Oyster reef ecological restoration method based on tidal flat after sea reclamation

Abstract

The present application relates to the technical field of animal husbandry or fishing, and specifically to an oyster reef ecological restoration method based on tidal flats after sea reclamation, which is executed by a controller and includes: performing ecological restoration area division on the tidal field enclosure of the target area; obtaining the layout position of the oyster reef in the ecological restoration area; establishing a non-uniform sediment dynamic model of the target area; establishing a geomorphic model of the target area; integrating the non-uniform sediment dynamic model with the geomorphic model to establish a non-uniform sediment dynamic geomorphic model; determining a scenario simulation based on at least the action of tidal currents, waves, and oyster reefs, inputting the scenario simulation into the non-uniform sediment dynamic geomorphic model, obtaining the restoration result; and evaluating the restoration effect. The present application solves the problem that the prior art cannot effectively utilize oyster reefs to achieve ecological restoration of tidal flats after sea reclamation.

Description

Technical Field

[0001] The present application relates to the technical field of animal husbandry or fishing, and in particular to an ecological restoration method for oyster reefs based on tidal flats after sea reclamation. Background Art

[0002] The coastal zone is a transition zone between land and sea, and is also a typical interlaced zone for the coordinated development of land and sea ecosystems. Reclamation of coastal areas to obtain land resources is a relatively frequent coastal disturbance activity by humans. However, the direct occupation of tidal flats by reclamation areas leads to the disappearance and migration of organisms. The rapid advancement of the coastline to the sea caused by reclamation will disturb the natural evolution of the tidal flat system, including significant changes in the dynamic process of water flow and sediment transport, underwater topography and bottom environment, which will bring about a series of negative effects such as marine habitats and biological connectivity, leading to the degradation and even loss of ecosystems.

[0003] Oyster reefs are "ecosystem engineers" in the ocean and an important component of maintaining nearshore biodiversity and ecosystem stability. The patent that has been published is a Chinese patent with the name of "An ecological construction and restoration method and system for oyster reefs in ecological seawalls" and application number 202410161543.5. Although this patent provides a method for ecological restoration using oyster reefs, it is used for ecological restoration of seawalls. Due to different dynamic conditions, this method cannot effectively achieve ecological restoration of tidal flats after sea reclamation. Summary of the invention

[0004] The purpose of the present application is to provide an oyster reef ecological restoration method based on tidal flats after sea reclamation, which solves the problem in the prior art that oyster reefs cannot be effectively utilized to achieve ecological restoration of tidal flats after sea reclamation.

[0005] The technical solution of this application:

[0006] The present application provides an oyster reef ecological restoration method based on tidal flats after sea reclamation, which is executed by a controller and includes:

[0007] Demarcate the target area tidal field and implement ecological restoration area division;

[0008] Obtain the location of oyster reefs in the ecological restoration area;

[0009] Establish a non-uniform sediment dynamic model for the target area;

[0010] Establish a geomorphic model of the target area;

[0011] The non-uniform sediment dynamic model is integrated with the geomorphic model to establish a non-uniform sediment dynamic geomorphic model;

[0012] Determine scenario simulation based on at least tidal action, wave action, and oyster reef action, input the scenario simulation into the heterogeneous sediment dynamic geomorphology model, and obtain restoration results;

[0013] Perform an evaluation of the repair effectiveness.

[0014] In some embodiments, the ecological restoration area division for enclosing the tidal field of the target area is specifically: division according to the direction and movement pattern of waves and water currents in the target area.

[0015] In some embodiments, the method of obtaining the layout position of oyster reefs in the ecological restoration area is specifically as follows: according to the water flow characteristics of the target area, three oyster reef belts are determined to be arranged in an interval manner.

[0016] In some embodiments, the process of constructing the non-uniform sediment dynamics model is: constructing a hydrodynamic model and a sediment model, and fusing the non-uniform sand parameters with the hydrodynamic model and the sediment model to form the non-uniform sediment dynamics model.

[0017] In some embodiments, the hydrodynamic model includes: simulating tidal flat waves, wherein the wave frequency is 15%, the effective wave height is 0.5 m, and the spectrum peak period is 5.7 s.

[0018] In some embodiments, the scenario simulations are at least four types: tidal current only simulation, tidal current-wave simulation, tidal current-oyster reef simulation, tidal current-wave-oyster reef simulation.

[0019] In some embodiments, the simulation time of the non-uniform sediment dynamics model is 7 days.

[0020] In some embodiments, the evaluation of the restoration effect is specifically as follows: using the restoration result parameters obtained in the scenario where only tidal currents act as baseline parameters, comparing the restoration result parameters in other scenarios with the baseline parameters, and evaluating the restoration effect, wherein the flow velocity, wave height, wave height attenuation coefficient, maximum near-bottom shear stress, peak sediment content, peak value of reduced sediment content, net sediment transport direction, and siltation intensity before and after the oyster reef are set for the above four scenarios to determine the restoration effect.

