River fish habitat restoration method based on step dam dismantling

Abstract

The invention relates to the technical field of fish habitat treatment, in particular to a river fish habitat restoration method based on stair dam dismantling, which comprises the following steps: acquiring stair dam parameters, hydrological data and fish habitat demand data of a target river; constructing a habitat suitability curve, a habitat suitability index and an effective habitat area model of the fish habitat before dam dismantling; designing a plurality of groups of stair dam dismantling schemes, and simulating hydrological condition changes after dam dismantling in combination with a hydrodynamic model; according to the method, habitat suitability curves, a weighted available area method and river connectivity indexes under different dam dismantling schemes are calculated, a multi-objective optimization model is established to screen an optimal scheme, ecological benefits and engineering cost are comprehensively considered, the optimal dam dismantling scheme can be scientifically selected, a dam body with the maximum contribution to improvement of the ecological benefits is preferentially dismantled, and the dam dismantling efficiency is improved. And meanwhile, part of the dam foundation is reserved to reduce the influence of sediment discharge on the downstream, so that the engineering cost is reduced to the maximum extent while the ecological restoration target is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of fish habitat governance, in particular to a method for restoring river fish habitats based on the removal of cascade dams. Background Art

[0002] Fish habitat restoration, as a core topic in the cross - field of water conservancy projects and ecological protection, currently mainly relies on means such as artificial fish stocking, fish - passing facilities construction, and local habitat transformation. Artificial fish stocking alleviates population decline by supplementing fry, but it is difficult to solve the problem of gene diversity loss caused by habitat fragmentation, and may exacerbate ecological imbalance due to artificial intervention. Although fish - passing facilities (such as fish ladders and fish elevators) are designed to restore fish migration channels, their designs often deviate from the behavior patterns of target fish, and their operation and maintenance costs are high, with an actual passing efficiency of less than 30%. Local habitat transformation technologies (such as artificial fish nests and groynes) can improve the specific water environment, but lack a systematic analysis of the whole - basin hydrological - ecological coupling mechanism, resulting in fragmented restoration effects.

[0003] Existing restoration methods generally rely on qualitative experience judgment and lack quantitative analysis tools based on hydrodynamic models and habitat suitability indicators. For example, cascade dam removal plans mostly adopt a "one - size - fits - all" mode, without considering the differential impacts of flow velocity and water depth in different river reaches on fish spawning grounds. At the same time, existing technologies mostly focus on local habitat optimization, ignoring the synergistic improvement mechanism of the longitudinal connectivity (restoration of migration channels) and lateral connectivity (regeneration of floodplain wetlands) of rivers after dam removal, resulting in a mismatch between the restoration effect and the overall needs of the ecosystem. In addition, there is a lack of prediction models for the long - term dynamic impacts of sediment transport, riverbed evolution, etc. on habitat suitability after dam removal, and the sustainability of restoration plans is insufficient.

[0004] The current technical system has not yet broken through the bottleneck of quantitative assessment of multi - scale ecological responses after dam removal, especially with significant short - comings in dynamic prediction of habitat suitability and synergistic optimization of connectivity. Existing research mostly evaluates habitat quality based on static environmental parameters and fails to combine hydrodynamic models to simulate the hydrological regime evolution after dam removal, resulting in restoration plans that cannot accurately match the behavioral needs of fish. In addition, traditional methods lack the ability to dynamically model the coupling relationship between sediment transport - riverbed geomorphology - fish habitat suitability, making it difficult to predict the long - term stability of habitat quality after dam removal. How to construct a multi - objective optimization model that takes into account both ecological benefits and engineering feasibility has become the key challenge to improve the effect of fish habitat restoration. Summary of the Invention

[0005] The purpose of the present invention is to overcome the above - mentioned deficiencies and provide a method for restoring river fish habitats based on the removal of cascade dams to solve the problems raised in the background art.

[0006] To solve the above technical problems, the technical solution adopted by the present invention is: a method for restoring river fish habitats based on cascade dam removal, comprising the following steps:

[0007] S1: Basic data collection and processing;

[0008] S2: Modeling and evaluation of pre-removal habitat suitability;

[0009] S3: Design of dam removal plan and simulation of hydrodynamic model;

[0010] S4: Construction of multi-objective optimization decision-making model;

[0011] S5: Implementation of dynamic restoration measures and verification of effects.

