unfavorable for fish activities, the river channel is dredged by excavating the riverbed to increase the flow area of ​​the river channel and improve the water flow conditions in the habitat. (3) According to the river channel form and silt accumulation characteristics, a diversion spur is selected to adjust the water flow direction and sediment transport law, strengthen the main channel of the river and slow down the sediment accumulation, thereby shaping the river landform and hydrodynamic conditions preferred by fish. Based on existing research, the following principles guide the placement of diversion spur dikes: Spur dikes are typically placed crisscrossing the banks of a river to induce a meander in the main stream and regulate sediment transport patterns. Research indicates that in small rivers and streams, the distance from the top of a diversion spur dike to the opposite bank should be approximately 70% to 80% of the original channel width; that is, the spur dike length should not exceed 30% of the river width. Numerical simulations have investigated the effect of spur dike spacing on river ecological restoration. Results show that a spur dike spacing of four times the spur dike length maximizes suitable habitat area and achieves the best restoration results. The upstream side of a diversion spur dike is typically positioned at an angle of approximately 30° to the riverbank, directing water flow at a suitable velocity toward the central channel. The downstream side is typically positioned at an angle of approximately 60° to protect that side of the riverbank from erosion. (4) Construct a model of water and sediment transport and riverbed evolution in the habitat river section to simulate the evolution of riverbed erosion and deposition under natural flow. Select river sections with relatively mild erosion and deposition, and modify the riverbed substrate according to the living habits of fish to further create a suitable habitat for fish. (5) Use the habitat suitability model to simulate the fish habitat suitability before and after restoration of the habitat river section, and compare and evaluate the actual effects of habitat restoration measures.

[0063] In a specific implementation based on the above embodiment, the mathematical simulation model includes a hydrodynamic model, a sediment transport model, a terrain evolution model, and a habitat suitability model.

[0064] The river channel boundary of mountain rivers has complex curvature. It is difficult to fit the river channel boundary smoothly using rectangular grids, which may lead to large discrete errors in the calculation process. Therefore, in the horizontal direction, the model uses orthogonal curved grids to make the grid fit the river channel boundary as smoothly as possible. The corresponding coordinate system is the orthogonal curved coordinate system ( ξ , η ), that is, body-fitted coordinates, which are converted to rectangular coordinates (x, y) by the conversion coefficient and Finish.

[0065] The model equations are described as follows:

[0066] Continuity equation for the hydrodynamic model:

[0067]

[0068] in, is the height of the free surface above the reference plane z=0, in meters, is the depth from the reference plane to the river bottom, in meters. is the total water depth, For time, for The depth-averaged velocity in the direction, for Depth-average velocity in the direction, in m·s -1 , for Coordinate conversion coefficient of direction, for Coordinate conversion coefficient of direction, and The expression is:

[0069]

[0070]

[0071] The flow rate change value caused by water inflow and outflow in the calculation unit, unit is m 3 ·s -1 :

[0072]

[0073] in, and are the source and sink terms of water flow within the calculation unit, respectively, with a unit of 1·s -1 , the model built in this embodiment does not consider rainfall and evaporation, so Only with and Related.

[0074] Momentum equation for the hydrodynamic model:

[0075] and The depth-averaged momentum equations in the directions are:

[0076]

[0077]

[0078] in, is the water density, unit is kg·m -3 , for Pressure gradient in the direction, unit: kg·m -2 ·s -2 , for The pressure gradient in the direction of for Turbulent momentum flux in the direction, unit: m·s -2 , for η The turbulent momentum flux in the direction of for The momentum source and sink terms in the direction, for Momentum source and sink terms in the direction, unit: m·s -2 , is the acceleration due to gravity, is the Xie Cai coefficient of the two-dimensional shallow water equation, unit is m 1 / 2 ·s -1 , for direction of the momentum flux caused by the secondary flow, for Direction of momentum flux caused by secondary flow, unit: m·s -2 The hydrodynamic model includes boundary conditions for the inflow and outflow, including the flow rate at the inflow boundary and the water level at the outflow boundary. The inflow boundary flow process is the flow process of the study section in a normal year, measured by a hydrological station, while the downstream water level is derived from the flow-water level curve at the section.

