Intertidal zone repairing method based on dredged soil microtopography remodeling

Abstract

The invention provides an intertidal zone repairing method based on dredged soil microtopography remodeling. The intertidal zone repairing method comprises the following steps that (1) a submerged dike is built in an offshore intertidal zone; (2) the dredged soil is uniformly thrown and filled in an offshore beach, and the dredged soil is self-balanced and dispersed between the offshore beach and the submerged embankment under the action of ocean water power and tide; and (3) the inshore beach is filled with the restoration composition, and ecological protection and restoration of the ocean shoreline are completed through the water and sand combined action. The remediation composition comprises grass seeds and sandy soil. According to the method, self-balancing dispersion and water-sand comprehensive effects are integrated, the repairing effect of an intertidal zone can be remarkably improved, the stability of a beach face is improved, and the wave scouring condition is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of marine shoreline ecological restoration, and particularly relates to an intertidal zone restoration method based on dredged soil microtopography reshaping. Background Art

[0002] The intertidal zone refers to the shallow beach area between the high tide line and the low tide line. This special area is sea at high tide and land at low tide, with unique environmental characteristics of "seemingly not sea, seemingly not land". As a special ecological transition zone between the sea and the land, the intertidal zone plays an irreplaceable role in the global marine ecosystem.

[0003] From an ecological perspective, the intertidal zone is one of the most productive ecosystems globally, and its ecological service value per unit area even exceeds that of tropical rainforests and coral reef ecosystems. The high light level in the intertidal zone provides ideal conditions for the photosynthesis of algae and vegetation. The plankton, marine bioclastic debris brought by the rising tide, and the nutrients transported by land rain and rivers together constitute a rich food web foundation, supporting a diverse biological community including benthic organisms, fish, shrimps, crabs, etc. In addition, the intertidal zone also has an important coastal protection function, which can effectively buffer wave energy and reduce coastal erosion; it is also an important "blue carbon" sink and plays a key role in the global carbon cycle. That is, this area of the intertidal zone not only has extremely high biodiversity but also plays a key role in coastal protection, carbon sequestration, and material cycling.

[0004] However, in recent years, the intertidal zone ecosystem has been suffering unprecedented damage. On the one hand, the acceleration of coastal urbanization, engineering activities such as land reclamation and port construction have directly occupied and damaged a large amount of intertidal zone habitats; on the other hand, human activities such as overfishing and pollution discharge have led to a sharp decline in the biodiversity of the intertidal zone.

[0005] According to statistics, intertidal zone wetlands have faced significant degradation in the past. This degradation is not only manifested in the reduction of biological species and quantities but also in the loss of ecosystem functions, such as the decline in coastal protection ability and the weakening of water purification function. Notably, the special hydrological environment of the intertidal zone - the wet-dry alternation caused by periodic tidal changes - makes the ecological restoration of this area face unique technical challenges, and traditional land or marine restoration methods are often difficult to be directly applied.

[0006] Meanwhile, the degradation of the intertidal zone has also brought about a chain of ecological effects. As a key link connecting marine and terrestrial ecosystems, the functional degradation of the intertidal zone will affect both marine and terrestrial ecosystems simultaneously. For example, the decline in intertidal biodiversity will lead to a reduction in marine fish resources that use it as a habitat or food source; while the weakening of the coastal protection function will increase the vulnerability of coastal communities to marine disasters such as storm surges. In addition, the intertidal zone is also an important foraging and resting place for many migratory birds, and its ecological status directly affects the integrity of the global migratory bird routes. Facing such a severe situation, developing scientific and effective intertidal ecological restoration technologies has become an urgent task in the current field of marine ecological protection.

[0007] However, from a technical perspective, intertidal ecological restoration faces multiple challenges. The characteristic of this area being "neither fully sea nor fully land" makes it impossible for ordinary onshore equipment and large laying vessels to effectively enter the construction area. The dynamic hydrographic environment in the intertidal zone - periodic tidal changes, wave action, and complex geological conditions - all pose extremely high requirements for the adaptability and stability of restoration technologies.