[0012] Preferably, the S1 specifically comprises the following steps:

[0013] S11: Collection of hydrological and topographic data:

[0014] Collect the cascade dam parameters and historical hydrological data of the target river, and use unmanned aerial vehicle (UAV) aerial survey or remote sensing technology to obtain the river channel topographic data to construct a digital elevation model;

[0015] S12: Investigation of fish habitat data:

[0016] Obtain the distribution of spawning grounds and foraging grounds of the target fish and the requirements of key environmental factors through underwater sonar and catch surveys, and establish a species-environment relationship database.

[0017] Preferably, the S2 specifically comprises the following steps:

[0018] S21: Construction of habitat suitability curve:

[0019] Adopt the weighted available area method to calculate the suitability curves of the target fish for flow velocity, water depth, and substrate;

[0020] S22: Calculation of habitat suitability index and effective habitat area:

[0021] Based on the habitat suitability curve and the simulation of pre-removal hydrological conditions by a two-dimensional hydrodynamic model, calculate the spatial distribution of the habitat suitability index and the effective habitat area.

[0022] More preferably, the formula for calculating the suitability curves of the target fish for flow velocity, water depth, and substrate by adopting the weighted available area method in the S21 is:

[0023]

[0024] Where, W i is the environmental factor weight, and S i (X) is the suitability function of each factor.

[0025] More preferably, in S22, based on the habitat suitability curve and the two-dimensional hydrodynamic model to simulate the pre-dam removal hydrological conditions, the formulas for calculating the spatial distribution of the habitat suitability index and the effective habitat area are as follows:

[0026]

[0027] Among them, HSI: habitat suitability index, which is a comprehensive index integrating the suitability of multiple environmental factors and is used to evaluate the quality of fish habitats; WUA: effective habitat area, which refers to the habitat area that fish can utilize under specific environmental conditions and is calculated by the weighted available area method, reflecting the actual available space of fish in different habitats, and A i is the grid cell area.

[0028] Preferably, S3 specifically includes the following steps:

[0029] S31: Generation of dam removal plan combinations:

[0030] Design full removal, partial removal, and staged removal modes, set the removal sequence, and design the ecological operation rules after dam removal in combination with the ecological flow requirements;

[0031] S32: Construction of hydrodynamic-habitat coupling model:

[0032] Based on the hydrodynamic model, simulate the river channel flow, sediment transport, and riverbed evolution processes after dam removal, couple the fish habitat module, and dynamically output the changes in the habitat suitability index and the effective habitat area under different scenarios.

[0033] Preferably, S4 specifically includes the following steps:

[0034] S41: Calculation of the river connectivity index RCI;

[0035] S42: Multi-objective comprehensive evaluation.

[0036] More preferably, S41 is specifically:

[0037] Use the graph theory method to quantify the longitudinal connectivity before and after dam removal, and the formula is:

[0038]

[0039] Among them, L i is the length of the connected river section; C i is the obstacle influence coefficient, which is set to 0 after dam removal; L total is the total length in the ideal state or the research scope.

[0040] More preferably, S42 is specifically:

[0041] Construct the objective function set: maximize the WUA increment, maximize the RCI improvement value, and minimize the dam removal cost;

[0042] Adopt a multi-objective optimization algorithm to screen the Pareto optimal solution set, and determine the final solution through the entropy weight-TOPSIS method;

[0043]

[0044] Among them: ΔWUA is the WUA increment of a certain solution; ΔRCI is the RCI improvement value of a certain solution; C is the total cost of a certain solution; W WUA is the WUA weight; W RCI is the RCI weight; W C is the cost weight. Among them: ΔWUA is the WUA increment of a certain solution; ΔRCI is the RCI improvement value of a certain solution; C is the total cost of a certain solution; W WUA is the WUA weight; ΔWUA MAX is the maximum WUA increment among all solutions; W RCI is the RCI weight; ΔRCI MAX is the maximum RCI improvement value among all solutions; W C is the cost weight; C MIN is the lowest cost among all solutions.

