Method for repairing fish habitat in mountain river based on numerical simulation optimization

Abstract

The invention relates to the technical field of mountainous river fish habitat habitat restoration, and relates to a mountainous river fish habitat restoration method based on numerical simulation optimization, comprising: acquiring habitat data of a mountainous river fish habitat, and performing preliminary ecological restoration measures on the mountainous river fish habitat; constructing a numerical simulation model to predict the erosion and deposition evolution result of the fish habitat in the mountain river after the preliminary ecological restoration in a set period, and identifying an area of which the erosion and deposition evolution degree meets a preset threshold value in the set period; and carrying out riverbed substrate transformation on the identified area based on the target fish, evaluating the habitat improvement effect under the combined action of the preliminary ecological restoration measure and the riverbed substrate transformation through a habitat suitability model, and completing the restoration of the fish habitat in the mountain river based on the evaluation result. According to the method, dredging, spur dike and substrate transformation are combined, and numerical simulation optimization is combined, so that the effectiveness, continuity and scientificity of restoration of the fish habitat in the mountain river are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of habitat restoration of mountain river fish habitats. Specifically, it relates to a method for restoring mountain river fish habitats optimized based on numerical simulation. Background Art

[0002] Due to its unique topography and landforms, such as high and steep terrain and complex topography, mountain rivers form river channel characteristics of large slope and high sinuosity. Their riverbed substrates are often mainly composed of primary bedrock, pebbles and coarse sand. Hydrologically, they are characterized by significant seasonal differences in flow and rapid rise and fall of floods. This unique natural environment has given birth to diverse habitat types such as rapids, shoals, deep pools and rich riparian vegetation areas, providing valuable habitats and breeding grounds for many fish species, especially rare fish species, and is an important ecological corridor for maintaining regional biodiversity. However, with the intensification of human activities such as the construction of water conservancy projects, sand mining operations in the river channel and other forms of river channel transformation, the fish habitats in mountain rivers are facing the severe challenges of being massively occupied and severely damaged, directly causing significant adverse effects on the reproduction and survival of river fish populations. At present, in the practice of fish habitat restoration, on the one hand, existing restoration measures such as demolishing some river-blocking facilities, adjusting the local morphology of the river channel or carrying out biological restoration often lack systematic consideration of the specific hydrological, geomorphic and ecological characteristics of mountain rivers, resulting in insufficient universality and pertinence of the restoration plan. On the other hand, the large slope and high sinuosity unique to mountain rivers make the law of water and sediment transport and the process of riverbed evolution extremely complex. At present, the planning and design of habitat restoration measures and the selection of implementation areas rely more on empirical judgment and fail to fully combine the dynamic process of river water and sediment movement for scientific demonstration. This not only makes it difficult to guarantee the long-term sustainability of the restoration results, but also easily leads to poor restoration effects or even negative impacts due to insufficient prediction of complex riverbed evolution. Summary of the Invention

[0003] The purpose of the present invention is to provide a method for restoring mountain river fish habitats optimized based on numerical simulation, which systematically improves the effectiveness, sustainability and scientificity of mountain river fish habitat restoration through the combination of dredging, spur dikes and substrate transformation, and combines numerical simulation optimization, providing a new solution for the protection of rare fish species.

[0004] The present invention is achieved through the following technical solutions: A method for restoring mountain river fish habitats optimized based on numerical simulation, the steps of the method include: Obtain the habitat data of mountain river fish habitats, and perform preliminary ecological restoration measures such as river channel dredging and building deflecting spur dikes on mountain river fish habitats; Build a numerical simulation model to predict the scouring and silting evolution results of the repaired mountain river fish habitat within a set period. According to the scouring and silting evolution results, identify the areas where the degree of scouring and silting evolution meets the preset threshold within the set period; Based on the habitat requirements of target fish, transform the riverbed substrate of the identified areas. Through the habitat suitability model, evaluate the improvement effect of the mountain river fish habitat under the combined action of the preliminary ecological restoration measures and the riverbed substrate transformation, and complete the restoration of the mountain river fish habitat based on the evaluation results.

[0005] Optionally, the preliminary ecological restoration measures include excavating and dredging the sediment deposition areas and constructing spur dikes; Among them, the specific operation of excavating and dredging the sediment deposition areas is as follows: Excavate the areas where the hydrodynamic conditions of the mountain river fish habitat do not meet the habitat requirements of fish, so that the hydrodynamic conditions of the mountain river fish habitat after excavation are improved. Among them, the hydrodynamic conditions include the water depth and flow velocity of the mountain river fish habitat, and the range of hydrodynamic conditions for the habitat requirements of fish varies according to different fish species.