[0008] The existence of these technical challenges indicates that there is an urgent need to develop ecological restoration methods that are suitable for the special environment of the intertidal zone. Summary of the Invention

[0009] Aiming at the deficiencies of the existing technology, the purpose of the present invention is to provide an intertidal zone restoration method based on the reshaping of dredged soil microtopography. By separately dumping dredged soil and sandy soil containing grass seeds twice, and through self-balanced dispersion and the comprehensive action of water and sediment, the dredged soil resources from the ocean are used to restore the ocean, which conforms to the concept of resource recycling. During the restoration process, the submerged breakwater reduces the erosion of the wave on the shoreline, and the uniform dispersion of the dredged soil during the self-balanced dispersion process ensures the stability of the shore beach, providing a stable habitat for marine organisms.

[0010] To achieve this purpose, the present invention adopts the following technical solutions:

[0011] The present invention provides an intertidal zone restoration method based on the reshaping of dredged soil microtopography, and the intertidal zone restoration method includes the following steps:

[0012] (1) Build a submerged breakwater in the nearshore intertidal zone;

[0013] (2) Uniformly dump the dredged soil on the nearshore beach, and under the action of marine hydrodynamics and tides, the dredged soil undergoes self-balanced dispersion between the nearshore and the submerged breakwater;

[0014] (3) Dump the restoration composition on the nearshore beach, and through the comprehensive action of water and sediment, complete the ecological protection and restoration of the marine shoreline; the restoration composition includes grass seeds and sandy soil.

[0015] The intertidal zone restoration method based on the reshaping of dredged soil microtopography provided by the present invention has the following advantages:

[0016] First, the submerged breakwater set can reduce the erosion of the wave on the shoreline; second, the dredged soil is filled first, and the dredged soil resources from the ocean are used to feed back and repair the shoreline. Moreover, the dredged soil is beneficial to the stability of the beach. Different from the conventional method, in this application, the dredged soil combines with the marine hydrodynamic force and tidal action to achieve the self-balanced dispersion of the dredged soil between the near shore and the submerged breakwater, with excellent dispersion effect. And during the self-balanced process, it can carry out sufficient material exchange with the marine water environment, so that the seaweeds, microorganisms, etc. in the sea water interact with the coarse particles and organic matter in the dredged soil, not only achieving the effect of dispersing the dredged soil but also the self-repair effect. Compared with directly spreading the dredged soil flat, it not only does not need to consume a large amount of manpower, but also can achieve a better restoration effect; third, after the self-balanced dispersion of the present invention, the sandy soil containing grass seeds is filled again. At this time, the intertidal zone already has the dredged soil resources as the foundation, and then the grass seeds and sandy soil are filled. The sandy soil can play a role in fixing the beach surface and reducing the shoreline erosion. At this time, the grass seeds can better take root and grow on the beach, thus achieving an excellent ecological protection and restoration effect.

[0017] Preferably, in step (1), the submerged breakwater sequentially includes an anti-seepage layer and a breakwater body layer from bottom to top.

[0018] The present invention preferably has the submerged breakwater sequentially including an anti-seepage layer and a breakwater body layer from bottom to top. The anti-seepage layer at the bottom can prevent the water body at the bottom from permeating and interacting, which is beneficial to ensuring the maintenance of the water environment during the self-balanced dispersion and achieving a better intertidal zone restoration effect.

[0019] Preferably, the permeability of the anti-seepage layer is lower than that of conventional concrete and sand and gravel. Generally speaking, it is ≤ 1.0×10 - 13 cm / s. For example, it can be 1.0×10 -13 cm / s, 0.9×10 -13 cm / s, 0.8×10 -13 cm / s, 0.7×10 -13 cm / s, 0.6×10 -13 cm / s, 0.5×10 -13 cm / s, 0.4×10 -13 cm / s, 0.3×10 -13 cm / s, 0.2×10 -13 cm / s or 0.1×10 - 13 cm / s, etc., but not limited to the listed values. Other unlisted values within this range are equally applicable.

[0020] Preferably, the material of the anti-seepage layer includes any one or a combination of at least two of anti-seepage concrete, geotextile, steel plate, cement grouting material or gravel layer. Typical but non-limiting combinations include the combination of geotextile and anti-seepage concrete, the combination of gravel layer and geotextile, the combination of steel plate and anti-seepage concrete, the combination of cement grouting material and anti-seepage concrete, the combination of steel plate and cement grouting material, and the combination of gravel layer and cement grouting material.

[0021] Preferably, the material of the embankment body layer includes crushed stones.