[0045] Preferably, step S5 specifically includes the following steps:

[0046] S51: Implementation of repair measures:

[0047] Demolish the dam according to the preferred plan, and synchronously implement auxiliary repair measures, including reshaping the micro-topography of the river channel, arranging artificial fish nests, and restoring the vegetation in the riparian zone;

[0048] S52: Post-effect monitoring and model iteration:

[0049] Track the fish migration behavior through acoustic tags, verify the improvement effect of the habitat suitability index and the effective habitat area after dam removal, and use the monitoring data to correct the model parameters to form a closed-loop optimization mechanism of "simulation-implementation-feedback".

[0050] Advantages of the present invention:

[0051] 1. The river fish habitat restoration method based on cascade dam removal designed by the present invention can scientifically select the optimal dam removal plan through a multi-objective optimization decision-making model, comprehensively considering ecological benefits and engineering costs. It preferentially removes the dam that contributes the most to the improvement of ecological benefits, and at the same time retains part of the dam foundation to reduce the impact of sediment discharge on the downstream, so as to minimize the engineering cost while achieving the ecological restoration goal.

[0052] 2. By demolishing or partially demolishing cascade dams, the longitudinal connectivity of rivers can be effectively restored, providing unobstructed migration channels for migratory fish so that they can reach spawning and foraging grounds smoothly, thereby promoting the reproduction and survival of fish populations.

[0053] 3. By restoring the natural hydrological processes and ecological connectivity of rivers, the adaptability and resilience of the ecosystem to external pressures such as climate change and human activity disturbances are enhanced, making the river ecosystem more stable and healthy, and promoting the dynamic balance of the ecosystem. This method not only focuses on the restoration of fish habitats, but also improves the structure and function of the entire river ecosystem through measures such as the restoration of riparian zone vegetation, promoting the dynamic balance and sustainable development of the ecosystem. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 It is a schematic diagram of the overall system flow of the present invention;

[0055] Figure 2 It is a schematic diagram of the system flow for basic data collection and processing in the present invention;

[0056] Figure 3 It is a schematic diagram of the system flow for pre-demolition habitat suitability modeling in the present invention;

[0057] Figure 4 It is a schematic diagram of the system flow for dam demolition plan design and hydrodynamic model construction in the present invention;

[0058] Figure 5 It is a schematic diagram of the system flow for constructing a multi-objective optimization decision-making model in the present invention;

[0059] Figure 6 It is a schematic diagram of the system flow for dynamic restoration and effect verification in the present invention;

[0060] Figure 7 It is a schematic diagram of the water flow in the embodiment of the present invention;

[0061] Figure 8 It is a schematic diagram of the flow velocity in the embodiment of the present invention;

[0062] Figure 9 It is a schematic diagram of the automatically generated plan in the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0063] The present invention will be further described in detail below with reference to the drawings and specific embodiments.

[0064] Embodiment 1:

[0065] A method for restoring fish habitats in rivers based on the demolition of cascade dams includes the following steps:

[0066] S1: Basic data collection and processing;

[0067] S2: Modeling and evaluation of pre - demolition habitat suitability;

[0068] S3: Design of dam - removal plan and simulation of hydrodynamic model;

[0069] S4: Construction of multi - objective optimization decision - making model;

[0070] S5: Implementation of dynamic restoration measures and verification of effects.

[0071] Preferably, the S1 specifically includes the following steps:

[0072] S11: Collection of hydrological and topographic data:

[0073] Collect the cascade dam parameters and historical hydrological data of the target river, and use unmanned aerial vehicle (UAV) aerial survey or remote sensing technology to obtain the river channel topographic data and construct a digital elevation model;

[0074] S12: Investigation of fish habitat data:

[0075] Obtain the distribution of spawning grounds and foraging grounds of the target fish and the requirements of key environmental factors through underwater sonar and catch surveys, and establish a species - environment relationship database. In addition, fish habitat data includes the distribution of spawning grounds of the target fish, water depth, flow velocity, and substrate preference threshold, which are obtained through underwater sonar and catch surveys.