[0079] Sediment transport model, during river sediment transport, the expression of sediment transport rate S is:

[0080]

[0081] in, is the sediment transport rate, is the sediment density, unit: kg·m -3 , is the relative density of sediment, is the critical dimensionless shear stress for sediment initiation, which is 0.047 here. is the median particle size of sediment, In order to consider the hidden exposure coefficient between sediment components, is the dimensionless shear stress of the riverbed, which is:

[0082]

[0083] in, is the water flow velocity, in m·s -1 , is Xie Cai coefficient, unit is m 1 / 2 ·s -1 , is the efficiency coefficient, which is:

[0084]

[0085] in, is the particle size-related coefficient, and its calculation formula is:

[0086]

[0087] in, The characteristic particle size at which 90% of the sediment is smaller than this particle size. The sediment boundary condition is the sediment concentration, and the measured data from the hydrological station in the river section during a normal water year are used.

[0088] In the terrain evolution model, the riverbed topography is dynamically updated at each calculation time step. Subsequent changes in the topography will also affect the calculation of hydrodynamic conditions. After each calculation time step, the riverbed elevation is updated using the Exner equation based on sediment mass conservation. The Exner equation is expressed as follows:

[0089]

[0090] in, is the sediment porosity, set to 0.4, is the change in riverbed elevation, in m, is the geomorphic acceleration factor, 、 are the sediment transport capacity in the x and y directions per unit width, in kg·m -1 ·s -1 .

[0091] The habitat suitability model combines simulation results from hydrodynamics, sediment transport, and topographic evolution models with fish suitability curves for habitat indicators such as hydrodynamics and bottom sediments to establish a fish habitat suitability assessment model. Fish habitat suitability curves are developed based on the physiological and behavioral responses of fish to various habitat indicators. They describe the survival and reproductive capacity of fish under different environmental conditions and are defined using a value between 0 and 1 to indicate the degree of preference of a fish for a single habitat factor, with 0 indicating no preference for a specific key habitat element and 1 indicating the highest preference for that key habitat element.

[0092] Based on the simulation results of each habitat indicator in the simulation area, the suitability index SI (Suitability Index) of each habitat indicator in each grid in the simulation area is calculated in combination with the fish suitability curve. Then, the suitability index of a single habitat indicator is converted into a comprehensive habitat suitability index HSI (Habitatsuitability Index) that can reflect the overall suitability of the river through the "product method". Combining the grid area and the habitat suitability index, the weighted effective habitat area WUA (Weighted Useable Area, m 2 ), and then evaluate the fish habitat suitability of the study river section.

[0093] This example uses water depth, flow velocity, and riverbed sediment particle size as key habitat indicators for evaluating the habitat suitability of dam-removed river sections. The fish habitat suitability curve is used to calculate the suitability index (SI) for each indicator. The formulas for calculating the habitat suitability index (HSI) and the weighted effective habitat area (WUA) are as follows:

[0094]

[0095]

[0096] in, 、 and are the habitat suitability indices of water depth, flow velocity and riverbed sediment in the ith grid in the simulation area; is the comprehensive habitat fitness index of the i-th grid, is the area of ​​the ith grid, in m 2 , is the weighted effective habitat area, and n is the total number of grids in the simulation area. The comprehensive habitat suitability index (HSI) was tested by comparing the results of the river habitat survey. The results showed that areas with an HSI ≥ 0.8 had relatively good habitats and were classified as highly suitable. When 0.8 > HSI ≥ 0.6, the suitability was suitable. When HSI < 0.2, the area had poor habitats and was classified as unsuitable.

[0097] In this embodiment, an application example is also provided: the application example is selected as a fish spawning ground on the SM River, a first-level tributary of a large river in the mountainous area of ​​southwest China. Figure 2 As shown in the figure, the representative fish species of a mountain river are selected as target fish species. Figure 3 As shown in Figure 2, the peak spawning period of this fish is September. Its habitat suitability curve for water depth, flow rate and riverbed is as follows: Figure 3 .

[0098] The specific steps of the entire application example are as follows:

[0099] like Figure 2 As shown in the figure, we measured the topography and bottom conditions of the river sections where the fish spawning grounds are located, collected multi-year hydrological data from the SM River Basin, and calculated the river conditions in normal water years. We established a hydrodynamic model for the spawning grounds, simulating the hydrodynamic conditions within the spawning grounds during the peak spawning period of these fish in normal water years. We combined the riverbed bottom measurement results with the suitability curves of various habitat indicators for these fish to establish a habitat suitability model to evaluate fish habitats, such as Figure 4 shown.

[0100] Excavation and dredging are carried out in the areas where siltation has seriously occupied the river channel, while the meandering of the river channel is appropriately maintained. A total of four excavation areas are set up at the upper and lower bends of the fish spawning ground, namely areas ① and ② on the upstream concave bank and convex bank, and areas ③ and ④ on the downstream convex bank. Figure 5 The excavation depth of areas ① and ② is about 4.5m-5.0m, and the excavation depth of areas ③ and ④ is about 4.0m-4.5m. After excavation, the flow area of ​​the river channel is increased, the hydrodynamic habitat conditions of the original narrow section of the river are improved, and a certain degree of river meandering is still retained.