[0022] Preferably, the permeability of the embankment body layer is 1×10 -7 cm / s to 1×10 -10 cm / s. For example, it can be 1×10 -7 cm / s, 0.9×10 -7 cm / s, 0.5×10 -7 cm / s, 0.2×10 -7 cm / s, 1×10 -8 cm / s, 0.9×10 -8 cm / s, 0.8×10 -8 cm / s, 0.5×10 -8 cm / s, 0.2×10 -8 cm / s, 1×10 -9 cm / s, 0.9×10 -9 cm / s, 0.8×10 -9 cm / s, 0.7×10 -9 cm / s, 0.5×10 -9 cm / s, 0.2×10 -9 cm / s or 1×10 -10 cm / s, etc., but not limited to the listed values. Other unlisted values within this range are equally applicable..

[0023] Preferably, the construction location of the submerged dike is between 200 m from the shoreline and 500 m from the shoreline. For example, it can be 200 m, 220 m, 230 m, 250 m, 300 m, 320 m, 350 m, 380 m, 400 m, 420 m, 450 m or 500 m, etc., but not limited to the listed values. Other unlisted values within this range are equally applicable.

[0024] Preferably, the height of the submerged dike is between LWL and HWL, where LWL is the lowest tide level and HWL is the highest tide level.

[0025] Preferably, the height of the anti-seepage layer in the submerged dike is 0.1-1% of the total height of the submerged dike. For example, it can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9% or 1%, etc., but is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0026] Preferably, the water content of the dredged soil in step (2) is 50-150%. For example, it can be 50%, 62%, 73%, 84%, 95%, 106%, 117%, 128%, 139% or 150%, etc., but is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0027] Moreover, the dredged soil in the present invention is dredged soil without dehydration treatment, and the water content is relatively high. Since the self-balanced dispersion method is adopted, the dredged soil can be dumped without dehydration. Compared with other methods of dumping after dehydration and dispersion, the method provided by the present invention does not require the dredged soil to be completely evenly dispersed during dumping, and the restoration of the intertidal zone and the balanced dispersion of the dredged soil can be carried out synchronously during the subsequent self-balanced dispersion process.

[0028] Preferably, the material of the dredged soil includes quartz.

[0029] Preferably, the dredged soil also includes clay.

[0030] Preferably, the dredged soil also contains organic matter.

[0031] Preferably, the content of organic matter in the dredged soil is 4.0-4.5 g / kg. For example, it can be 4.0 g / kg, 4.06 g / kg, 4.12 g / kg, 4.17 g / kg, 4.23 g / kg, 4.28 g / kg, 4.34 g / kg, 4.39 g / kg, 4.45 g / kg or 4.5 g / kg, etc., but is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0032] Preferably, the organic matter in the dredged soil includes any one or at least two combinations of aquatic plant residues, animal remains, microbial decomposition products or humus. Among them, typical but non-limiting combinations are combinations of aquatic plant residues and animal remains, combinations of microbial decomposition products and animal remains, combinations of aquatic plant residues and microbial decomposition products, and combinations of humus and animal remains.

[0033] Preferably, the particle size range of the dredged soil is below 200 μm. For example, it can be 0.1 μm, 0.5 μm, 1 μm, 24 μm, 46 μm, 68 μm, 90 μm, 112 μm, 134 μm, 156 μm, 178 μm, 200 μm, etc., but is not limited to the listed values. Other unlisted values within this range are equally applicable.

[0034] Preferably, the mass ratio of the dredged soil with a particle size below 20 μm is 9 - 12%. For example, it can be 9%, 9.4%, 9.7%, 10%, 10.4%, 10.7%, 11%, 11.4%, 11.7%, 12%, etc., but is not limited to the listed values. Other unlisted values within this range are equally applicable.

[0035] It should be noted that the particle size distribution of the dredged soil in the present invention is crucial for the restoration effect. This is because researchers previously found that the restoration effect of directly dumping the dredged soil was not good. After extensive research, the researchers unexpectedly found that a certain batch of dredged soil had a different restoration effect from other dredged soils and had an excellent restoration effect. In this regard, the researchers explored various factors and finally tested the initial dumped dredged soil raw materials and found that the particle size distribution of the dredged soil with better restoration effect was relatively special. Relevant research verified that the dredged soil with a mass ratio of 9 - 12% of particles with a particle size below 20 μm was relatively friendly to plant biomass and water - sand erosion problems. After screening out too many fine particles and too many coarse particles from the remaining batches of dredged soil and conducting experiments, the research conclusion was verified.