[0021] The technical solution of the present application has at least the following advantages and beneficial effects:

[0022] The present application provides an oyster reef ecological restoration method based on tidal flats after sea reclamation. By establishing a non-uniform sediment dynamic geomorphological model, specifically by constructing a hydrodynamic model, a sediment model and a geomorphological model, real-time data exchange can be performed between different models to achieve coupling between different physical processes, so that the ecological restoration simulation of the tidal flats after sea reclamation is closer to the actual situation, so that the implementation can achieve better restoration effects, and solves the problem that the existing technology cannot effectively utilize oyster reefs to achieve ecological restoration of tidal flats after sea reclamation. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 A schematic diagram of the process of oyster reef ecological restoration method provided for this application;

[0024] Figure 2 This is a schematic diagram of the target area division in this application;

[0025] Figure 3 A schematic diagram of the locations of oyster reefs in this application;

[0026] Figure 4 This is an example table of the simulated scenarios in this application;

[0027] Figure 5 This is a schematic diagram of the difference in water flow velocity when there is an oyster reef or not during rapid water flow in Example 2 of the present application;

[0028] Figure 6 This is a schematic diagram of the difference in water flow velocity when there is an oyster reef or not in the emergency falling moment of Example 2 of the present application;

[0029] Figure 7 This is a schematic diagram of flow velocity distribution after oyster reef ecological restoration under the action of pure tidal current during rapid rise in Example 2 of the present application;

[0030] Figure 8 This is a schematic diagram of flow velocity distribution after oyster reef ecological restoration under the action of pure tidal current during rapid fall in Example 2 of the present application;

[0031] Fig. 9 This is a schematic diagram of the difference in flow velocity before and after oyster reef ecological restoration under the action of pure tidal current during rapid rise in Example 2 of the present application;

[0032] Fig.10 This is a schematic diagram of the difference in flow velocity before and after oyster reef ecological restoration under the action of pure tidal current during rapid fall in Example 2 of the present application;

[0033] Fig.11 This is a schematic diagram of the difference in tidal flow direction after oyster reef ecological restoration under the action of pure tidal current during rapid rise in Example 2 of the present application;

[0034] Fig.12 This is a schematic diagram of the difference in tidal flow direction after oyster reef ecological restoration under the action of pure tidal current during a rapid fall in Example 2 of the present application;

[0035] Fig.13 This is the distribution diagram of the sand content at the time of rest without oyster reefs in the target area under the action of pure tidal current in Example 2 of the present application;

[0036] Fig.14 This is a distribution diagram of the sand content when there is an oyster reef in the target area under the action of pure tidal current in Example 2 of the present application;

[0037] Fig.15 This is a graph showing the change in sediment content at the time of swell and rest before and after ecological restoration of oyster reefs under the action of pure tidal currents in Example 2 of the present application;

[0038] Fig.16 This is a schematic diagram of the change in the direction of residual sand transport of the oyster reef sand capture effect under the action of pure tidal current in Example 2 of the present application;

[0039] Fig.17 This is a schematic diagram of the variation of the residual sand transport intensity of the oyster reef sand capture effect under the action of pure tidal current in Example 2 of the present application;

[0040] Fig.18 This is a schematic diagram of the effect of waves on the flow blocking effect of oyster reefs during rapid rise in Example 2 of the present application;

[0041] Fig.19 This is a schematic diagram of the effect of waves on the flow blocking effect of oyster reefs during rapid fall in Example 2 of the present application;

[0042] Fig. 20 This is a schematic diagram of the flow-blocking effect of oyster reefs under the combined action of waves and tidal currents and the action of pure tidal currents during rapid rise in Example 2 of the present application;

[0043] Fig.21 This is a schematic diagram of the flow-blocking effect of the oyster reef under the combined action of waves and tidal currents and the pure tidal currents during a rapid fall in Example 2 of the present application;

[0044] Fig. 22 This is a schematic diagram of wave height variation under the combined action of waves and tidal currents in Example 2 of the present application;

[0045] Fig.23 This is a schematic diagram of the wave height attenuation coefficient under the combined action of waves and tidal currents in Example 2 of the present application;

[0046] Fig.24 This is a schematic diagram of the theoretical maximum near-bottom shear stress distribution of the bottom bed under the combined action of waves and tidal currents in Example 2 of the present application;

[0047] Fig.25 This is a schematic diagram of the change in sand content at the time of flooding and resting before and after the ecological restoration of oyster reefs under the combined action of waves and tidal currents in Example 2 of the present application;

[0048] Fig.26This is a schematic diagram of the change in the direction of residual sand transport of the oyster reef sand capture effect under the combined action of waves and tidal currents in Example 2 of the present application;

[0049] Fig. 27 This is a schematic diagram of the change in residual sand transport intensity of the oyster reef sand capture effect under the combined action of waves and tidal currents in Example 2 of the present application;

[0050] Fig.28 This is a schematic diagram of the changes in tidal flat landforms after 5 years in Scenario 1 of Example 2 of the present application;

[0051] Fig.29 This is a schematic diagram of the changes in tidal flat landforms in Scenario 2 of Example 2 of the present application after 5 years;

[0052] Fig.30 This is a schematic diagram of the changes in tidal flat landforms after 5 years in Scenario 3 of Example 2 of the present application;

[0053] Fig.31 This is a schematic diagram of the changes in tidal flat landforms after 5 years in Scenario 4 of Example 2 of the present application. DETAILED DESCRIPTION

