Yangtze river source area fish spawning habitat construction method adapting to dynamic evolution of braided river channel

Abstract

The invention relates to a Yangtze river source area fish spawning habitat construction method adapting to dynamic evolution of a braided river channel. The method comprises the following steps: site selection and hydraulic diagnosis of a construction site; carrying out branch channel stabilizing treatment and internal habitat building; constructing an anti-impact-adhesion integrated bed sand layer; and dynamic monitoring and adaptive maintenance. According to the method, the long-acting spawning habitat with branch channel stability and ecological adaptability can be constructed, the problem of imbalance and instability of the indigenous fish breeding habitat in the source area is effectively solved, and the ecological adaptability and engineering practicability are remarkable.

Description

Technical Field

[0001] This application relates to the field of river ecological restoration and water conservancy engineering technology, specifically to a method for actively constructing and adaptively maintaining a stable fish spawning habitat by means of the synergistic effect of hydraulic regulation and bed sediment configuration, targeting the dynamic habitat characteristics of typical braided river channels in high-altitude and cold regions such as the Yangtze River source area. Background Technology

[0002] The Yangtze River source region is characterized by widespread, typical braided channels, featuring wide, shallow channels, dispersed currents, and frequent migration of mid-channels and sandbars. The riverbed is primarily composed of gravel and sand. The highly dynamic evolution of these channels makes naturally formed fish spawning grounds extremely unstable: intense scouring during floods can bury or wash away suitable gravel substrates, while sudden drops in water levels during the dry season expose spawning grounds, leading to egg mortality. The main fish groups in this region are schizothorax fish (such as the small-headed schizothorax and the naked-bellied leaf-whiskered fish) and plateau loaches. Their spawning and juvenile rearing activities are highly dependent on microhabitats such as meandering channels and slow-flowing areas with specific water depths, flow velocities, and substrate conditions.

[0003] Currently, conventional fish habitat restoration techniques are mostly applicable to river sections with static or stable hydrological conditions, or rely on rigid, solidified engineering structures (such as continuous rigid groynes and guide walls). These methods attempt to counteract or fix the natural flow path and are difficult to adapt to the dynamic characteristics of braided river channels, such as frequent main channel oscillation and intense scouring and deposition. They not only easily disturb the natural river morphology, exacerbate local scouring or deposition, and may even cause shoreline retreat, but the engineering structures themselves often fail due to rapid changes in the river channel, thus failing to achieve long-term, stable ecological functions.

[0004] Therefore, existing technologies lack a method for constructing spawning grounds that can adapt to rather than resist the dynamic natural evolution of braided river channels. The core challenge lies in identifying and stabilizing a relatively stable secondary flow path within a constantly changing river channel, and then actively creating and maintaining key habitat parameters (including suitable water depth, flow velocity, substrate composition, and stable bank boundaries) within the river channel using low-intervention, adaptive engineering methods. This would form a long-term spawning habitat that coexists symbiotically with the dynamic river channel. This has become a critical technical bottleneck that urgently needs to be overcome in the ecological protection and restoration of braided river channels in plateau regions. Summary of the Invention

[0005] The purpose of this application is to overcome the shortcomings of the existing technology and provide a method for constructing fish spawning habitats in the Yangtze River source area that adapts to the dynamic evolution of braided channels. Instead of attempting to solidify or forcibly change the main channel, it first ensures the stability of the inflow and outflow of a secondary channel, and then creates the target habitat in a refined manner through flexible structures within it. The erosion resistance stability of key structures is ensured through theoretical calculations, and finally, the synergistic coexistence of habitat patches and channel dynamics is achieved.

[0006] To achieve the above objectives, this application provides the following technical solution:

[0007] This application provides a method for constructing a hydraulic-bed-sand synergistic fish spawning habitat adapted to the dynamic evolution of braided channels, including the following steps:

[0008] S1. Structural location selection and hydraulic diagnosis:

[0009] Based on hydrological data, remote sensing imagery, and field surveys, the evolution history and trends of the target braided river segment were analyzed. Following the principle of "avoiding the main channel and selecting secondary channels, seeking stability and gentleness," a non-main channel with smooth flow during the mid-water season and relatively stable banks was prioritized as a candidate area. Furthermore, the candidate area should ideally possess geomorphic features conducive to habitat stability, such as a river width of 10-20 meters and a longitudinal aspect ratio lower than 200 dk. Hydrodynamic model simulations or field measurements were used to diagnose the velocity and depth distribution of the candidate area under typical flow rates during the fish spawning season, ultimately determining the specific extent and layout axis of the tectonic zone.