[0101] In the two curved river sections of the fish spawning ground, diversion spur dikes are arranged to improve the single hydrodynamic conditions and unstable river banks, and further create a suitable habitat for fish spawning. The spur dikes are non-submerged, such as Figure 6 Based on experience in the placement of diversion spur dikes, the upstream spur dike has an inflow length of 22.0 meters, representing approximately 29.2% of the total river width. The upstream side of the spur dike forms a 30° angle with the riverbank, while the downstream side forms a 60° angle. The downstream spur dike has an inflow length of approximately 24.0 meters, representing approximately 29.7% of the total river width. The upstream side of the spur dike forms a 30° angle with the riverbank, while the downstream side forms a 60° angle. The two diversion spur dikes are approximately 104 meters apart, approximately 4.5 times the average inflow length of the two dikes.

[0102] By constructing a riverbed habitat evolution model, a six-month simulation of the riverbed evolution was conducted for both the spawning grounds with and without diversion spurs. The impact of diversion spurs on river scouring and sedimentation was verified, and areas with relatively mild scouring and sedimentation were identified as riverbed sections for riverbed modification. The initial riverbed sediment distribution was set based on field measurement data. The simulation results are shown in the figure below. Figure 7 It was found that adding diversion spur dikes effectively reduced the degree of topographical change within the fish spawning grounds. Without the spur dike, the topographical sedimentation height from upstream to the center of the spawning grounds exceeded 2.0 meters, and the riverbed changed dramatically. However, with the spur dike, the topographical change became more gradual, with relatively little change near the dike. Sedimentation heights were less than 1.0 meters at the top of the upstream spur dike and in the section near the downstream spur dike.

[0103] According to the results of the topographic evolution simulation of the spawning grounds, the area near the two diversion spur dikes has a relatively small degree of topographic evolution and can be used as a riverbed modification section. Based on the fish suitability curve for riverbed substrate, 30mm-sized sediment was selected to modify the riverbed. A suitable substrate of approximately 40m long and 10m wide was laid in the central river channel below the top of the upstream diversion spur dike; and a suitable substrate of approximately 140m long and 40m wide was laid in the center of the upstream and downstream diversion spur dikes. Figure 8 .

[0104] This application example uses the restoration measures and time sequence of dredging the river channel, building a diversion spur, and laying appropriate particle size for the spawning ground. In order to evaluate the restoration effect of the invention on the spawning ground habitat, the average flow of the SM River during the fish spawning period (52.7m 3 ·s -1 ) as an example, the water depth, flow velocity and riverbed sediment values ​​in the spawning ground before and after habitat restoration were simulated respectively, and the comprehensive habitat suitability and suitable habitat area of ​​the spawning ground before and after restoration were calculated by combining the fish habitat suitability evaluation model. The results are as follows Figure 9 .

[0105] The simulation results show that the habitat of the spawning grounds has been significantly improved after restoration compared to before restoration. The comprehensive habitat suitability in most river sections exceeds 0.8, and the habitat suitability near the two diversion spur dikes is close to 1.0. The comprehensive habitat suitability of the upstream area with poor original habitat has increased from less than 0.2 to around 0.8. The comprehensive habitat suitability area of ​​the spawning grounds after restoration has increased to 5403m 2 Compared with one year after the dam was demolished, it increased by 86.9%. The effect of the habitat restoration measures of the present invention is significant.

[0106] The above is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that the present invention is susceptible to various modifications and variations. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for restoring fish habitats in mountainous rivers based on numerical simulation optimization, characterized in that: The steps of the method include: Obtain habitat data for mountain river fish habitats and implement preliminary ecological restoration measures for mountain river fish habitats; Construct a numerical simulation model to predict the evolution of scouring and silting of fish habitats in mountain rivers after initial ecological restoration within a set period. Based on the scouring and silting evolution results, identify areas where the degree of scouring and silting evolution within the set period meets a preset threshold; Based on the target fish species, riverbed modifications are carried out in identified areas. Using habitat suitability models, the effects of preliminary ecological restoration measures and riverbed modifications on fish habitat in mountainous rivers are evaluated. Restoration of fish habitat in mountainous rivers is completed based on the evaluation results. The construction of the numerical simulation model specifically includes: Based on numerical simulation, the following models were constructed: hydrodynamic model, sediment transport model and terrain evolution model; coupling a hydrodynamic model, a sediment transport model, and a terrain evolution model to form the numerical simulation model; The specific calculation formula of the sediment transport model is: in, is the sediment transport rate, is the sediment density, is the relative density of sediment, is the critical dimensionless shear stress for sediment initiation, is the median particle size of sediment, In order to consider the hidden exposure coefficient between sediment components, is the dimensionless shear stress of the riverbed, is the water flow velocity, is Xie Cai coefficient, is the efficiency coefficient, is the particle size-related coefficient, The characteristic particle size is that 90% of the sediment is smaller than this particle size.