[0054] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0055] Example 1

[0056] It is worth mentioning that the sediment in the tidal flat area is mostly transported in the form of suspended sediment. In the existing ecological restoration methods, the method of simulating the movement of suspended sediment on the coast mostly uses uniform sand (i.e. single particle size) to represent the bottom distribution of the entire area, and then selects the formula of cohesive sand or non-cohesive sand for calculation. However, the bottom sediment in the tidal flat area is mostly non-uniform sand composed of clay, silt and fine sand. When the non-uniformity of the bottom sediment is high, it is unreasonable to use the formula of uniform sand to simplify and study the movement of non-uniform sand, because the scouring of sediment particles is different from that of uniform sand and the sediment movement is more complex and changeable, and the error is large. This embodiment establishes a non-uniform sediment dynamic geomorphology model, considers the non-uniform sand critical erosion shear stress of viscosity, bottom bed density and shielding-exposure effect, the vertical distribution of suspended sand of different particle sizes, the interference-flocculation sedimentation effect and the vertical sediment stratification of the bottom bed buffer layer-transport layer-storage layer and other coupling factors, optimizes the calculation method of the non-uniform sand source and sink terms in the model, reflects the comprehensive effects of the initiation, sedimentation and bottom bed consolidation of sediments with different grades, effectively improves the simulation accuracy of the continuous change of tidal flat topography under different scenario simulations, and improves the restoration effect of the ecological restoration of tidal flats after reclamation using oyster reefs and the evaluation accuracy of the restoration effect.

[0057] In detail, a certain beach after reclamation is taken as an example. A non-uniform sediment dynamic geomorphological model of the oyster reef influence area is constructed for the beach after reclamation. Specifically, a hydrodynamic model, a sediment model and a geomorphological model are constructed. Real-time data exchange can be carried out between different models to achieve coupling between different physical processes, so that the ecological restoration simulation of the beach after reclamation is closer to the actual situation, so that the implementation can achieve better restoration effects.

[0058] Please refer to Figure 1-Figure 31 The present application provides an oyster reef ecological restoration method based on tidal flats after sea reclamation, which is executed by a controller and includes:

[0059] First, the tidal field enclosure in the target area is divided into ecological restoration areas: the specific implementation of the ecological restoration area division for the tidal field enclosure in the target area is: according to the direction and movement pattern of waves and water currents in the study area, the west and east sides are determined to be closed boundaries, the north side is closed boundary with land, and the south side is an open boundary. Figure 2 As shown, it should be noted that the tidal current field in the sea area of ​​a certain beach is a reciprocating flow, and the flow direction is basically perpendicular to the coastline. Based on this, the above area is divided into target areas. This setting takes into account the most dangerous wave-current coupling conditions, and thus more accurately improves the ecological restoration effect of oyster reefs.

[0060] Next, obtain the layout of the oyster reefs in the ecological restoration area: The specific method of obtaining the layout of the oyster reefs in the ecological restoration area is as follows: According to the water flow characteristics of the target area, determine that three oyster reef belts are set at intervals. Specifically, determine to use 1m*1m*1m alloy net bag oyster reefs. 1500 alloy net bag oyster reefs are arranged to form an oyster reef belt. According to the wave height characteristics of the study area and the principle of Bragg resonance, set three oyster reef belts at intervals of 40m. This can more effectively experiment the wave-breaking effect of oyster reefs. Three oyster reef belts are set at intervals of 40m. Figure 3 As shown in the figure, three oyster reef belts are arranged in a rectangular area parallel to the coastline, and are arranged about 850m outside the main dike of a certain period of a certain beach. Each oyster reef belt is a 10m×150m rectangular area, and each area is composed of 1500 1m×1m×1m unit oyster reef bodies. Furthermore, due to the small implementation scope of the oyster reef design scheme, it is necessary to encrypt the established numerical model of the sea area of ​​a certain beach, and the grid size after the front edge encryption of a certain period is about 10m. The terrain elevation caused by the reef body and the roughness of the reef body itself will affect the hydraulic resistance. The roughness of the oyster reef area is taken as 0.035 and the tidal flat area is taken as 0.02. Optionally, the oyster reef can also be a cube, a cone, etc.

[0061] Next, establish a non-uniform sediment dynamic model for the target area: the construction process of the non-uniform sediment dynamic model is: construct a hydrodynamic model and a sediment model, and integrate the non-uniform sand parameters into the hydrodynamic model and the sediment model to form a non-uniform sediment dynamic model. The hydrodynamic model includes: simulating tidal flat waves, wherein the wave frequency is 15%, the effective wave height is 0.5m, and the spectral peak period is 5.7s. The wave direction considers the most unfavorable situation, that is, perpendicular to the shoreline direction. The wave calculation adopts the open source third-generation wave SWAN model, namely the Delft 3D-WAVE module, and the SWAN model uses a two-dimensional dynamic spectrum density. To describe the randomness of wave propagation, consider the physical processes of refraction, reflection and bottom friction of shallow water waves and wave breaking caused by shallow water depth, as well as the white hat effect and nonlinear wave-wave interaction (three waves or four waves). The dynamic spectrum balance equation is:

[0062]

[0063] Where: , , and Represents x, y, and The wave propagation speed in space; S is the source and sink term expressed as spectral density.