[0036] Regarding the above - mentioned restoration results, the researchers predicted that when the particle size of the fine particles is too large, it is easy to cause more serious water - sand erosion, and the restoration effect is very poor. When the particle size of the fine particles is too small, it is difficult to facilitate the rooting and restoration of plants.

[0037] Preferably, the mass ratio of the dredged soil with a particle size above 75 μm is 25 - 35%. For example, it can be 25%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, etc., but is not limited to the listed values. Other unlisted values within this range are equally applicable.

[0038] The researchers also found that the particle size of the particles above 75 μm in the dredged soil needs to be within the range of 25 - 35% to have a certain compaction effect, play a role in fixing plants, reduce the phenomenon of water - sand erosion, and cooperate with the proportion of fine particles to finally have an excellent restoration effect.

[0039] Preferably, the dumping height of the dredged soil is at a position 0.4 - 0.6 m below the marine datum level. For example, it can be 0.4 m, 0.43 m, 0.45 m, 0.47 m, 0.49 m, 0.52 m, 0.54 m, 0.56 m, 0.58 m or 0.6 m, etc., but is not limited to the listed values. Other unlisted values within this range are equally applicable.

[0040] In the present invention, it is preferred to set the dumping height of the dredged soil at a position 0.4 - 0.6 m below the marine datum level, which has a better restoration effect. Among them, when the beach surface height is relatively high, it is easy to cause some sediment, etc. to exceed the height of the submerged dike, resulting in serious water and sediment erosion, and finally the overall change in the beach surface elevation does not meet the expectations; when the beach surface height is relatively low, the water depth is too high, and the phytoremediation is limited.

[0041] Preferably, the dredged soil is dumped during the ebb tide.

[0042] Preferably, the time for self - balancing dispersion is 90 - 365 days. For example, it can be 90 days, 100 days, 120 days, 150 days, 180 days, 201 days, 222 days, 242 days, 263 days, 283 days, 304 days, 324 days, 345 days or 365 days, etc., but is not limited to the listed values. Other unlisted values within this range are equally applicable.

[0043] Preferably, when dumping in step (2), algae are also mixed into the dredged soil.

[0044] Generally speaking, the seawater in the intertidal zone contains pollutants such as heavy metals and organic substances, and these pollutants will affect the growth of organisms and the restoration of the intertidal zone. In the present invention, it is preferred to mix algae into the dumped dredged soil. On the one hand, the organic matter in the dredged soil is fully recycled. The algae absorb the organic matter in the dredged soil and seawater during the process of self - balancing dispersion for growth, and can absorb part of the heavy metals, playing a role in purifying seawater, thus facilitating the growth of other benthic organisms and plants and improving the restoration effect of the intertidal zone; on the other hand, the algae substances can act synergistically with the dredged soil. The algae itself will also produce viscous substances and plant fiber products. After being mixed with the dredged soil, it can improve the rolling effect of the subsequent dredged soil on the roots of plants, thus being more conducive to the growth of plants and benthic organisms and further improving the restoration effect of the intertidal zone; moreover, the algae can carry out photosynthesis, thus absorbing the energy of sunlight to convert carbon dioxide and water into organic matter, thereby providing food for benthic organisms and synergistically with the subsequent grass - seed - containing composition, providing a basis for the growth of benthic biomass.

[0045] Preferably, the algae include any one or a combination of at least two of Gracilaria lemaneiformis, Undaria pinnatifida, green algae, red algae or brown algae. Typical but non-limiting combinations include the combination of Gracilaria lemaneiformis and Undaria pinnatifida, the combination of green algae and Undaria pinnatifida, the combination of Gracilaria lemaneiformis and green algae, the combination of red algae and Undaria pinnatifida, the combination of Gracilaria lemaneiformis and red algae, and the combination of brown algae and Undaria pinnatifida.

[0046] Preferably, the addition amount of the algae is 0.01-0.1 wt% of the dredged soil. For example, it can be 0.01 wt%, 0.02 wt%, 0.03 wt%, 0.04 wt%, 0.05 wt%, 0.06 wt%, 0.07 wt%, 0.08 wt%, 0.09 wt% or 0.1 wt%, etc., but not limited to the listed values. Other unlisted values within this range are equally applicable.

[0047] Preferably, the plant species of the grass seeds in step (3) include any one or a combination of at least two of Suaeda glauca, Spartina anglica, Spartina alterniflora, Tamarix chinensis or Vitex rotundifolia. Typical but non-limiting combinations include the combination of Suaeda glauca and Spartina anglica, the combination of Spartina anglica and Spartina alterniflora, and the combination of Tamarix chinensis and Vitex rotundifolia.