[0006] Optionally, the specific operation of constructing spur dikes is as follows: Build one or more spur dikes at the positions where the water flow needs to be adjusted in the mountain river fish habitat, and determine the length, spacing, height and building materials of the spur dikes.

[0007] Optionally, the construction of the numerical simulation model specifically includes: Based on numerical simulation, respectively build a hydrodynamic model, a sediment transport model and a terrain evolution model; Couple the hydrodynamic model, the sediment transport model and the terrain evolution model to form the numerical simulation model.

[0008] Optionally, the specific calculation formula of the hydrodynamic model is:

[0009]

[0010]

[0011]

[0012]

[0013]

[0014] Among them, is the body-fitted 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, is time, is the depth-averaged flow velocity in the is the depth-averaged flow velocity in the is the coordinate transformation coefficient in the is the coordinate transformation coefficient in the is the value of the flow rate change caused by the inflow and outflow of water in the calculation unit, and are the water flow source term and sink term in the calculation unit respectively, is the water body density, is the pressure gradient in the is the pressure gradient in the is the turbulent momentum flux in the is η the turbulent momentum flux in the is the momentum source and sink term in the is the momentum source and sink term in the is the gravitational acceleration, is the Chezy coefficient of the two-dimensional shallow water equation, is the momentum flux caused by the secondary flow in the is the momentum flux caused by the secondary flow in the

[0015] Optionally, for the sediment transport model, its specific calculation formula is:

[0016]

[0017]

[0018]

[0019] Wherein, is the sediment transport rate, is the sediment density, is the relative density of the sediment, is the critical non-dimensional shear stress for sediment incipient motion, is the median grain size of the sediment, To consider the hidden exposure coefficient between sediment components, is the dimensionless shear stress of the riverbed, is the water flow velocity, is the Chezy coefficient, is the efficiency coefficient, is the Chezy coefficient related to the particle size, is the characteristic particle size at which 90% of the sediment is smaller than this size.

[0020] Optionally, for the terrain evolution model, its specific calculation formula is:

[0021] where, is the sediment porosity, is the change in riverbed elevation, is the geomorphic acceleration factor, , are the sediment transport amounts in the x and y directions per unit width respectively.

[0022] Optionally, for the constructed numerical simulation model to predict the erosion and deposition evolution results of the restored mountain river fish habitat within a set period, specifically: Take the riverbed topography and hydrological conditions after implementing the preliminary ecological restoration measures as inputs, perform simulation operations through the coupled numerical simulation model, and output the erosion and deposition thickness or elevation change of each point on the riverbed at the end of the set period to characterize the erosion and deposition evolution results.

[0023] Optionally, for the habitat suitability model, its specific calculation formula is:

[0024]

[0025] where, , and are the habitat suitability indices of water depth, flow velocity, and riverbed substrate for the i-th grid in the simulation area respectively; is the comprehensive habitat suitability index for 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.

[0026] Optionally, for evaluating the improvement effect of the mountain river fish habitat under the combined action of the preliminary ecological restoration measures and the riverbed substrate transformation through the habitat suitability model, specifically: Obtain the data of water depth, flow velocity distribution, and riverbed substrate type of the mountain river fish habitat after the preliminary ecological restoration measures and the riverbed substrate transformation; Based on the habitat suitability curves of target fish species with respect to water depth, flow velocity, and riverbed substrate type data, calculate the habitat suitability index for each evaluation unit; Calculate the comprehensive habitat suitability index for each evaluation unit through the multi-factor combination method; Calculate the weighted effective habitat area of the entire restoration area; Compare the HSI and WUA calculated after restoration with the corresponding values before restoration to obtain the evaluation results.