[0064] It should be noted that the hydrodynamic model considers the combined effect of tides and waves when simulating tidal flat waves. The tide is calculated using the M2 tidal component and is obtained from a large range of tides. The tidal analysis is based on the vertical integration of the NS equations of incompressible fluids. The continuity equation and momentum conservation equation in the orthogonal curvilinear coordinate system are as follows:

[0065]

[0066]

[0067]

[0068] Where: is time(s); , is the orthogonal curvilinear coordinate (m); , are the Lamé coefficients for the Cartesian and curvilinear coordinate transformations; , They are , Direction: the average velocity component along the water depth (m / s); is the tide level (m); is the still water depth (m); is the total water depth (m); is the Coriolis force coefficient (s-1), is the geostrophic angular velocity, To calculate the latitude of a body of water; is the acceleration due to gravity (m / s 2 ); is the water density (kg / m3); , , , is the turbulent shear stress (N / m 2 ); , is the surface wind stress (N / m 2 ); , is the bottom bed resistance (N / m 2 ); , Stress imposed by external processes, such as wave radiation stress, etc. (N / m 2 ). Turbulent shear stress , , , To parameterize in the form of eddy viscosity coefficient, it can be expressed as:

[0069]

[0070]

[0071]

[0072] Where: is the turbulent viscosity coefficient (m 2 / s), which can be taken as a constant. The present application adopts a non-uniform sand motion calculation model to consider the interaction between cohesive sand and non-cohesive sand and various physical processes.

[0073] It should be noted that in the sediment model, the vertical average convection-diffusion equation for suspended sediment transport is:

[0074]

[0075] In the formula, is the sand content of the ith component; and represents the horizontal sediment diffusion coefficient in the x and y directions; It is a source-sink term, characterizing the suspension and sedimentation flux of bottom sediment.

[0076] Then, the geomorphic model of the target area is established, in which the bed deformation control equation is:

[0077]

[0078] Where: is the sediment settling velocity, c is the sediment content, is the porosity of the bottom bed. Since landform changes have a cumulative effect, the actual update speed is much slower than the speed of tidal and wave changes, and has a significant lag. Therefore, when simulating long-term and large-scale landform evolution, the calculation efficiency of landform update using single-step calculation is low, and the landform acceleration factor (Morphological factor, f mor ) method can accelerate the simulation of landform evolution. That is, for each time step, the net sediment transport rate generated in each grid control volume is multiplied by a coefficient f mor , expand the terrain changes within the grid control volume mor times, thus affecting the water flow and sediment transport in the next time step. The geomorphic acceleration factor method can achieve the effect of accelerating geomorphic simulation. Among them, the geomorphic acceleration factor needs to be used in conjunction with the generalized open boundary conditions (representing tides and waves), and f needs to be reasonably determined through sensitivity analysis. mor size.

[0079] Then, the non-uniform sediment dynamic model was integrated with the geomorphic model to establish a non-uniform sediment dynamic geomorphic model. A dynamic geomorphic numerical model of non-uniform sand movement was established and verified, which effectively improved the simulation accuracy of continuous changes in tidal flat topography at an engineering scale.

[0080] Then, a scenario simulation is determined based on at least the tidal action, wave action, and oyster reef action, and the scenario simulation is input into the non-uniform sediment dynamic geomorphology model to obtain the restoration result. The scenario simulation is at least 4 types: tidal action simulation only, tidal-wave action simulation, tidal-oyster reef action simulation, and tidal-wave-oyster reef action simulation. Please refer to Figure 4 As shown in the table, at least 4 scenarios are set and input into the non-uniform sediment dynamic geomorphology model for ecological restoration simulation. Scenario 1 is the tidal action only, scenario 2 is the tidal-wave action, scenario 3 is the tidal-oyster reef action, and scenario 4 is the combined action of tidal-wave-oyster reef.

[0081] Finally, the restoration effect is evaluated: the restoration effect evaluation is specifically as follows: the restoration result parameters obtained in the scenario with only tidal action are used as benchmark parameters, and the restoration result parameters in other scenarios are compared with the benchmark parameters to evaluate the restoration effect. Among them, the flow velocity, wave height, wave height attenuation coefficient, maximum near-bottom shear stress, peak sediment content, peak value of reduced sediment content, net sediment transport direction, and siltation intensity before and after the oyster reef are set for the above four scenarios to determine the restoration effect.

[0082] It should be noted that the simulation time of the non-uniform sediment dynamic geomorphology model is set to 7 days, and the tidal velocity, wave height, sand content, and residual sediment transport parameters at the characteristic moments are calculated respectively. The above parameters are used to evaluate the flow blocking effect of oyster reefs and their sediment capture effect. The geomorphology model sets the acceleration factor to 60, and the acceleration factor is set to 60 in the geomorphology model to simulate the 5-year geomorphological evolution of the tidal flat area under four different scenarios. By comparing with scenario 1, scenario 1 is the state of the target area under the action of tides without oyster reefs, and then determine the impact of oyster reef restoration measures on tidal flat landforms. The present application also solves the problem that the prior art cannot effectively evaluate the ecological restoration effect of oyster reefs on tidal flats after sea reclamation.