[0076] Preferably, the S2 specifically includes the following steps:

[0077] S21: Construction of habitat suitability curve:

[0078] Adopt the weighted available area method to calculate the suitability curves of the target fish for flow velocity, water depth, and substrate; in this embodiment, the construction of the habitat suitability curve adopts the weighted available area method, integrates the suitability functions of flow velocity, water depth, and substrate environmental factors, and verifies the spatial distribution through a two - dimensional hydrodynamic model.

[0079] S22: Calculation of habitat suitability index and effective habitat area:

[0080] Based on the habitat suitability curve and the two - dimensional hydrodynamic model to simulate the pre - demolition hydrological conditions, calculate the spatial distribution of the habitat suitability index and the effective habitat area.

[0081] More preferably, the formula for calculating the suitability curves of the target fish for flow velocity, water depth, and substrate by using the weighted available area method in S21 is:

[0082]

[0083] Where W i is the environmental factor weight, S i(X) is the suitability function of each factor.

[0084] More preferably, in S22, based on the habitat suitability curve and the two-dimensional hydrodynamic model to simulate the pre-dam removal hydrological conditions, the formulas for calculating the spatial distribution of the habitat suitability index and the effective habitat area are as follows:

[0085]

[0086] Among them, HSI: Habitat Suitability Index, which is a comprehensive index integrating the suitability of multiple environmental factors and is used to evaluate the quality of fish habitats; WUA: Effective Habitat Area, which refers to the habitat area that fish can utilize under specific environmental conditions and is calculated by the weighted available area method, reflecting the actual available space of fish in different habitats, and A i is the grid cell area.

[0087] Preferably, S3 specifically includes the following steps:

[0088] S31: Generation of dam removal plan combinations:

[0089] Design full removal, partial removal, and staged removal modes, set the removal order, and design the ecological operation rules after dam removal in combination with the ecological flow requirements;

[0090] S32: Construction of hydrodynamic-habitat coupling model:

[0091] Based on the hydrodynamic model to simulate the post-dam removal river channel flow, sediment transport, and riverbed evolution processes, couple the fish habitat module, and dynamically output the changes in the habitat suitability index and the effective habitat area under different scenarios. In this embodiment, the hydrodynamic model is a dynamic model coupling sediment transport and riverbed evolution, simulating the impacts of post-dam removal river channel flow, water temperature, and sediment on fish habitats.

[0092] Preferably, S4 specifically includes the following steps:

[0093] S41: Calculation of the river connectivity index RCI;

[0094] S42: Multi-objective comprehensive evaluation.

[0095] More preferably, S41 is specifically:

[0096] Using the graph theory method to quantify the longitudinal connectivity before and after dam removal, the formula is:

[0097]

[0098] Among them, L i is the length of the connected river section; C i is the obstacle influence coefficient, which is set to 0 after dam removal; Ltotal The total length of the ideal state or the research scope.

[0099] More preferably, the S42 is specifically:

[0100] Construct an objective function set: maximize the WUA increment, maximize the RCI improvement value, and minimize the dam removal cost;

[0101] Use a multi-objective optimization algorithm to screen the Pareto optimal solution set, and determine the final solution through the entropy weight-TOPSIS method;

[0102]

[0103] Where: ΔWUA is the WUA increment of a certain solution; ΔRCI is the RCI improvement value of a certain solution; C is the total cost of a certain solution; W WUA is the WUA weight; W RCI is the RCI weight; W C is the cost weight, where: ΔWUA is the WUA increment of a certain solution; ΔRCI is the RCI improvement value of a certain solution; C is the total cost of a certain solution; W WUA is the WUA weight; ΔWUA MAX is the maximum WUA increment among all solutions (for example, ΔWUA of solution 7 = 35%); W RCI is the RCI weight; ΔRCI MAX is the maximum RCI improvement value among all solutions (for example, ΔRCI of solution 7 = 0.2); W C is the cost weight; C MIN is the lowest cost among all solutions (for example, the cost of solution 2 = 100% budget).