[0048] Preferably, the particle size range of the sandy soil is 150-5000 mm. For example, it can be 150 mm, 680 mm, 1220 mm, 1760 mm, 2300 mm, 2840 mm, 3380 mm, 3920 mm, 4460 mm or 5000 mm, etc., but not limited to the listed values. Other unlisted values within this range are equally applicable.

[0049] Preferably, the mass ratio of the grass seeds to the sandy soil is 0.8-1:1. For example, it can be 0.8:1, 0.83:1, 0.85:1, 0.87:1, 0.89:1, 0.92:1, 0.94:1, 0.96:1, 0.98:1 or 1:1, etc., but not limited to the listed values. Other unlisted values within this range are equally applicable.

[0050] Preferably, the distribution density of the grass seeds after the dumping in step (3) is 20-30 g / m 2 , for example, it can be 20 g / m 2 , 22 g / m 2 , 23 g / m 2 , 24 g / m 2 , 25 g / m 2 , 26 g / m 2 , 27 g / m 2 , 28 g / m 2 , 29 g / m 2 or 30 g / m 2etc., but not limited to the listed values, and other unlisted values within this range are equally applicable.

[0051] Preferably, the throwing and filling thickness of the repair composition is H, where H ≤ LWL + 0.5 m, and the value range of H is 0.8 - 1.2 m. For example, it can be 0.8 m, 0.85 m, 0.89 m, 0.94 m, 0.98 m, 1.03 m, 1.07 m, 1.12 m, 1.16 m or 1.2 m, etc., but not limited to the listed values, and other unlisted values within this range are equally applicable.

[0052] In the present invention, it is preferred that the throwing and filling thickness H of the repair composition meets the above two requirements, which can ensure both the activity area of benthic organisms and the repair effect of the intertidal zone.

[0053] Preferably, the duration of the comprehensive action of water and sediment is 90 days to 365 days. For example, it can be 90 days, 100 days, 110 days, 120 days, 150 days, 180 days, 200 days, 210 days, 220 days, 230 days, 250 days, 280 days, 300 days, 320 days, 350 days, 360 days or 365 days, etc., but not limited to the listed values, and other unlisted values within this range are equally applicable.

[0054] In the present invention, the comprehensive action of water and sediment in the intertidal zone refers to the interaction between water flow, waves, sediments (sand, mud, salts, etc.) and biological activities. These factors act together to determine the deposition and erosion processes in the intertidal zone, the stability of the ecological environment, the growth of plants and animals, etc. Specifically, the effects of the comprehensive action of water and sediment include the following aspects:

[0055] 1. Sediment transport and accumulation

[0056] The comprehensive action of water and sediment directly affects the transport, accumulation and distribution of sediments in the intertidal zone. The action of water flow and waves will push sand grains and sediment to move within the intertidal zone. These sediments will accumulate in the intertidal zone under certain conditions, forming landforms such as salt flats and tidal flats. The accumulation of sediments provides a basis for the growth of plants and the habitation of animals, and improves the biodiversity of the intertidal zone.

[0057] 2. Influence of tides and water flow

[0058] The tidal action is the core of the comprehensive action of water and sediment in the intertidal zone. The ebb and flow of tides will cause changes in the intensity and direction of water flow, and these water flows will affect the sediment transport, deposition and erosion in the intertidal zone. Different tidal patterns (such as spring tides and neap tides) affect the water flow intensity, the exchange rate of the intertidal zone waters, as well as the distribution of dissolved oxygen and nutrients, which is of great significance for the restoration of the intertidal zone ecosystem.

[0059] 3. Interaction between organisms and sediments

[0060] During the restoration process of the intertidal zone, the presence and activities of organisms (such as plants, animals, microorganisms, etc.) interact with the comprehensive action of water and sediment. For example, intertidal plants (such as reeds, saline-alkali plants, etc.) fix sand through their roots, reducing the erosion of water flow on sediments and helping with sediment accumulation and soil stability. The burrowing and foraging behaviors of animals (such as crabs, shellfish, etc.) also affect the rearrangement and distribution of sediments, thereby affecting the ecological environment of the intertidal zone.