[0010] S2, Channel stabilization treatment and internal habitat creation:

[0011] This step aims to first ensure the stability of the water flow channels in the tectonic zone, and then meticulously create the target habitat within it, comprising three sub-steps:

[0012] (1) Stabilization project for the inlet and outlet of the distributary: For the selected distributary, the inlet section is appropriately widened, and the banks are reinforced by means of gabions, ecological bags or riprap to ensure that it can stably and smoothly receive the diversion from the main distributary. At the same time, the outlet section of the distributary is dredged to prevent siltation from causing water flow obstruction and to ensure smooth water flow and stable flow path of the distributary as a whole.

[0013] (2) Layout and bank slope protection of permeable biomimetic groynes: Within the stabilized channel, a group of low, permeable groynes constructed of natural boulders is laid along the near-bank side. The groynes' axes form a certain angle (preferably 60°-120°) with the main flow direction. Their function is to allow most of the water flow to pass smoothly while creating a significant hydraulic shadow area behind the groynes (on the backflow side), thus precisely shaping a still water zone (velocity <0.05 m / s) and a slow-flow zone (velocity <0.3 m / s) with the required flow velocity, maintaining the target water depth between 0.1 and 0.4 meters. Flexible protection must be provided to the bank slope supporting the slow-flow zone created by the groynes to prevent scouring and bank retreat. Engineering measures include, but are not limited to, ecological gabions, vegetation mats, or riprap protection.

[0014] (3) Creation of spawning ponds: In the still and slow-flowing areas on the back side of the aforementioned groynes, a micro-topography of alternating shallow pits and shoals is created through local excavation or by using natural hydraulic adjustment. The shallow pits are 0.2-0.4 meters deeper than the surrounding riverbed, and the shoals are slightly higher than the surrounding riverbed, thus forming a water depth gradient of 0.1-0.3 meters in a local area, providing diverse habitat options for fish.

[0015] S3, Construction of an integrated erosion-resistant and adhered sand bed layer:

[0016] In the prepared spawning pond area, a composite sand bed layer is constructed from bottom to top, which combines the stability against flood erosion with the adaptability for fish spawning attachment. Each layer complements the function and works synergistically to ensure the long-term stability of the habitat. The specific structure is as follows:

[0017] Filter layer: A layered laying process is adopted, with clean sand and gravel with a particle size of 2-16mm (thickness 0.1-0.15m) and natural gravel with a particle size of 16-64mm (thickness 0.1-0.15m) laid sequentially from bottom to top, with a total thickness controlled at 0.2-0.3m and a porosity maintained at 30%-40%. Its core function is to prevent the loss of fine particles from the bottom soil with the seepage water flow through the continuously graded particle combination, thus avoiding the overall collapse of the bed sand layer; at the same time, it ensures the vertical permeability of the bed sand layer, realizing the downward infiltration and upward circulation of water, laying the foundation for maintaining an aerobic environment for the subsequent oviposition layer.

[0018] Spawning Attachment Layer: Lay on top of the filter layer, this is the core functional layer of the spawning ground, with a porosity controlled at 35%-45%. The main body consists of clean, natural river pebbles, requiring a silt content of less than 5%, a particle size of 16-64mm, and a thickness of no less than 0.15m. The gap width between pebbles within this particle size range is 5-20mm, precisely matching the egg diameter (2-4mm) of native fish species such as the schizothorax in the Yangtze River source area. This provides stable attachment points for the eggs, and the interstitial water flow continuously replenishes oxygen, meeting the needs of embryonic development. To accommodate the burial habits of some fish species, clean fine sand with a particle size of 2-4mm is laid in the still water and slow-flowing areas (flow velocity <0.3m / s) of the spawning ponds. This fine sand area is enclosed by 16-64mm gravel to prevent diffusion, with a thickness of no less than 0.15m, ensuring burial depth and egg safety.

[0019] Surface stabilizing layer: Lay on top of the spawning attachment layer, using a semi-buried sparse distribution process. Natural pebbles or boulders with a diameter of 150-300mm are selected, with a density of 1-1.5 pebbles / m², and a spacing of 0.8-1.2m between pebbles. The pebbles are embedded 5-10cm into the spawning attachment layer to enhance the interlocking and anchoring effect, with a pebble spacing ratio ≥50%. Its functions are: ① To disperse water flow energy and increase substrate roughness through the erosion resistance stability of the large-diameter pebbles (verified using the modified Meyer-Peter formula, meeting erosion resistance requirements), thus inhibiting the overall activation of the underlying filter layer and spawning attachment layer during floods; ② To create a slow-flowing micro-habitat between pebbles, providing shelter for juvenile fish from rapids and predators; ③ To avoid obscuring the spawning attachment layer and ensure unobstructed spawning channels for fish.