[0104] Preferably, the S5 specifically includes the following steps:

[0105] S51: Implement repair measures:

[0106] Demolish the dam according to the preferred plan, and synchronously implement auxiliary repair measures, including reshaping the micro-topography of the river channel, arranging artificial fish nests, and restoring the vegetation in the riparian zone; among them, reshaping the micro-topography of the river channel forms a deep pool-shoal sequence.

[0107] S52: Post-effect monitoring and model iteration:

[0108] Track the fish migration behavior through acoustic tags, verify the improvement effect of the habitat suitability index and the effective habitat area after dam removal, and use the monitoring data to correct the model parameters to form a closed-loop optimization mechanism of "simulation-implementation-feedback".

[0109] Example 2:

[0110] Fish habitat restoration refers to a series of measures to restore and improve the environment for fish survival, in order to protect and restore the fish population quantity and diversity, including the following aspects:

[0111] Dam and hydropower station removal: The construction of dams and hydropower stations often changes the natural flow of rivers, leading to the fragmentation of river ecosystems and affecting fish habitats. Removing these facilities can restore the free-flowing state of rivers, thus improving the living environment of fish. For example, Zhaotong City took the initiative to remove 17 small hydropower stations on the Chishui River to restore the connectivity and ecological functions of the river. Habitat restoration: After removing dams and hydropower stations, damaged habitats need to be restored. This includes measures such as constructing backwater beaches and restoring habitats. After removing dams and hydropower stations, damaged habitats need to be restored. This includes measures such as constructing backwater beaches and restoring habitats.

[0112] Cascade dams block fish migration channels, resulting in habitat fragmentation and changes in hydrological regimes. Traditional restoration methods (such as fish ladders and artificial proliferation) are costly and difficult to systematically restore habitat functions. Existing dam removal plans lack quantitative assessments of habitat suitability (HSI, WUA) and river connectivity (RCI), and do not combine hydrodynamic models to predict the habitat evolution process after dam removal. Provide a dynamic optimization method for dam removal plans based on habitat suitability curves (HSC) and river connectivity indices (RCI), and through coupling hydrodynamic models with multi-objective decision-making algorithms, achieve the coordinated improvement of ecological restoration and engineering feasibility.

[0113] A method for restoring river fish habitats based on the removal of cascade dams, the steps of which are as follows:

[0114] S1: Basic data collection and processing;

[0115] S11: Hydrological and topographic data collection;

[0116] Obtain the distribution, dam height, reservoir capacity, and discharge facility parameters of cascade dams on the target river, as well as historical hydrological data (flow velocity, flow rate, water temperature, sediment content);

[0117] Use unmanned aerial vehicle aerial survey or remote sensing technology to obtain river channel topographic data (riverbed elevation, cross-section morphology, substrate type), and construct a digital elevation model (DEM);

[0118] S12: Fish habitat data investigation;

[0119] Determine the distribution of spawning grounds and foraging grounds of target fish (such as migratory fish) and the requirements for key environmental factors (water depth, flow velocity, substrate) through underwater sonar and catch surveys;

[0120] Establish a species-environment relationship database to quantify the suitability thresholds of different fish for each habitat parameter.

[0121] S2: Modeling of Habitat Suitability before Damming

[0122] S21: Construction of Habitat Suitability Curve

[0123] The weighted available area method is used to calculate the suitability curves of target fish for flow velocity, water depth, and substrate. The formula is:

[0124]

[0125] where W i is the weight of environmental factors, and S i (X) is the suitability function of each factor.

[0126] S22: Calculation of Habitat Suitability Index (HSI) and Weighted Usable Area (WUA)

[0127] Based on the HSC and two-dimensional hydrodynamic models (such as MIKE21, HEC-RAS), the pre-dam removal hydrological conditions are simulated, and the spatial distributions of HSI and WUA are calculated. The formula is:

[0128]

[0129] HSI: Habitat Suitability Index, which is a comprehensive index integrating the suitability of multiple environmental factors (such as flow velocity, water depth, substrate), used to evaluate the quality of fish habitats.

[0130] WUA: Weighted Usable Area, which refers to the habitat area that fish can utilize under specific environmental conditions, calculated by the weighted available area method, reflecting the actual available space of fish in different habitats.