[0083] Example 2

[0084] Please refer to Figure 1-Figure 31 Taking a certain beach after reclamation as an example, a non-uniform sediment dynamic geomorphic model of the oyster reef impact area is constructed for the beach after reclamation by constructing a hydrodynamic model, a sediment model and a geomorphic model. This embodiment simulates the ecological restoration of a certain beach after reclamation and evaluates the ecological restoration effect.

[0085] First, scenario 1 with only tidal currents and scenario 3 with tidal currents and oyster reefs were simulated in the heterogeneous sediment dynamic geomorphology model, and the following results were obtained:

[0086] refer to Figure 5 and Figure 6 , Figure 5 Schematic diagram of the difference in water flow velocity with and without oyster reefs during rapid flooding. Figure 6 The figure is a schematic diagram of the difference in water flow velocity with and without oyster reefs during rapid ebbs. It can be seen that under rapid ebbs and flows, the influence of oyster reefs on tidal velocity in the target area is within 0.1m / s, and the range is limited to within 2km around the oyster reef area. The water flow velocity of the oyster reef and its shelter area is weakened, while the water flow velocity in the areas on both sides is enhanced. The velocity change of rapid ebbs is stronger than that of rapid ebbs, which is due to the fact that the velocity of rapid ebbs is greater than that of rapid ebbs.

[0087] Please refer to Figure 7 and Figure 8 Under the action of pure tidal current, the ecological restoration of the tidal flat after reclamation was simulated by setting up oyster reefs. Figure 7 Schematic diagram of flow velocity distribution after oyster reef ecological restoration under the action of pure tidal current during rapid rise. Figure 8 This is a schematic diagram of the velocity distribution after ecological restoration of oyster reefs under the action of pure tidal currents during rapid ebbs and flows. From the velocity distribution characteristics, it can be seen that the velocity between oyster reefs is significantly lower than that in the surrounding sea areas, and is less than 0.1 m / s during rapid rise and fall. The velocity on the north and south sides of the oyster reefs is relatively large, reaching 0.3 m / s during rapid rises and about 0.2 m / s during rapid ebbs.

[0088] Please refer to Fig. 9 and Fig.10 , respectively, are the differences in velocity magnitude and velocity direction after oyster reef ecological restoration under pure tidal action. Fig. 9 Schematic diagram of the difference in flow velocity before and after oyster reef ecological restoration under the action of pure tidal current during rapid rise. Fig.10 This is a schematic diagram of the difference in flow velocity before and after ecological restoration of oyster reefs under the action of pure tidal currents during rapid falls. It can be seen from the figure that the flow blocking effect of oyster reefs is more obvious. The flow velocity in the oyster reef area is reduced by about 0.1~0.2m / s. There are large areas of increased flow velocity on both sides of the oyster reef, and the increased impact can affect the northern shore of the oyster reef area.

[0089] Please refer to Fig.11 and Fig.12 , Fig.11 Schematic diagram of the difference in tidal flow direction after oyster reef ecological restoration under the action of pure tidal current during rapid rise. Fig.12 This is a schematic diagram of the difference in tidal flow direction after the ecological restoration of the oyster reef under the action of pure tidal currents during rapid ebbs. It can be seen that the impact of oyster reefs on tidal flow direction is mainly limited to the surrounding local sea areas.

[0090] Please refer to Fig.13 and Fig.14 , before and after the oyster reef ecological restoration measures were set up, the distribution characteristics of sand content during the flood and rest periods were as follows: Fig.13 The distribution map of sediment content at the time of ups and downs without oyster reefs in the target area under the action of pure tidal current. Fig.14 This is the distribution map of sediment content when there are oyster reefs in the target area under the action of pure tidal currents.

[0091] Please refer to Fig.15 , which is a graph showing the change of sediment content at the time of flooding and resting before and after the ecological restoration of oyster reefs. It can be seen from the figure that at the time of flooding (high tide), there is a peak sediment content area in front of a certain period of dam, with a peak value of 0.4kg / m 3 After the construction of oyster reef ecological restoration measures, the peak sediment content and its range in the protected nearshore area increased significantly, with the maximum increase reaching 0.06kg / m 3 The sand content in the area between the three oyster reef belts decreased slightly, with a small decrease of about 0.01 kg / m 3 The reason why the sediment content between oyster reefs decreases is that the oyster reefs have a greater obstruction effect, which leads to the weakening of the water flow dynamics between oyster reefs and the weakening of the water body's sand-carrying capacity. Therefore, the suspended sediment content decreases and the sediment is more likely to silt and settle.

[0092] Please refer to Fig.16 and Fig.17 , Fig.16 Schematic diagram of the change of residual sand transport direction of oyster reef sand capture effect under pure tidal action. Fig.17 The diagram is a schematic diagram of the change in the residual sand transport intensity of the oyster reef sand capture effect under the action of pure tidal currents. Under the action of pure tidal currents, the area with the largest change in the net sand transport direction after the oyster reefs are between the oyster reefs and the nearshore area shielded by the oyster reefs. The net transport changes from the shoreward transport before the project to parallel to the oyster reef direction, and the intensity of the net sand transport changes within ±1kg / s / m.