[0020] The design of the particle size of the bed sand layer, especially the surface stable layer, must meet the stability requirements against flood erosion. Its stability should be based on the initiation characteristics of coarse-grained sediment in the braided channels of the Yangtze River source region, and verified through sediment kinematics theory. Preferably, a modified Maye-Peter initiation criterion adapted to the wide and shallow channels and the non-uniform coarse-grained sediment characteristics of the source region should be used for verification, ensuring that under certain flood conditions (e.g., a 20-year return period), the actual shear stress (τ0) of the water flow on the riverbed does not exceed the critical initiation shear stress (τ) of the boulders. c ),Right now:

[0021] τ0≤τ c =0.047·(ρ s -ρ)·g·D

[0022] The definitions of each parameter and the appropriate values ​​for the Yangtze River source region are as follows:

[0023] τ0 is the actual shear stress of the water flow (Pa), which is determined by the average water depth of the river channel under the design flood condition (h). d ), natural gradient (J) and water body bulk density (γ) m =ρ·g) is calculated to obtain τ0=γ m ·h d ·J; 0.047 is a correction factor for coarse-grained channels in mountainous areas, verified by measured data from braided channels in the Yangtze River source region; ρ s ρ and ρ' are the densities of the boulders (natural granite / gneiss) and the low-temperature water in the Yangtze River source area, respectively, with values ​​of 2650 kg / m³. 3 998kg / m 3 g is the acceleration due to gravity, taken as 9.81 m / s². 2 D represents the minimum design particle size (m) of the boulders in the stable surface layer of the bed sand. Furthermore, considering spring meltwater floods (including ice debris and fluctuations in water flow resistance), a safety factor K of 1.1~1.2 needs to be introduced for correction, leading to the following formula for calculating the minimum design particle size of the boulders:

[0024] D≥(K·γ m ·h d ·J) / (0.047·(ρ s -ρ)·g)

[0025] This calculation effectively matches the characteristics of the Yangtze River source area, such as low temperature, wide and shallow water, rapid current, and high bed surface roughness. Theoretically, it ensures the long-term erosion resistance stability of the bed sand structure, especially the surface stable layer, under design floods and extreme hydrological conditions, while also taking into account the spawning and attachment needs of native fish species in the source area.

[0026] S4. Dynamic monitoring and adaptive maintenance:

[0027] To ensure the long-term sustainability of tectonic habitats, adaptive maintenance based on monitoring is implemented. Monitoring of the tectonic zone is conducted before and after the spawning season and flood season, focusing on: water depth and velocity distribution, bed sediment composition, micro-topography and bank stability, and fish utilization. Based on the monitoring results, precise and light maintenance is carried out, such as: replacing and reshaping displaced or damaged groynes; performing maintenance dredging at the inlets and outlets of silted-up channels; repairing damaged bank protection; quantitatively replenishing eroded gravel from the spawning layer; and locally dredging severely silted-up ponds to restore their designed function.

[0028] Beneficial effects of the present invention

[0029] Through the four-step collaborative design method described above, this invention achieves the following beneficial effects: 1) By prioritizing the stabilization of the inlet and outlet of the channel, a stable basic flow path platform is provided for habitat creation, reducing the risk of overall project failure due to river channel swaying; 2) By utilizing a group of permeable groynes for precise and minimally invasive hydraulic control within the stable flow path, the target habitat flow field is efficiently formed, and the stability of the habitat boundary is ensured through the protection of the corresponding bank slopes; 3) By introducing hydraulic theory to verify the stability of the bed sediment, the bed sediment design is elevated from empirical judgment to theoretical guarantee, significantly improving the reliability of the constructed habitat against flood erosion. Ultimately, this invention, under the premise of adapting to the natural evolution law of braided channels, can proactively construct a fish spawning ground with stable habitat parameters, safe boundaries, and sustainable ecological functions, realizing the scientific creation and long-term maintenance of stable habitats in dynamic river channels. Attached Figure Description

[0030] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments of this application will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 This is a schematic diagram illustrating the evolution analysis of braided river channels and the site selection of tectonic zones.