[0027] The technical solution of the present invention has at least the following advantages and beneficial effects: The present invention fully considers the geomorphic and hydrological characteristics of mountain rivers, such as high slope drop and strong disturbance, and systematically proposes a combined fish habitat restoration measure of "dredging the river channel - constructing spur dikes - optimizing the laying of suitable substrates" and a scientific implementation sequence. It can not only effectively improve the adverse flow conditions caused by sediment deposition, but also regulate water and sediment through spur dikes, maintain the dredging effect, and create a hydrodynamic environment preferred by fish. Combined with substrate transformation, it comprehensively improves the habitat quality. Its restoration effect is more significant and lasting than single measures, 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 applies numerical simulation technology throughout the entire process of restoration plan design, implementation, and evaluation. By constructing a water and sediment mathematical model to accurately predict riverbed evolution, the best location and timing for substrate transformation are selected, which not only greatly improves the pertinence and effectiveness of restoration measures, ensures the long-term stability and sustainability of restoration results, but also significantly reduces the trial-and-error cost of restoration projects, providing a scientific basis for the quantitative evaluation of restoration effects. More importantly, the present invention always takes the actual habitat needs of target fish species as the core orientation, and the proposed restoration measures and parameters can be flexibly adjusted according to the biological characteristics and habitat preferences of different protected fish species, with high operability and wide applicability, providing important technical support for ecological restoration projects of various mountain rivers, and providing a highly valuable scientific plan and engineering practice guidance for how to successfully create and maintain alternative habitats in tributaries under the current background of hydropower development. Description of the Drawings

[0028] Figure 1 It is a flow chart of the method for restoring fish habitats in mountain rivers optimized based on numerical simulation provided by the present invention; Figure 2 It is a topographic map of the river channel where the spawning ground of the SM River, where the specific implementation case provided by the present invention is located, and a schematic diagram of the spawning ground on site; Figure 3 It is a schematic diagram of the suitability curves of representative fish species in a certain mountain river for each important habitat factor of the river; Figure 4Schematic diagram of the current situation of fish habitat suitability before the habitat restoration of the spawning ground section of the SM River provided by the present invention; Figure 5 Schematic diagram of the comparison of the riverbed topography before and after the dredging project is implemented in the river section of the spawning ground of the SM River provided by the present invention; Figure 6 Schematic diagram of the layout of spur dikes in the river section of the spawning ground of the SM River provided by the present invention; Figure 7 Schematic diagram of the comparison of the topographic evolution in the river section 6 months after the spur dikes are arranged or not in the spawning ground of the SM River provided by the present invention; Figure 8 Schematic diagram of the substrate transformation area and transformation method in the spawning ground of the SM River provided by the present invention; Figure 9 Schematic diagram of the comparison of fish habitat suitability with or without habitat restoration measures in the river section of the spawning ground of the SM River provided by the present invention. Detailed implementation manners

[0029] To make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions in the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the present invention. Obviously, what is described is a part of the present invention, rather than all of it. Usually, the components of the present invention described and illustrated in the accompanying drawings here can be arranged and designed in various different configurations.

[0030] As Figure 1 shown, the present invention provides one of the embodiments: a method for restoring fish habitats in mountain rivers optimized based on numerical simulation, and the steps of the method include: Obtain the habitat data of fish habitats in mountain rivers, and perform preliminary ecological restoration measures on the fish habitats in mountain rivers; Construct a numerical simulation model to predict the scouring and silting evolution results of the fish habitats in mountain rivers restored by the preliminary ecological restoration measures within a set period, and identify the areas where the scouring and silting evolution degree meets the preset threshold within the set period according to the scouring and silting evolution results; Based on the habitat requirements of target fish, transform the riverbed substrate of the identified areas, evaluate the improvement effect of the fish habitats in mountain rivers under the combined action of the preliminary ecological restoration measures and the riverbed substrate transformation through a habitat suitability model, and complete the restoration of the fish habitats in mountain rivers based on the evaluation results.