2. The method for restoring fish habitats in mountainous rivers based on numerical simulation optimization according to claim 1, characterized in that: The initial ecological restoration measures include dredging the sediment accumulation area and constructing a diversion spur dike; The excavation and dredging of the sediment accumulation area is specifically as follows: Excavation is carried out in areas where the hydrodynamic conditions of mountain river fish habitats do not meet the fish habitat requirements, so that the hydrodynamic conditions of mountain river fish habitats are improved after excavation. The hydrodynamic conditions include: water depth of mountain river fish habitats and flow velocity of mountain river fish habitats.

3. The method for restoring fish habitats in mountainous rivers based on numerical simulation optimization according to claim 2, characterized in that: The construction of the diversion spur dike is specifically as follows: One or more spur dikes are constructed at the desired water flow adjustment locations in the fish habitats of mountain rivers, and the length, spacing, height and construction materials of the spur dikes are determined.

4. The method for restoring fish habitats in mountainous rivers based on numerical simulation optimization according to claim 3, characterized in that: The specific calculation formula of the hydrodynamic model is: in, are body-fitting coordinates, is the height of the free surface above the reference plane, is the depth from the reference plane to the river bottom, Represents the total water depth, For time, for The depth-averaged velocity in the direction, for The depth-averaged velocity in the direction, for Coordinate conversion coefficient of direction, for Coordinate conversion coefficient of direction, is the flow change value caused by water inflow and outflow in the calculation unit, and are the source and sink terms of water flow within the calculation unit, is the water density, for The pressure gradient in the direction of for The pressure gradient in the direction of for The turbulent momentum flux in the direction of for η The turbulent momentum flux in the direction of for The momentum source and sink terms in the direction, for The momentum source and sink terms in the direction, is the acceleration due to gravity, is the Xie Cai coefficient of the two-dimensional shallow water equation, for direction of the momentum flux caused by the secondary flow, for Direction of the momentum flux caused by the secondary flow.

5. The method for restoring fish habitats in mountainous rivers based on numerical simulation optimization according to claim 4, characterized in that: The specific calculation formula of the terrain evolution model is: in, is the sediment porosity, is the change in riverbed elevation, is the geomorphic acceleration factor, 、 are the sediment transport amounts per unit width along the x and y directions, respectively.

6. The method for restoring fish habitats in mountainous rivers based on numerical simulation optimization according to claim 5, characterized in that: The numerical simulation model is constructed to predict the evolution of scouring and silting of fish habitats in restored mountain rivers within a set period, specifically: The river topography and hydrological conditions after the implementation of preliminary ecological restoration measures are used as input, and simulation calculations are performed through a coupled numerical simulation model. The scouring and deposition thickness or elevation changes at each point on the riverbed at the end of the set period are output to characterize the scouring and deposition evolution results.

7. The method for restoring fish habitats in mountainous rivers based on numerical simulation optimization according to claim 6, characterized in that: The specific calculation formula of the habitat suitability model is: in, 、 and are the habitat suitability indices of water depth, flow velocity and riverbed sediment in the ith grid in the simulation area; is the comprehensive habitat fitness index of the i-th grid, is the area of ​​the i-th grid, is the weighted effective habitat area, and n is the total number of grids in the simulation area.

8. The method for restoring fish habitats in mountainous rivers based on numerical simulation optimization according to claim 7, characterized in that: The habitat suitability model is used to evaluate the improvement effect of fish habitat in mountain rivers under the combined effects of preliminary ecological restoration measures and riverbed modification, specifically: Obtain data on water depth, flow velocity distribution, and riverbed type in mountain river fish habitats after preliminary ecological restoration measures and riverbed modification; Based on the habitat suitability curve of target fish for water depth, flow velocity and riverbed type data, the habitat suitability index of each evaluation unit is calculated; The comprehensive habitat suitability index of each evaluation unit was calculated by multi-factor combination method; Calculate the weighted effective habitat area of ​​the entire restoration area; The HSI and WUA calculated after the repair are compared with the corresponding values ​​before the repair to obtain the evaluation results.

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