[0032] Figure 2 Schematic diagram of the layout and structural relationship of the spawning grounds

[0033] Figure 3 Schematic diagram of a permeable groyne group

[0034] Figure 4 A schematic diagram of the hierarchical structure of the integrated erosion-adhesion bed sand layer.

[0035] Figure 5 A flowchart for the construction and adaptive maintenance of spawning ground structures. Detailed Implementation

[0036] The technical solutions of the embodiments of this application will now be described with reference to the accompanying drawings. It should be noted that similar reference numerals and letters in the following drawings indicate similar items; therefore, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings.

[0037] The terms “comprising,” “including,” or any other variations thereof are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase “comprising one…” does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0038] The terms “first,” “second,” etc., are used only to distinguish one entity or operation from another, and should not be construed as indicating or implying relative importance, nor as requiring or implying any such actual relationship or order between these entities or operations.

[0039] Example: Constructing a spawning habitat for *Gymnocypris scutellarioides* in a typical braided river section in the source region of the Yangtze River.

[0040] This embodiment aims to specifically illustrate the implementation process and application effects of the method of the present invention.

[0041] S1. Structural location selection and hydraulic diagnosis:

[0042] By analyzing historical satellite imagery and hydrological data, a stable distributary within the target braided river section was selected as the structural zone. This distributary is a non-main channel with a smooth flow during the mid-water period (flow frequency approximately 50%), and one bank is covered by a meadow with good erosion resistance. Field investigation confirmed that the distributary is approximately 15 meters wide with a longitudinal gradient of approximately 150 dk, meeting the preferred criteria of "low gradient and narrow width." On-site measurements using an Acoustic Doppler Current Profiler (ADCP) showed that under typical flow conditions during the late spring spawning season for the target fish (Gymnocypris scutellarioides), the average flow velocity in this area was approximately 0.7 m / s, and the average water depth was approximately 0.3 m. However, the riverbed sediment was predominantly bedload sand, lacking a stable gravel spawning substrate.

[0043] S2. Construction of channel stabilization treatment and internal habitat creation:

[0044] (1) Construction at the entrance and exit: First, the entrance section of the selected channel, about 20 meters in length, is widened appropriately, and gabion mesh is used to reinforce the right bank (the side facing the current). At the same time, the exit section of the channel, about 15 meters in length, is dredged to remove silt and ensure smooth and stable flow in and out.

[0045] (2) Construction of permeable groynes and bank slope protection: Near the left bank of the completed channel section, three permeable biomimetic groynes were constructed by excavating natural boulders (marked as 7 in the figure) by dumping natural boulders. The groynes were about 8-10m long, with the top elevation about 0.4m above the riverbed. The groynes were permeable, and their axis was at an angle of about 75° to the direction of water flow. After construction, a distinct still water zone (10) and a slow-flowing zone (11) were formed on the back side of the groynes. Measurements showed that the flow velocity in the slow-flowing zone dropped to 0.2-0.25m / s, the flow velocity in the still water zone was below 0.05m / s, and the water depth was between 0.1-0.35m. Subsequently, ecological gabions were laid on the left bank slope on which the still water zone (10) and the slow-flowing zone (11) were located for protection (marked as 4 in the figure).

[0046] (3) Shaping of the pit group: In the formed still water area (10) and slow flow area (11), a long-arm excavator was used to shape the micro-topography of the spawning pit group (6). A total of 5 irregular shallow pits (71) were excavated, which were about 0.3m deeper than the original riverbed and 2-3m in diameter; the excavated sand and gravel were piled up between the pits to form shoals (72), providing a water depth variation of 0.1-0.4m.

[0047] S3. Construction of an integrated erosion-resistant and buoyancy-adhesion sand bed: In the prepared shallow pit (61) and some shallow beach (62) areas, a composite functional sand bed layer with both erosion resistance and ecological adaptability is laid in layers from bottom to top. The construction sequence and technical requirements are as follows:

[0048] Filter layer (8): First, a filter layer with a total thickness of about 0.25m is constructed using a layered laying process. From bottom to top, it consists of a clean sand and gravel layer with a particle size of 2-16mm (thickness 0.12m) and a natural gravel layer with a particle size of 16-64mm (thickness 0.13m), controlling the overall porosity of the filter layer to 30%-40%. This structure can prevent the loss of fine particles of the bottom soil with the seepage water flow, avoid the collapse of the bed sand layer, and at the same time ensure vertical permeability and maintain the aerobic environment of the subsequent functional layers.