[0131] S3: Design of Dam Removal Plan and Construction of Hydrodynamic Model

[0132] S31: Generation of Dam Removal Plan Combinations

[0133] Full removal, partial removal (retaining the dam foundation), staged removal, etc. modes are developed, and the removal sequence (single dam first, multi-dam linkage) is set.

[0134] Combined with the ecological flow requirements, the ecological operation rules after dam removal are designed (such as minimum downstream discharge, pulse flood discharge to simulate natural hydrological rhythms).

[0135] S32: Development of Hydrodynamic-Habitat Coupled Model

[0136] Based on the hydrodynamic model (such as Delft3D), the post-dam removal river channel flow, sediment transport, and riverbed evolution processes are simulated.

[0137] Couple the fish habitat module to dynamically output the changes in HSI and WUA under different scenarios.

[0138] S4: Construction of multi-objective optimization decision model;

[0139] S41: Calculation of river connectivity index (RCI);

[0140] The graph theory method is used to quantify the longitudinal connectivity before and after dam removal. The formula is:

[0141]

[0142] Among them, L i is the length of the connected river section, and C i is the obstacle influence coefficient (set to 0 after dam removal);

[0143] S42: Multi-objective comprehensive evaluation;

[0144] Construct an objective function set: maximize the WUA increment, maximize the RCI improvement value, and minimize the dam removal cost;

[0145] Use a multi-objective optimization algorithm to screen the Pareto optimal solution set, and determine the final solution through the entropy weight-TOPSIS method.

[0146]

[0147] Among them: ΔWUA is the WUA increment of a certain solution; ΔRCI is the RCI improvement value of a certain solution; C is the total cost of a certain solution; W WUA is the WUA weight; W RCI is the RCI weight; W C is the cost weight.

[0148] S5: Dynamic restoration and effect verification;

[0149] S51: Implementation of restoration measures;

[0150] Remove the dam according to the optimized solution, and synchronously implement auxiliary measures: reshaping the micro-topography of the river channel (creating a deep pool-shoal sequence), arranging artificial fish nests, and restoring the vegetation of the riparian zone.

[0151] S52: Post-effect monitoring and model iteration;

[0152] Track the migration behavior of fish through acoustic tags to verify the improvement effects of HSI and WUA;

[0153] Use the monitoring data to correct the model parameters to form a "simulation-implementation-feedback" closed-loop optimization mechanism.

[0154] Example 3:

[0155] Three cascade power stations built on a mountainous river in a tributary of the Jinsha River have hindered the river connectivity and damaged the fish migration channels.

[0156] Protected fish species: Schizothorax wangchiachii

[0157] 1. Through field investigations, laboratory experiments, and corresponding literature surveys, obtain the hydraulic preferences of the target fish Schizothorax wangchiachii, and obtain the habitat suitability curve (HSC) of Schizothorax wangchiachii.

[0158] 2. Habitat modeling before dam removal;

[0159] Construct a hydrodynamic model for dam removal, output water depth and flow velocity factors, combine with the habitat suitability curve, calculate the habitat suitability index (HIS), and further obtain the effective habitat area (WUA) before dam removal; calculate the longitudinal river connectivity CRI before demolition

[0160] 3. Construct hydrodynamic models for different dam removal scenarios;

[0161] Not demolished as a whole (current state, none of the three dams are demolished)

[0162] Scenario 1: Demolish the Sujiawan Dam;

[0163] Scenario 2: Demolish the Gongdefang Dam;

[0164] Scenario 3: Demolish the Songxin Dam;

[0165] Scenario 4: Demolish the Sujiawan and Gongdefang Dams;

[0166] Scenario 5: Demolish the Sujiawan and Songxin Dams;

[0167] Scenario 6: Demolish the Gongdefang and Songxin Dams;

[0168] Scenario 7: Demolish the Sujiawan, Gongdefang, and Songxin Dams;

[0169] Calculate the effective habitat area WUA under different dam removal scenarios through the hydrodynamic model and calculate the river longitudinal connectivity (CRI) using the corresponding formula, as shown in the following table:

[0170]

[0171] Based on the effective habitat area and river longitudinal connectivity obtained from the model: In the case of demolishing only one dam, Scenario 2 has the largest effective habitat area and the highest connectivity; in the case of demolishing two dams, Scenario 5 has the largest effective habitat area and the highest river connectivity; when all three dams are demolished, the effective habitat area is the largest and the river connectivity is the largest.