[0031] In this embodiment, the present invention gradually improves the habitat conditions of mountain river fish by excavating the silted river channel, arranging spur dikes, and transforming the riverbed substrate at appropriate positions. The main steps are as follows: (1) Conduct on-site surveys of the river channel topography and substrate conditions of the fish habitat, establish a mathematical model to simulate important fish habitat indicators such as river channel flow velocity and water depth within the fish habitat, and evaluate the current habitat status according to the fish habitat suitability model. (2) In response to the narrowing of some river channels caused by sediment deposition, which results in water flow conditions unfavorable for fish activities, adopt the method of excavating the riverbed to dredge the river channel, so as to increase the river channel cross-sectional area and improve the water flow conditions within the habitat. (3) According to the river channel form and sediment deposition characteristics, select suitable river sections to construct spur dikes to adjust the water flow direction and sediment transport law, strengthen the main river channel and slow down sediment deposition, and then shape the river geomorphology and hydrodynamic conditions preferred by fish. Based on existing research results, the layout principles of spur dikes are as follows: Spur dike groups are usually arranged crosswise along both banks of the river channel to induce the main flow to take a curved form and adjust the sediment transport law. Research shows that in small rivers or streams, the distance from the top of the spur dike to the opposite bank should be about 70% - 80% of the original river channel width, that is, the length of the dike body should not exceed 30% of the river width. Researchers studied the influence of the interval between spur dikes on the effect of river ecological restoration through numerical simulation. The results show that when the interval between spur dikes is 4 times the dike length, the suitable habitat area is the largest and the ecological restoration effect is the best. The angle between the upstream surface of the spur dike and the river bank is generally about 30° to guide the water flow to the central river channel at an appropriate flow velocity; the angle between the downstream surface and the river bank is generally about 60°, thereby protecting the river bank on this side from being scoured by the water flow. (4) Construct a water and sediment transport and riverbed evolution model for the habitat river section, simulate the process of riverbed erosion and deposition within the habitat under natural incoming flow, select river sections with relatively gentle erosion and deposition phenomena, and transform the riverbed substrate according to the fish living habits to further create a suitable habitat for fish. (5) Use the habitat suitability model to simulate the fish habitat suitability before and after the restoration of the habitat river section, and compare and evaluate the actual effect of the habitat restoration measures.

[0032] In the 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.

[0033] The river channel boundary of mountain rivers has the characteristics of complex curvature. It is difficult to smoothly fit the rectangular grid to the river channel boundary, which may lead to large discretization errors during the calculation process. Therefore, in the horizontal direction, the model selects an orthogonal curvilinear grid to make the grid fit the river channel boundary as smoothly as possible. The corresponding coordinate system selects an orthogonal curvilinear coordinate system ( ξ , η ), that is, the body-fitted coordinate, and its conversion with the rectangular coordinate (x, y) is completed through the conversion coefficients and .

[0034] The description of each model equation is as follows: Continuity equation of the hydrodynamic model:

[0035] Wherein, is the height of the free surface above the reference plane z = 0, with the unit of m, is the depth from the reference plane to the river bottom, with the unit of m, is the total water depth, is the time, is the depth-averaged velocity in the is the depth-averaged velocity in the -1 , is the coordinate transformation coefficient in the is the coordinate transformation coefficient in the and The expressions of

[0036]

[0037] is the value of the flow rate change caused by the inflow and outflow of water in the calculation unit, with the unit of m 3 ·s -1 :

[0038] Wherein, and are respectively the water source term and sink term in the calculation unit, with the unit of 1·s -1 , in this embodiment, the model established does not consider rainfall and evaporation, so is only related to and .

[0039] Momentum equation of the hydrodynamic model: The depth-averaged momentum equations in the and

[0040]

[0041] Wherein, is the water body density, with the unit of kg·m -3 , is the pressure gradient in the-2 ·s -2 , is the pressure gradient in the is the turbulent momentum flux in the direction, unit m·s -2 , is η the turbulent momentum flux in the direction is the momentum source / sink term in the direction is the momentum source / sink term in the direction, unit m·s -2 , is the acceleration due to gravity is the Chezy coefficient of the two-dimensional shallow water equation, unit m 1 / 2 ·s -1 , is the momentum flux caused by secondary flow in the direction is the momentum flux caused by secondary flow in the direction, unit m·s -2 . The hydrodynamic model, the hydrodynamic boundary conditions include the flow rate at the inflow boundary and the water level at the outflow boundary. The inflow boundary flow rate process is: the flow rate process in a normal water year of the study reach, measured by a hydrological station, and the downstream water level is obtained by extrapolating the flow rate - water level curve of the cross-section where it is located.

[0042] Sediment transport model, in the process of river sediment transport, the expression of the sediment transport rate S is:

[0043] where is the sediment transport rate is the sediment density, unit kg·m -3 , is the relative density of sediment is the critical non-dimensional shear stress for sediment incipient motion, here it is 0.047 is the median sediment diameter is the hiding and exposure coefficient considering the sediment components is the non-dimensional shear stress of the riverbed, and its specific form is:

[0044] where is the water flow velocity, unit m·s -1 , is the Chezy coefficient, unit m 1 / 2 ·s -1 , is the efficiency coefficient, and its specific form is:

[0045] Among them, is the Chezy coefficient related to the particle size, and its calculation formula is:

[0046] Among them, is 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 of the normal water year of the hydrological station in the river section where it is located are selected.