[0049] Spawning attachment layer (9): On the filter layer, a spawning attachment layer with a thickness of not less than 0.15m is laid, and the porosity is controlled to be 35%-45%. The main body of this layer is made of natural river pebbles with a clean surface, a silt content of less than 5%, and a particle size of 20-50mm (belonging to the preferred range of 16-64mm particle size). The gap size is adapted to the height of the egg diameter of the source area of ​​the schizothorax fish, providing an ideal substrate for the attachment of fish eggs. In the slow-flowing edge area (flow velocity <0.3m / s) of the shallow pit (71) and the shallow beach (72), a clean fine sand area with a particle size of 2-4mm is laid. The fine sand area is surrounded by 16-64mm gravel to prevent diffusion. The thickness is not less than 0.15m, which meets the egg burial and reproduction requirements of the small-headed naked schizothorax.

[0050] Surface stabilization layer (10): Finally, at a density of about 1 piece / square meter, natural large stones with a particle size of 150-300mm are sparsely distributed using a semi-buried process as the surface stabilization layer; the stones are embedded 5-10cm into the spawning attachment layer to enhance the interlocking and anchoring effect, and the gap rate of the stones is controlled to ≥50% to avoid obscuring the spawning matrix. The determination of the particle size range of the boulders was based on the hydrodynamic simulation results of a 20-year flood during the spawning season in this river section (design flood depth 1.8m, channel gradient 0.0019). The modified Meyer-Peter start-up criterion, adapted to the coarse-grained characteristics of the braided channel in the Yangtze River source area, was used for verification, and a safety factor of 1.15 was introduced to cover the extreme conditions of spring ice melt floods. After verification, 150mm was found to be the minimum particle size to meet the erosion resistance requirements. Considering the convenience of engineering construction and the need for protection of juvenile fish, the particle size range was finally determined to be 150-300mm, ensuring that the boulders do not start under the design flood and extreme hydrological conditions, and effectively anchoring the underlying sand layer structure.

[0051] S4. Dynamic monitoring and adaptive maintenance:

[0052] After the project was implemented, monitoring was conducted for a full hydrological year (including the flood season):

[0053] Post-flood assessment: The following year, after the flood season, comparison of UAV orthophotos and topographic scans showed that the reinforced channel inlet and outlet remained in good condition, the main structure of the permeable groynes (3) was stable, and a small number of boulders at the base were washed downstream, forming new secondary habitats. The bank slope protection (6) was intact, the overall topography of the spawning pond group (7) was maintained, with slight local siltation.

[0054] Ecological function verification: During the spawning season (May-June), underwater observation confirmed that the small-headed naked carp had successfully spawned on the spawning attachment layer (9) of the pond group.

[0055] Adaptive maintenance: Based on monitoring results, minimal intervention was implemented: one shallow pit with severe siltation was partially dredged and approximately 3 m³ of clean small and medium-sized pebbles were added.

[0056] The above description is merely an embodiment of this application and is not intended to limit the scope of protection of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A method for constructing fish spawning habitats in the source region of the Yangtze River to adapt to the dynamic evolution of braided channels, characterized in that, The method comprises the following steps: S1, constructing a location site and hydraulic diagnosis: based on the river evolution history and water power simulation of the target braided river section, a branch other than the main channel is selected as the construction area; the branch is smooth in the middle water period, the river bank is relatively stable, and has a relatively gentle longitudinal slope; S2, branch stabilization treatment and internal habitat creation: the inlet section of the branch is widened and the bank slope is reinforced, and the outlet section is dredged to form stable inflow and outflow conditions; a discontinuous, low, and water-permeable bionic dike group made of natural block stones is arranged on the inner near-shore side of the stabilized river, which is used to guide and disperse water flow, and form a flow field pattern mainly composed of static water areas and slow flow areas in the construction area; the bank slope relying on the slow flow area is flexibly protected; at the same time, a spawning pit pond group microtopography is shaped in the hydraulic shadow area on the backflow side of the dike group; S3, construction of an integrated bed sand layer with anti-erosion and attachment: in the spawning pit pond group area, a special gradation artificial bed sand layer is laid from bottom to top, which includes a filter layer, a spawning attachment layer, and a surface stabilization layer; S4, dynamic monitoring and adaptive maintenance: during the spawning season and before and after the flood period, the water depth, flow velocity, bottom composition, topographic stability, and bank slope state of the construction area are monitored, and the flow guide structure, pit pond topography, bed sand layer, and bank protection are supplemented and maintained according to the monitoring results.