[0172] 4. The hierarchical design of the supporting restoration measures for the dam removal scenarios is as follows in the table:

[0173]

[0174] The supporting table of restoration measures for each dam removal plan is as follows:

[0175]

[0176] Description of key restoration technologies:

[0177] Remodeling of river micro-topography:

[0178] Implementation location: The range 0.5 - 2 km downstream of the removed dam;

[0179] Technical parameters:

[0180] Pool - riffle sequence ratio = 1:3 (pool depth 1.5 - 2 m, riffle flow velocity 0.3 - 0.8 m / s);

[0181] Bottom sediment grading: D50 = 15 - 30 cm (matching the spawning requirements of Schizothorax wangchiachii);

[0182] Effect: Improve the diversity of local flow patterns, with a WUA increase rate of 8% - 12%;

[0183] Deployment of artificial fish nests:

[0184] Materials: Bamboo branch bundles (diameter 40 cm, length 2 m) + basalt rocks (porosity 30% - 40%);

[0185] Deployment density: Set 3 - 5 groups per 100 m of river;

[0186] Monitoring index: The attachment density of fish eggs is increased to 85% of that in natural river sections;

[0187] Ecological flow regulation;

[0188] Regulation threshold:

[0189] Breeding period (April - June): Q ≥ 60% of the multi - year average flow;

[0190] Overwintering period (December - February): Q ≥ 40% of the multi - year average flow;

[0191] Implementation method: Pulse - type water release through the reserved flood - discharging facilities;

[0192] The superposition analysis of restoration effects is as follows in the table;

[0193]

[0194] 5. Suggestions on implementation priority;

[0195] Short - term priority plan:

[0196] Recommended Solution 5 (demolish Sujiawan + Songxin Dam) + Level II restoration measures, balancing cost-effectiveness (WUA increased by 28%, CRI increased by 0.15) and avoiding the high inundation risk area of Gongdefang Dam.

[0197] Long-term optimal solution:

[0198] Solution 7 (complete demolition) requires supporting Level III management measures, focusing on solving:

[0199] Sediment release control (it is recommended to demolish in phases, with annual sediment removal ≤ 100,000 m 3 );

[0200] Development of community alternative livelihoods (such as ecological fishery cooperatives);

[0201] Risk avoidance measures;

[0202] Install a dam-break monitoring sensor network for Gongdefang Dam (Solution 2);

[0203] Set up a temporary sediment filter dam (height 3 m, water permeability ≥ 70%) at the demolished section of Songxin Dam.

[0204] The above embodiments are only the preferred technical solutions of the present invention and should not be regarded as limitations on the present invention. The protection scope of the present invention should be the technical solutions recorded in the claims, including equivalent replacement solutions of the technical features in the technical solutions recorded in the claims. That is, equivalent replacement improvements within this scope are also within the protection scope of the present invention.

Claims

1. A method for restoring river fish habitats based on cascade dam removal, characterized in that: It includes the following steps: S1: Basic data collection and processing; S2: Modeling and assessment of pre-dam removal habitat suitability; S3: Design of dam removal plan and simulation of hydrodynamic model; S4: Construction of multi-objective optimization decision-making model; S5: Implementation of dynamic restoration measures and verification of effects.

2. The method for restoring river fish habitats based on stepped dam removal according to claim 1, characterized in that: The specific steps of S1 are as follows: S11: Collection of hydrological and topographic data: Collect the cascade dam parameters and historical hydrological data of the target river, and use unmanned aerial vehicle (UAV) aerial survey or remote sensing technology to obtain the river channel topographic data and construct a digital elevation model; S12: Investigation of fish habitat data: Obtain the distribution of spawning grounds and foraging grounds of target fish and the requirements of key environmental factors through underwater sonar and catch surveys, and establish a species-environment relationship database.