[0061] 4. Ecological restoration and soil improvement

[0062] The comprehensive action of water and sediment can change the hydrological conditions and soil properties of the intertidal zone. Through reasonable restoration measures (such as building ecological dikes in the tidal flat, planting native plants, etc.), the flow direction and speed of water in the intertidal zone can be regulated, promoting sediment deposition and soil improvement, and providing a suitable soil environment for plant growth. The soil in the restored intertidal zone will become more stable, the ecosystem will gradually recover, and biodiversity will increase.

[0063] 5. Nutrient and pollutant cycling

[0064] The comprehensive action of water and sediment not only affects the distribution of sediments but also the cycling of nutrients and pollutants in the intertidal zone. The action of water flow and tides brings nutrients (such as nitrogen, phosphorus, etc.) in the ocean into the intertidal zone, providing for the growth of plants and microorganisms. These plants and microorganisms absorb and transform nutrients, improving water quality and helping to restore the ecological environment of the intertidal zone. At the same time, the comprehensive action of water and sediment also affects the decomposition, transformation, and deposition processes of pollutants, reducing the pollution risk in the intertidal zone.

[0065] 6. Improving intertidal ecological diversity

[0066] Since the comprehensive action of water and sediment can create diverse hydrological, topographical, and biological environments, it provides various habitats for the intertidal zone, promoting plant and animal diversity. For example, some plants can adapt to tidal changes and grow in different water depth areas of the intertidal zone, while animals rely on the habitats provided by these plants. Through reasonable water and sediment management, these habitats can be optimized to promote the restoration and stability of the intertidal ecosystem.

[0067] As a preferred technical solution of the present invention, the intertidal zone restoration method includes the following steps:

[0068] (1) Build a submerged dike in the offshore intertidal zone;

[0069] Among them, the submerged dike successively includes an anti-seepage layer and a dike body layer from bottom to top; the permeability of the anti-seepage layer ≤ 1.0×10 -13cm / s; The material of the anti-seepage layer includes any one or a combination of at least two of anti-seepage concrete, geotextile, steel plate, cement grouting material or gravel layer; The material of the embankment body layer includes gravel; The permeability of the embankment body layer is 1×10 -7 cm / s to 1×10 -10 cm / s; The construction position of the submerged dike is between 200 m from the shoreline and 500 m from the shoreline; The height of the submerged dike is between LWL and HWL, where LWL is the lowest tide level and HWL is the highest tide level; The height of the anti-seepage layer in the submerged dike is 0.1% to 1% of the total height of the submerged dike;

[0070] (2) During ebb tide, the dredged soil and algae are evenly dumped on the nearshore beach. Under the action of ocean hydrodynamic force and tides, the dredged soil undergoes self-balanced dispersion between the nearshore and the submerged dike for 180 to 365 days;

[0071] Among them, the water content of the dredged soil is 50% to 150%; The material of the dredged soil includes quartz; The dredged soil also includes clay; The dredged soil also contains organic matter; The content of organic matter in the dredged soil is 4.0 to 4.5 g / kg; The organic matter in the dredged soil includes any one or a combination of at least two of aquatic plant residues, animal remains, microbial decomposition products or humus; The particle size range of the dredged soil is below 200 μm; The mass proportion of the particle size below 20 μm in the dredged soil is 9% to 12%; The mass proportion of the particle size above 75 μm in the dredged soil is 25% to 35%; The dumping height of the dredged soil is at a position 0.4 to 0.6 m below the marine datum; The algae include any one or a combination of at least two of Gracilaria lemaneiformis, Undaria pinnatifida, green algae, red algae or brown algae; The addition amount of the algae is 0.01% to 0.1 wt% of the dredged soil;

[0072] (3) A repair composition is dumped on the nearshore beach. Through the comprehensive action of water and sand, the ecological protection and restoration of the ocean shoreline are completed; The repair composition includes grass seeds and sandy soil;

[0073] Among them, the plant species of the grass seeds include any one or a combination of at least two of Suaeda salsa, Spartina anglica, Spartina alterniflora, Tamarix chinensis or Vitex rotundifolia; The particle size range of the sandy soil is 150 to 5000 mm; The mass ratio of the grass seeds to the sandy soil is 0.8 to 1:1; The distribution density of the grass seeds after dumping is 20 to 30 g / m 2 ; The dumping thickness of the repair composition is H, where H ≤ LWL + 0.5 m, and the value range of H is 0.8 to 1.2 m; The duration of the comprehensive action of water and sand is 90 to 365 days.