[0047] For the terrain evolution model, in the model calculation, the riverbed terrain will be dynamically updated in each calculation time step, and subsequently, the change of the terrain will also affect the calculation of the hydrodynamic conditions. After each calculation time step, the riverbed elevation is updated using the Exner equation based on the sediment mass conservation, and the expression of the Exner equation is as follows:

[0048] Among them, is the sediment porosity, which is set to 0.4, is the change amount of the riverbed elevation, with the unit of m, is the geomorphic acceleration factor, and are the sediment transport amounts along the x and y directions per unit width respectively, with the unit of kg·m -1 ·s -1 .

[0049] For the habitat suitability model, a fish habitat suitability evaluation model is established by combining the simulation results of the hydrodynamic, sediment transport and terrain evolution models and the suitability curves of fish for habitat indicators such as hydrodynamic conditions and substrate. The fish habitat suitability curve is a curve established based on the physiological and behavioral responses of fish to various habitat indicators to describe the survival and reproduction abilities of fish under different environmental conditions, and is defined by a value between 0 and 1 to indicate the preference degree of fish for a single habitat factor. 0 indicates no preference for specific key habitat elements, and 1 indicates the maximum preference for key habitat elements.

[0050] According to the simulation results of each habitat indicator in the simulation area, combined with the fish suitability curve, calculate the suitability index SI (Suitability Index) of each habitat indicator in each grid in the simulation area. Subsequently, 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 reach.

[0051] In this embodiment, water depth, flow velocity, and riverbed sediment particle size are selected as the key habitat indicators for evaluating the habitat suitability of the dam removal reach, and the suitability index SI of each indicator is calculated through the fish habitat suitability curve. The calculation formulas for the habitat suitability index HSI and the weighted effective habitat area WUA are as follows:

[0052]

[0053] Among them, 、 and are the habitat suitability indices of water depth, flow velocity, and riverbed sediment in the i-th grid of the simulation area, respectively; is the comprehensive habitat suitability index of the i-th grid, is the area of the i-th grid, with the unit of m 2 , is the weighted effective habitat area, and n is the total number of grids in the simulation area. By comparing the results of the river habitat survey, the measurement standard of the comprehensive habitat suitability index HSI is tested. The results show that the habitat in the area where HSI≥0.8 is relatively good, and the suitability level is highly suitable; when 0.8>HSI≥0.6, the suitability level is suitable, and when HSI<0.2, the regional habitat is poor, and the suitability level is unsuitable.

[0054] In this embodiment, an application example is also provided: The application example is selected as the fish spawning ground on the first-class tributary SM River of a large river in the southwestern mountainous area of China. Specifically, as shown in Figure 2 Taking the representative fish of a mountain river as the target fish, specifically as shown in Figure 3 The spawning peak period of this fish is in September, and its habitat suitability curves for water depth, flow velocity, and riverbed substrate are as shown in Figure 3 .

[0055] The specific operation steps of the entire application example are as follows: As shown in Figure 2 , measure the terrain and substrate conditions of the reach where the fish spawning ground is located on-site, collect the hydrological data of the SM River Basin for many years to calculate the normal water year of the river. Establish a hydrodynamic model for the spawning ground reach to simulate the hydrodynamic conditions in the spawning ground during the spawning peak period of this fish in the normal water year. Combine the riverbed sediment measurement results with the habitat suitability curves of this fish for each habitat indicator to establish a habitat suitability model to evaluate the fish habitat, as shown in Figure 4 .

[0056] Excavate and dredge the areas in the spawning ground where siltation seriously occupies the river channel, and at the same time appropriately maintain the meandering of the river channel. A total of 4 excavation areas are set at the two bends above and below the fish spawning ground, namely areas ① and ② at the upstream concave bank and convex bank, and areas ③ and ④ at the downstream convex bank, as shown in 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 cross-sectional area of the river channel increases, the hydrodynamic habitat conditions of the original constricted river section are improved, and a certain degree of river channel meandering is still retained.