[0093] Then, scenario 2 of tide-wave action and scenario 4 of tide-wave-oyster reef combined action were respectively brought into the non-uniform sediment dynamic geomorphology model for simulation, and the simulation results were compared with those of scenario 1 and scenario 3, and the following restoration results were obtained:

[0094] Please refer to Fig.18 , Fig.19 , Fig. 20 , Fig.21 , the tidal-wave scenario 2 is brought into the non-uniform sediment dynamic geomorphology model for simulation: Fig.18 Schematic diagram of the effect of waves on the flow resistance of oyster reefs during rapid rise. Fig.19 Schematic diagram of the effect of waves on the flow resistance of oyster reefs during rapid fall. Fig. 20 Schematic diagram of the flow-blocking effect of oyster reefs under the coexistence of waves and currents and pure tidal currents during rapid rise. Fig.21 This is a schematic diagram of the flow-blocking effect of oyster reefs under the coexistence of waves and currents and the action of pure tidal currents during rapid falls. It can be seen from the figure that under the action of onshore waves, the contribution of waves to the flow-blocking effect of oyster reefs is more obvious during rapid falls, which is mainly manifested in the weakening of the nearshore flow velocity around the oyster reef and the sheltered area, but a slight increase in the nearshore flow velocity on the north side of the oyster reef area. The impact on the flow direction is concentrated in a small area near the oyster reef.

[0095] Please refer to Fig. 22 Since the oyster reef ecological restoration measures are set up in the high beach area, they will only be partially submerged by the tide under the action of high water level. Therefore, in order to compare the wave dissipation characteristics of oyster reefs, we specially selected high water level to compare the wave height change and wave height attenuation coefficient with and without oyster reefs. Fig. 22 , Fig. 22 is the wave height change value under the combined action of waves and tides (without oyster reefs and with oyster reefs). It can be seen that the oyster reef has a more obvious wave-breaking effect, especially in the area protected by the oyster reefs, where there is obvious wave height attenuation. The closer to the oyster reef, the more obvious the wave height attenuation, with the maximum attenuation exceeding 0.2m. After the oyster reef is set up, the maximum attenuation of the nearshore wave height can reach 0.1m.

[0096] Please refer to Fig.23 As can be seen from the figure, in the rectangular area formed by the oyster reef and the nearshore coastline, the wave height attenuation coefficient is between 0.2 and 0.8. Among them, the wave attenuation coefficient on the side close to the oyster reef can reach 0.2, and the wave elimination effect is significant. The wave attenuation coefficient on the nearshore side is about 0.4-0.6. Since the oyster reef ecological restoration measures are set in the high beach area, they will only be partially submerged by the tide under the action of high water levels. To compare the wave elimination characteristics of oyster reefs, we specially selected high water levels to compare the wave height changes and wave height attenuation coefficients with and without oyster reefs.

[0097] Please refer to Fig.24 , Fig.24 It is the theoretical maximum near-bottom shear stress under the combined action of waves and tides. It should be noted that this maximum near-bottom shear stress only exists at high tide. It can be seen that the shear stress at both ends of the oyster reef is relatively large, reaching 1.5~2.0 Pa. In the oyster reef and the nearshore rectangular area it shields, the theoretical maximum near-bottom shear stress is significantly reduced to 0.3 Pa compared with the surrounding area.

[0098] Please refer to Fig.25 , Fig.25 This is a comparison of the changes in sediment content at high and low times before and after the oyster reef ecological restoration measures were set up under the combined action of waves and tides. Fig.13 and 14 Under the combined effects of waves and tides, the sediment content between the three oyster reef belts and in the western coastal areas they sheltered showed a decreasing trend. The peak of the sediment content reduction was located between the oyster reefs and in the nearby waters, with a reduction of more than 2 kg / m3 The sand content in the eastern offshore area and the eastern coastal area protected by oyster reefs showed an increasing trend, and the peak of the increase occurred in the eastern coastal area covered by oyster reefs, with an increase of 1kg / m 3 Compared with the pure tidal current, the increase in sediment content in the peripheral area is due to the increase in power causing local scouring; the oyster reef shelter area has a reduced power and the sand-carrying capacity of the water flow is reduced, so the sediment content decreases, causing sediment deposition.

[0099] Please refer to Fig.26 , Fig. 27 , Fig.26 Schematic diagram of the change of residual sediment transport direction of oyster reef sand capture effect under the coexistence of waves and currents. Fig. 27 Schematic diagram of the change of residual sediment intensity of oyster reef sand capture effect under the coexistence of waves and currents. Fig.16 and Fig.17 , Fig.26 and Fig. 27 The net sediment transport diagram with and without oyster reefs under the combined action of waves and currents can be compared to analyze the sand-catching effect of oyster reefs. Under the combined action of waves and currents, when there are oyster reefs, the net sediment transport direction around the oyster reefs is directed to the oyster reefs; from the perspective of the intensity of net sediment transport, the net sediment transport intensity increases on the north and south sides of the oyster reefs and the areas surrounded by the coastline, but the net transport decreases in the sea area outside the oyster reefs as a whole. It can be seen that the sand-catching effect of oyster reefs is more obvious when considering the combined action of waves and tides. This is because the net sediment transport rate of the oyster reef area under the action of waves and currents is greater than the net sediment transport rate under the action of pure tides (waves stir up sediments), and at the same time, the power of oyster reefs and their sheltered areas is weakened, which is easy to form a large amount of sediment accumulation, making the surrounding areas of oyster reefs and nearshore areas a "sedimentation sink" for sediment, that is, the overall sand-catching effect of oyster reefs shows a trend of gathering from high-energy areas to low-energy areas, eroding and suspending in high-energy areas, and settling and silting in low-energy areas.