[0074] Compared with the prior art, the present invention has at least the following beneficial effects:

[0075] The intertidal zone restoration method based on the reshaping of dredged soil microtopography provided by the present invention realizes the ecological protection and restoration of the marine shoreline through building a submerged dyke in the offshore intertidal zone and then evenly dumping coarse-grained dredged soil on the nearshore beach, and combining with marine hydrodynamic and tidal actions to achieve the self-balanced dispersion of the dredged soil between the nearshore and the submerged dyke. After the self-balanced dispersion ends, silt containing grass seeds and fine-grained sandy soil are dumped again. Through the comprehensive action of water and sediment, the ecological protection and restoration of the marine shoreline are realized. Among them, the dredged soil resources come from the ocean and return to the ocean for restoration, which conforms to the concept of resource recycling. During the restoration process, the submerged dyke reduces the erosion of the shoreline by waves, and the uniform dispersion of different granularity dredged soil ensures the stability of the shore beach and provides a stable habitat for marine organisms. BRIEF DESCRIPTION OF THE DRAWINGS

[0076] Figure 1 It is a restoration schematic diagram of the intertidal zone restoration method based on the reshaping of dredged soil microtopography provided in Embodiment 1 of the present invention.

[0077] In the figure: 1. Submerged dyke; 2. Dredged soil; 3. Restoration composition. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0078] To facilitate the understanding of the present invention, the following embodiments are listed. Those skilled in the art should understand that the embodiments are only for helping to understand the present invention and should not be regarded as specific limitations on the present invention.

[0079] Embodiment 1

[0080] This embodiment provides an intertidal zone restoration method based on the reshaping of dredged soil microtopography. The intertidal zone restoration method includes the following steps:

[0081] (1) Build a submerged dyke in the offshore intertidal zone;

[0082] Among them, the submerged dyke successively includes an anti-seepage layer and a dyke body layer from bottom to top; the permeability of the anti-seepage layer is lower than that of conventional concrete and sand and gravel (it is 0.8×10 -13 cm / s); the material of the anti-seepage layer is anti-seepage concrete; the material of the dyke body layer includes gravel; the permeability of the dyke body layer is 1×10 -7 cm / s; the construction position of the submerged dyke is between 200 m from the shoreline and 500 m from the shoreline; the height of the submerged dyke is between LWL and HWL, where LWL is the lowest tide level and HWL is the highest tide level; the height of the anti-seepage layer in the submerged dyke is 0.5% of the total height of the submerged dyke;

[0083] (2) During the ebb tide, evenly dump the dredged soil and algae on the nearshore beach. Under the action of marine hydrodynamic and tidal actions, the dredged soil is self-balanced and dispersed between the nearshore and the submerged dyke for 180 days;

[0084] Among them, the water content of the dredged soil is 100%; the material of the dredged soil includes quartz; the dredged soil also includes clay; the dredged soil also contains organic matter; the content of organic matter in the dredged soil is 4.2 g / kg; the organic matter in the dredged soil includes aquatic plant residues, animal remains, microbial decomposition products and humus; the particle size range of the dredged soil is below 200 μm; the mass proportion of the particle size below 20 μm in the dredged soil is 10%; the mass proportion of the particle size above 75 μm in the dredged soil is 30%; the filling height of the dredged soil is at a position 0.5 m below the sea datum; the algae include Gracilaria lemaneiformis and Undaria pinnatifida, and the mass ratio of Gracilaria lemaneiformis to Undaria pinnatifida is 1:1; the addition amount of the algae is 0.05 wt% of the dredged soil;

[0085] (3) Dumping and filling the restoration composition on the nearshore beach, and completing the ecological protection and restoration of the marine shoreline through the comprehensive action of water and sediment; the restoration composition includes grass seeds and sandy soil;

[0086] Among them, the plant species of the grass seeds include Suaeda glauca; the particle size range of the sandy soil is 500 - 1000 mm; the mass ratio of the grass seeds to the sandy soil is 1:1; the distribution density of the grass seeds after dumping and filling is 25 g / m 2 ; the dumping and filling thickness of the restoration composition is H, where H ≤ LWL + 0.5 m, and the value range of H is 1.0 m; the duration of the comprehensive action of water and sediment is 210 days.