[0057] Build spur dikes in the two curved river sections within the fish spawning ground to improve problems such as single hydrodynamic conditions and unstable riverbanks, and further create a suitable spawning habitat for fish. The type of spur dike is non-submerged, such as Figure 6 . According to the layout experience of the spur dike group, the length of the upstream spur dike entering the river is 22.0m, accounting for about 29.2% of the total river width. The angle between the upstream surface of the spur dike and the riverbank is 30°, and the angle between the downstream surface and the riverbank is about 60°; the length of the downstream spur dike entering the river is about 24.0m, accounting for about 29.7% of the total river width. The angle between the upstream surface of the spur dike and the riverbank is 30°, and the angle between the downstream surface and the riverbank is about 60°. The distance between the two flow-regulating spur dikes is about 104m, approximately 4.5 times the average length of the two spur dikes entering the river.

[0058] By constructing a riverbed habitat evolution model, conduct a 6-month simulation of water and sediment transport and riverbed evolution with and without spur dikes in the spawning ground to verify the impact of spur dikes on river erosion and deposition, and find the areas with relatively gentle erosion and deposition in the river section as the riverbed sediment transformation sections. The initial distribution of riverbed sediment is set according to on-site measured data. The simulation results are as shown in Figure 7 . It can be found that building spur dikes can effectively reduce the degree of topographic evolution in the river channel of the fish spawning ground. Without spur dikes, the height of sediment deposition in the central river channel from the upstream to the middle reaches of the spawning ground exceeds 2.0m, and the riverbed evolution is relatively intense; while after building spur dikes, the geomorphic evolution is more gentle, and the degree of geomorphic evolution near the spur dikes is relatively small. The sediment deposition height at the top of the upstream spur dike and near the downstream spur dike is less than 1.0m.

[0059] According to the simulation results of the topographic evolution of the spawning ground river section, the degree of topographic evolution in the areas near the two spur dikes is relatively small, which can be used as the riverbed sediment transformation sections. According to the suitability curve of fish for riverbed sediment, choose to lay sediment with a particle size of 30mm to transform the riverbed. Lay suitable sediment with a length of about 40m and a width of about 10m in the central river channel below the top of the upstream spur dike; lay suitable sediment with a length of about 140m and a width of about 40m in the central part upstream and downstream of the downstream spur dike, such as Figure 8 .

[0060] In this application example, through the habitat restoration measures and time sequence of dredging the river channel - constructing spur dikes - laying spawning grounds with appropriate particle sizes, in order to evaluate the restoration effect of the present invention on the spawning ground habitat, taking the average flow rate (52.7 m 3 ·s -1 ) of the SM River during the peak fish spawning period as an example, the values of water depth, flow velocity and riverbed substrate in the spawning ground reach before and after habitat restoration are respectively simulated. Combining with the fish habitat suitability evaluation model, the comprehensive habitat suitability and suitable habitat area of the spawning ground before and after restoration are calculated. The results are as Figure 9 .

[0061] The simulation results show that the habitat in the spawning ground after restoration has been significantly improved compared with that before restoration. The comprehensive habitat suitability in most reaches exceeds 0.8, and the habitat suitability near the two spur dikes is close to 1.0; the comprehensive habitat suitability in the area with poor original habitat in the upper reaches has increased from less than 0.2 to around 0.8. The suitable area of the comprehensive habitat of the spawning ground after restoration has increased to 5403 m 2 , which is 86.9% higher than that one year after the dam removal. The effect of the habitat restoration measures of the present invention is significant.

[0062] The above is only a preference of the present invention and is not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for restoring fish habitats in mountain rivers optimized based on numerical simulation, characterized in that The steps of the method include: Obtain the habitat data of mountain river fish habitats and implement preliminary ecological restoration measures for mountain river fish habitats; Construct a numerical simulation model to predict the erosion and deposition evolution results of the mountain river fish habitats after preliminary ecological restoration within a set period. According to the erosion and deposition evolution results, identify the areas where the erosion and deposition evolution degree meets the preset threshold within the set period; Based on the target fish, transform the riverbed substrate of the identified areas. Through the habitat suitability model, evaluate the improvement effect of the mountain river fish habitats under the combined action of the preliminary ecological restoration measures and the riverbed substrate transformation. Complete the restoration of the mountain river fish habitats based on the evaluation results.

2. The method for restoring fish habitats in mountain rivers optimized based on numerical simulation according to claim 1, characterized in that The preliminary ecological restoration measures include excavating and dredging the sediment deposition areas and constructing spur dikes; Among them, the specific implementation of the excavation and dredging of the sediment deposition areas is as follows: Excavate the areas where the hydrodynamic conditions of the mountain river fish habitats do not meet the fish habitat requirements, so that the hydrodynamic conditions of the mountain river fish habitats after excavation are improved. Among them, the hydrodynamic conditions include: the water depth of the mountain river fish habitats and the flow velocity of the mountain river fish habitats.