[0100] In summary, the sand-catching effect of oyster reefs is more obvious under the combined action of waves and tides. The study found that the net sediment transport rate of the oyster reef area under the action of waves and currents is greater than the net sediment transport rate under the action of pure tides (waves stir up sediments). At the same time, the power of oyster reefs and their sheltered areas is weakened, which is easy to form a large amount of sediment accumulation, making the surrounding areas of oyster reefs and nearshore areas a "sedimentation sink" for sediments, that is, the overall sand-catching effect of oyster reefs shows a trend of gathering from high-energy areas to low-energy areas, eroding and suspending in high-energy areas, and settling and silting in low-energy areas.

[0101] Finally, scenarios 1, 2, 3, and 4 were introduced into the non-uniform sediment dynamic geomorphology model to simulate the restoration effect in the next five years, and the following restoration results were obtained:

[0102] Depend on Fig.28It can be seen that under the action of pure tidal currents, the nearshore waters show a sedimentation trend regardless of the presence or absence of oyster reefs. In the absence of oyster reefs, the nearshore sedimentation intensity is about 0.01-0.02 m / yr. Fig.29 It can be seen that when there are oyster reefs, the siltation intensity in the area around the oyster reefs can increase to 0.05m / yr, but the siltation intensity in the sea area north of the oyster reefs is basically unaffected. Fig.30 , Fig.31 It can be seen that when the combined effects of tides and waves are taken into account, the nearshore situation changes from a micro-silting situation under the action of pure tides to a micro-scouring situation, with an annual scouring rate of 0.02-0.04m / yr. However, after considering the effect of oyster reefs, the scouring range in the open sea is reduced and the scouring intensity is weakened. There is a more obvious silting situation around the oyster reefs and in the covered nearshore areas, with a silting intensity of up to 0.1m / yr and an average of about 0.05m / yr. The silting intensity in the nearshore area covered by oyster reefs is about 0.025m / yr.

[0103] It is worth noting that although the maximum near-bottom shear stress in the local areas at both ends of the oyster reef is 1.5-2Pa under the combined action of waves and tides, which is greater than that in the oyster reef area, no obvious scouring occurs. Figure 28-Figure 31 This is because the shear stress is a characteristic value at the high tide moment and lasts for a short time in the tidal cycle, so the amount of sediment scouring generated is small. In addition, combined with the net sediment transport trend in the oyster reef area, it can be seen that the net sediment transport intensity in the area surrounding the oyster reef is relatively large, and it has become a "sedimentation sink" for sediment, with sufficient sediment supply. Therefore, in the 5-year topographic change simulation, although the sedimentation intensity in the area surrounding the oyster reef increased, there was no obvious scouring and silting trend at both ends of the oyster reef. After the oyster reef restoration was implemented, the net sediment transport direction pointed to the oyster reef area, resulting in obvious sediment deposition in the oyster reef area. After considering the wave action, the area sheltered by the oyster reef is mainly the rectangular sea area formed by it and the coast, and the hydrodynamic intensity is significantly smaller than that of the surrounding sea area, which makes it easy for sediment to accumulate in this sea area and form sediment deposition. Whether considering only the tidal current or the combined effects of waves and tidal currents, there is an obvious siltation trend around the oyster reef and its sheltered nearshore areas, with the siltation affecting about 260m onshore and about 170m offshore, with the maximum siltation thickness of 0.5m.

[0104] In summary, based on the tidal flat after reclamation, the oyster reef ecological restoration method provided in this embodiment, by constructing a hydrodynamic model, a sediment model and a geomorphic model and integrating them to establish a non-uniform sediment dynamic geomorphic model, specifically, different models can exchange data in real time, realize the coupling between different physical processes, so that the ecological restoration simulation of a certain beach after reclamation is closer to the actual situation. In this method, under the action of pure tidal current, the influence of oyster reefs on tidal currents is mainly limited to the surrounding local sea areas, the flow velocity in the oyster reef area decreases, and the flow velocity on both sides increases. After coupling the wave action, the influence of waves on the flow blocking effect of oyster reefs is mainly to reduce the flow velocity in the surrounding and sheltered areas when falling rapidly. Under high water levels, the wave height in the oyster reef sheltered area is significantly attenuated, and the attenuation coefficient is between 0.2 and 0.8. It can be seen that the flow blocking and wave elimination effects of oyster reefs in the restoration method provided by this application are more obvious. On the other hand, waves can cause the scouring of the outer sea area of ​​oyster reefs to intensify, resulting in an increase in the sand content, while the flow blocking and wave-breaking effects of the oyster reef-sheltered area weaken the hydrodynamics, reduce the sand-carrying capacity of the water flow, and cause the sediment to fall. In addition, the sand-catching effect of oyster reefs produces a net transport of sediment directed to the oyster reefs, increasing the net transport intensity of sediment around the oyster reefs and nearshore areas, making the oyster reef area and the nearby sea area a sediment collection area. A five-year restoration simulation of oyster reef ecological restoration was conducted. Under the action of tidal currents alone, oyster reefs increased the siltation intensity of the surrounding sea area by 2.5 to 5 times, affecting about 260m of shoreward siltation and about 190m of offshore siltation. When the coupling effects of tidal currents and waves are considered, there is a more obvious siltation trend around the oyster reefs and the nearshore areas they shelter, with a siltation intensity of up to 0.1m / yr, an average of about 0.05m / yr, and a siltation intensity of about 0.025m / yr in the nearshore areas sheltered by oyster reefs. The siltation range does not change much compared with the simple tidal action, and other areas become slightly impacted. The ecological restoration method provided by this embodiment solves the problem that the existing technology cannot effectively use oyster reefs to achieve ecological restoration of tidal flats after sea reclamation. At the same time, this application also solves the problem that the existing technology cannot effectively evaluate the ecological restoration effect of oyster reefs on tidal flats after sea reclamation.