3. The method for restoring river fish habitats based on the removal of cascade dams according to claim 1, characterized in that: The specific steps of S2 are as follows: S21: Construction of habitat suitability curve: Calculate the suitability curves of target fish for flow velocity, water depth, and substrate using the weighted available area method; S22: Calculation of habitat suitability index and effective habitat area: Based on the habitat suitability curve and two-dimensional hydrodynamic model to simulate the pre-dam removal hydrological conditions, calculate the spatial distribution of habitat suitability index and effective habitat area.

4. The method for restoring river fish habitats based on the removal of stepped dams according to claim 3, characterized in that: The formula for calculating the suitability curves of target fish for flow velocity, water depth, and substrate using the weighted available area method in S21 is: Among them, W i is the weight of environmental factors, and S i (X) is the suitability function of each factor.

5. The method for restoring river fish habitats based on the removal of stepped dams according to claim 3, characterized in that: The formula for calculating the spatial distribution of habitat suitability index and effective habitat area based on the habitat suitability curve and two-dimensional hydrodynamic model to simulate the pre-dam removal hydrological conditions in S22 is: Among them, HSI: Habitat Suitability Index, is a comprehensive index that synthesizes the suitability of multiple environmental factors and is used to evaluate the quality of fish habitats; WUA: Effective Habitat Area, refers to the habitat area that fish can utilize under specific environmental conditions, calculated by the weighted available area method, reflecting the actual available space of fish in different habitats, and A i is the grid cell area.

6. The method for restoring the river fish habitat based on the removal of cascade dams according to claim 1, characterized in that: The specific steps of S3 are as follows: S31: Generation of dam removal plan combinations: Design full removal, partial removal, and staged removal modes, set the removal sequence, and design the ecological operation rules after dam removal in combination with the ecological flow requirements; S32: Construction of hydrodynamic-habitat coupling model: Based on the hydrodynamic model to simulate the river channel water flow, sediment transport, and riverbed evolution process after dam removal, couple the fish habitat module, and dynamically output the changes in habitat suitability index and effective habitat area under different plans.

7. The method for restoring river fish habitats based on cascade dam removal according to claim 1, characterized in that: The specific steps of S4 are as follows: S41: Calculation of river connectivity index RCI; S42: Multi-objective comprehensive evaluation.

8. The method for restoring river fish habitats based on the removal of stepped dams according to claim 7, characterized in that: The specific content of S41 is: Quantify the longitudinal connectivity before and after dam removal using graph theory method, and the formula is: Among them, L i is the length of the connected river section; C i is the obstacle influence coefficient, which is set to 0 after the dam is removed; L total is the total length in the ideal state or the research scope.

9. The method for restoring river fish habitats based on the removal of cascade dams according to claim 7, characterized in that: The specific content of S42 is: Construct an objective function set: maximize the increase in WUA, maximize the improvement value of RCI, and minimize the dam removal cost; Use a multi-objective optimization algorithm to screen the Pareto optimal solution set, and determine the final plan through the entropy weight-TOPSIS method; Where: ΔWUA is the WUA increment of a certain solution; ΔRCI is the RCI improvement value of a certain solution; C is the total cost of a certain solution; W WUA is the WUA weight; W RCI is the RCI weight; W C is the cost weight. Where: ΔWUA is the WUA increment of a certain solution; ΔRCI is the RCI improvement value of a certain solution; C is the total cost of a certain solution; W WUA is the WUA weight; ΔWUA MAX is the maximum WUA increment among all solutions; W RCI is the RCI weight; ΔRCI MAX is the maximum RCI improvement value among all solutions; W C is the cost weight; C MIN is the lowest cost among all solutions.

10. The method for restoring river fish habitats based on the removal of cascade dams according to claim 1, characterized in that: The specific steps of S5 are as follows: S51: Implementation of restoration measures: Remove the dam according to the optimized plan, and synchronously implement auxiliary restoration measures, including reshaping of river channel micro-topography, installation of artificial fish nests, and restoration of riparian vegetation; S52: Post-effect monitoring and model iteration: Track the fish migration behavior through acoustic tags, verify the improvement effect of habitat suitability index and effective habitat area after dam removal, and use the monitoring data to correct the model parameters to form a closed-loop optimization mechanism of "simulation-implementation-feedback".

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