2. The fish spawning habitat construction method for adapting to the dynamic evolution of braided channel in the Yangtze River source region according to claim 1, characterized in that: In step S1, a stable branch with a river width of 10-20 meters and a longitudinal slope of less than 200dk is selected as the construction area.

3. The fish spawning habitat construction method for adapting to the dynamic evolution of braided channel in the Yangtze River source region according to claim 1, characterized in that: In step S2, the static water area and slow flow area shaped by the bionic dike group have a target water depth range of 0.1-0.4 meters, with a flow velocity of not more than 0.3 m / s in the slow flow area and not more than 0.05 m / s in the static water area.

4. The fish spawning habitat construction method for adapting to the dynamic evolution of braided channel in the Yangtze River source region according to claim 1, characterized in that: In step S2, the depth of the shallow pit in the spawning pit pond group is 0.2-0.4 meters deeper than the surrounding riverbed, and the elevation of the shallow beach is slightly higher than the surrounding riverbed, thereby forming a water depth change gradient of 0.1-0.3 meters locally.

5. The fish spawning habitat construction method for adapting to the dynamic evolution of braided channel in the Yangtze River source region according to claim 1, characterized in that: In step S2, the bank slope relying on the static water area and slow flow area is flexibly protected by using ecological gabions, riprap, or vegetation blankets.

6. The fish spawning habitat construction method for adapting to the dynamic evolution of braided channel in the Yangtze River source region according to claim 1, characterized in that: In step S3, the anti-erosion and attachment integrated bed sand layer is constructed from bottom to top, specifically including: The filter layer, from bottom to top, includes a clean sand and gravel layer with a particle size of 2-16 mm and a natural gravel layer with a particle size of 16-64 mm, wherein the clean sand and gravel layer has a thickness of 0.1-0.15 m, the natural gravel layer has a thickness of 0.1-0.15 m, the total thickness of the filter layer is 0.2-0.3 m, and the porosity is controlled at 30-40%; The egg-laying attachment layer is laid on the inverse filtration layer, the porosity is controlled to be 35% to 45%, the main body is composed of clean natural river pebbles, and the laying thickness is not less than 0.15 m; in the slow flow edge area of the egg-laying pit pond, the flow velocity is less than 0.3 m / s, the clean fine sand area with a particle size of 2 mm to 4 mm is arranged, the fine sand area is surrounded by gravel with a particle size of 16 mm to 64 mm, the fine sand laying thickness is not less than 0.15 m, and the fish with part of the egg-burying demand is used; The surface stable layer is composed of natural large pebbles or boulders with a particle size of 150 mm to 300 mm, is covered on the egg-laying attachment layer in a semi-buried sparse scattering mode, the arrangement density is 1 piece / ㎡ to 1.5 pieces / ㎡, the boulder spacing is 0.8 m to 1.2 m, the depth of the boulder embedded in the egg-laying attachment layer is 5 cm to 10 cm, and the boulder gap rate is greater than or equal to 50%.

7. The fish spawning habitat construction method for adapting to the dynamic evolution of braided channel in the Yangtze River source region according to claim 6, characterized in that: The surface of the natural river pebbles of the egg-laying attachment layer is clean, and the particle size of the river pebbles is 16 mm to 64 mm.

8. The fish spawning habitat construction method for adapting to the dynamic evolution of braided channel in the Yangtze River source region according to claim 6, characterized in that: In the step S3, the particle size of the large pebbles or boulders of the surface stable layer needs to be determined based on the bed surface shear stress under the design flood condition of the target river section in the 20-year egg-laying period, and is determined by using the modified Meyer-Peter start formula; if the design condition includes spring ice-melting flood, a safety factor is introduced for correction, so that the large pebbles or boulders can meet the requirements of anti-scouring stability under the design flood and extreme hydrological conditions.

9. The fish spawning habitat construction method for adapting to the dynamic evolution of braided channel in the Yangtze River source region according to claim 1, characterized in that: The adaptive maintenance in the step S4 specifically includes: supplementing and reorganizing the bionic dike structure which is displaced or damaged according to the terrain scanning result, and carrying out maintenance dredging at the entrance and exit of the branch; repairing the damaged protection structure according to the bank slope monitoring result; quantitatively supplementing the lost egg-laying attachment layer gravel according to the bottom material sampling result; and locally dredging the egg-laying pit pond which has serious siltation to restore the design water depth and shape.

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