[0105] The above description is only a preferred implementation mode of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. A method for ecological restoration of oyster reefs based on tidal flats after sea reclamation, the method being executed by a controller and characterized in that: include: Demarcate the target area tidal field and implement ecological restoration area division; Obtain the location of oyster reefs in the ecological restoration area; Establish a non-uniform sediment dynamic model for the target area; Establish a geomorphic model of the target area; The non-uniform sediment dynamic model is integrated with the landform model to establish a non-uniform sediment dynamic landform model. The construction process of the non-uniform sediment dynamic model is: constructing a hydrodynamic model and a sediment model, and integrating the non-uniform sand parameters with the hydrodynamic model and the sediment model to form a non-uniform sediment dynamic model; wherein: In the hydrodynamic model, the open source third-generation wave SWAN model is used, which at least considers the refraction, reflection and bottom friction of shallow water waves and the physical process of wave breaking caused by shallow water depth, and also considers the white hat effect and nonlinear wave-wave interaction. The dynamic spectrum balance equation is: ； Where: , , and Respectively represent , , and The speed of wave propagation in space; represents the wave group velocity; S is the source and sink term expressed as spectral density; The hydrodynamic model takes into account the combined effects of tides and waves when simulating tidal flat waves. The tide is calculated using the M2 tidal component and a large range of tides. The tidal analysis is based on the vertical integration of the NS equations of incompressible fluids. The continuity equation and momentum conservation equation in the orthogonal curvilinear coordinate system are: ； ； ； Where: For time; , are orthogonal curvilinear coordinates; , are the Lame coefficients of the Cartesian and curvilinear coordinate systems; U and V are , Direction: the component of current velocity averaged along the water depth; is the tide level; is the still water depth; is the full water depth; is the Coriolis force coefficient, is the geostrophic angular velocity, To calculate the latitude of a body of water; is the acceleration due to gravity; is the water density; , , , is the turbulent shear stress; , is the surface wind stress; , is the bottom bed resistance; , Stress imposed by external processes; turbulent shear stress , , , To parameterize in the form of eddy viscosity coefficient, the formula is: ； Where: is the turbulent viscosity coefficient; In the sediment model, suspended sediment transport is calculated using the vertically averaged convection-diffusion equation, which is: ； In the formula, For the The sand content of the components; and represent , Horizontal sediment diffusion coefficient in the direction; is the source-sink term, representing the suspension and settling flux of bottom sediment; At least according to the tidal action, wave action, and oyster reef action, the scenario simulation is determined, and the scenario simulation is input into the non-uniform sediment dynamic geomorphology model to obtain the restoration result, wherein the scenario simulation is at least 4 types: tidal action simulation only, tidal-wave action simulation, tidal-oyster reef action simulation, tidal-wave-oyster reef action simulation; the restoration effect is evaluated specifically as follows: the restoration result parameters obtained from the tidal action scenario alone are used as the benchmark parameters, and the restoration result parameters under other scenarios are compared with the benchmark parameters to evaluate the restoration effect, wherein the flow velocity, wave height, wave height attenuation coefficient, maximum near-bottom shear stress, sediment content peak value, sediment content reduction peak value, sediment net transport direction, and sedimentation intensity before and after the oyster reef are set for the above 4 scenarios are compared to determine the restoration effect; Perform an evaluation of the repair effectiveness.

2. The ecological restoration method according to claim 1, characterized in that: The ecological restoration area division for enclosing the tidal field of the target area is specifically: division according to the flow direction and movement pattern of waves and water flow in the target area.

3. The ecological restoration method according to claim 1, characterized in that: The specific method of obtaining the layout position of the oyster reef in the ecological restoration area is as follows: according to the water flow characteristics of the target area, three oyster reef belts are determined to be arranged in an interval manner.

4. The ecological restoration method according to claim 1, characterized in that: The hydrodynamic model includes: simulating tidal flat waves, wherein the wave frequency is 15%, the effective wave height is 0.5m, and the spectrum peak period is 5.7s.

5. The ecological restoration method according to claim 1, characterized in that: The simulation time of the non-uniform sediment dynamics model is 7 days.

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