3. The method for restoring fish habitats in mountain rivers optimized based on numerical simulation according to claim 2, wherein, The specific implementation of the construction of spur dikes is as follows: Build one or more spur dikes at the positions where the water flow needs to be adjusted in the mountain river fish habitats, and determine the length, spacing, height and building materials of the spur dikes.

4. The method for restoring fish habitats in mountain rivers optimized based on numerical simulation according to claim 3, characterized in that, The specific construction of the numerical simulation model includes: Based on numerical simulation, respectively construct: a hydrodynamic model, a sediment transport model and a terrain evolution model; Couple the hydrodynamic model, the sediment transport model and the terrain evolution model to form the numerical simulation model.

5. The method for restoring fish habitats in mountain rivers optimized based on numerical simulation according to claim 4, characterized in that, The specific calculation formula of the hydrodynamic model is: Among them, is the body-fitted 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, is the time, is the depth-averaged velocity in the direction, is the depth-averaged velocity in the direction, is the coordinate transformation coefficient in the direction, and are respectively the source term and sink term of the water flow in the calculation unit, is the density of the water body, is the pressure gradient in the direction, is the pressure gradient in the direction, is η the turbulent momentum flux in the direction, is the turbulent momentum flux in the direction, is the gravitational acceleration, is the Chezy coefficient of the two-dimensional shallow water equation, is the momentum flux caused by the secondary flow in the direction, is the momentum flux caused by the secondary flow in the direction.

6. The method for restoring fish habitats in mountain rivers optimized based on numerical simulation according to claim 5, wherein The specific calculation formula of the sediment transport model is: Among them, is the sediment transport rate, is the sediment density, is the relative density of the sediment, is the critical non - dimensional shear stress for sediment incipient motion, is the median sediment diameter, is the hiding - exposure coefficient considering the sediment components, is the non - dimensional shear stress of the riverbed, is the water flow velocity, is the Chezy coefficient, is the efficiency coefficient, is the Chezy coefficient related to the particle size, is the characteristic particle size at which 90% of the sediment is smaller than this size.

7. The method for restoring fish habitats in mountain rivers optimized based on numerical simulation according to claim 6, characterized in that, The specific calculation formula of the terrain evolution model is: wherein, is the sediment porosity, is the change in riverbed elevation, is the geomorphic acceleration factor, and are the sediment transport rates per unit width in the x and y directions, respectively.

8. The method for restoring fish habitats in mountain rivers optimized based on numerical simulation according to claim 7, characterized in that The specific implementation of constructing the numerical simulation model to predict the erosion and deposition evolution results of the restored mountain river fish habitats within a set period is as follows: Take the river channel terrain and hydrological conditions after the implementation of the preliminary ecological restoration measures as inputs, and perform simulation operations through the coupled numerical simulation model, and output the erosion and deposition thickness or elevation change of each point on the riverbed at the end of the set period to characterize the erosion and deposition evolution results.

9. The method for restoring fish habitats in mountain rivers optimized based on numerical simulation according to claim 8, characterized in that, The specific calculation formula of the habitat suitability model is: Among them, , and are the habitat suitability indices of water depth, flow velocity, and riverbed substrate of the i-th grid in the simulation area, respectively; is the comprehensive habitat suitability 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.

10. The method for restoring fish habitats in mountain rivers optimized based on numerical simulation according to claim 9, characterized in that, The specific implementation of evaluating the improvement effect of the mountain river fish habitats under the combined action of the preliminary ecological restoration measures and the riverbed substrate transformation through the habitat suitability model is as follows: Obtain the water depth, flow velocity distribution and riverbed substrate type data of the mountain river fish habitats after the preliminary ecological restoration measures and the riverbed substrate transformation; Based on the habitat suitability curves of the target fish for the water depth, flow velocity and riverbed substrate type data, calculate the habitat suitability index of each evaluation unit; Calculate the comprehensive habitat suitability index of each evaluation unit through the multi-factor combination method; Calculate the weighted effective habitat area of the entire restoration area; Compare the calculated HSI and WUA after restoration with the corresponding values before restoration to obtain the evaluation results.

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