[0087] Example 2

[0088] This example provides an intertidal zone restoration method based on the reshaping of the microtopography of dredged soil. The intertidal zone restoration method includes the following steps:

[0089] (1) Construct a submerged dyke in the nearshore intertidal zone;

[0090] Among them, the submerged dyke successively includes an anti-seepage layer and a dyke body layer from bottom to top; the permeability of the anti-seepage layer is lower than that of conventional concrete and sand and gravel, specifically 1×10 -13 cm / s; the material of the anti-seepage layer is an anti-seepage membrane (specifically, geotextile); the material of the dyke body layer includes crushed stones; the permeability of the dyke body layer is 1×10 -10 cm / s; the construction position of the submerged dyke is between 200 m from the shoreline and 500 m from the shoreline; the height of the submerged dyke is between LWL and HWL, where LWL is the lowest tide level and HWL is the highest tide level; the height of the anti-seepage layer in the submerged dyke is 0.8% of the total height of the submerged dyke;

[0091] (2) During ebb tide, the dredged soil and algae are evenly dumped on the nearshore beach. Under the action of ocean hydrodynamic and tides, the dredged soil undergoes self-balanced dispersion between the nearshore and the submerged breakwater for 250 days;

[0092] Among them, the water content of the dredged soil is 150%; the material of the dredged soil includes quartz; the dredged soil also includes clay; the dredged soil also contains organic matter; the content of organic matter in the dredged soil is 4.0 g / kg; the organic matter in the dredged soil includes aquatic plant residues, animal remains, microbial decomposition products and humus; the particle size range of the dredged soil is 1 - 200 μm; the mass ratio of particles with a size of less than 20 μm in the dredged soil is 12%; the mass ratio of particles with a size of more than 75 μm in the dredged soil is 25%; the dumping height of the dredged soil is at a position 0.6 m below the ocean datum; the algae include Gracilaria lemaneiformis and brown algae, and the mass ratio of Gracilaria lemaneiformis to brown algae is 0.8:1; the addition amount of the algae is 0.1 wt% of the dredged soil;

[0093] (3) The restoration composition is dumped on the nearshore beach. Through the comprehensive action of water and sediment, the ecological protection and restoration of the ocean shoreline are completed; the restoration composition includes grass seeds and sandy soil;

[0094] Among them, the plant species of the grass seeds include Spartina anglica and Spartina alterniflora (the mass ratio of the two is 1:1); the particle size range of the sandy soil is 150 - 2000 mm; the mass ratio of the grass seeds to the sandy soil is 0.8:1; the distribution density of the grass seeds after dumping is 30 g / m 2 ; the dumping thickness of the restoration composition is H, where H ≤ LWL + 0.5 m and the value range of H is 0.8 m; the duration of the comprehensive action of water and sediment is 180 days.

[0095] Example 3

[0096] This example provides an intertidal zone restoration method based on the reshaping of the microtopography of dredged soil. The intertidal zone restoration method includes the following steps:

[0097] (1) Build a submerged breakwater in the nearshore intertidal zone;

[0098] Among them, the submerged breakwater sequentially includes an anti-seepage layer and a dyke body layer from bottom to top; the permeability of the anti-seepage layer is lower than that of conventional concrete and sand and gravel, specifically 0.5×10 -13 cm / s; the material of the anti-seepage layer is a combination of steel plates and a gravel layer, where the steel plates are arranged on both sides of the gravel layer; the material of the dyke body layer includes crushed stones; the permeability of the dyke body layer is 1×10 -9cm / s; The construction location of the submerged dike is between 300 m and 500 m from the shoreline; the height of the submerged dike is between LWL and HWL, where LWL is the lowest tide level and HWL is the highest tide level; the height of the anti-seepage layer in the submerged dike is 0.1% of the total height of the submerged dike;

[0099] (2) During the ebb tide, the dredged soil and algae are evenly dumped on the nearshore beach. Under the action of ocean hydrodynamic and tides, the dredged soil undergoes self-balanced dispersion between the nearshore and the submerged dike for 365 days;

[0100] Among them, the water content of the dredged soil is 50%; the material of the dredged soil includes quartz; the dredged soil also includes clay; the dredged soil also contains organic matter; the content of organic matter in the dredged soil is 4.5 g / kg; the organic matter in the dredged soil includes aquatic plant residues, animal remains, microbial decomposition products and humus; the particle size range of the dredged soil is 1 - 200 μm; the mass ratio of the particle size below 20 μm in the dredged soil is 9%; the mass ratio of the particle size above 75 μm in the dredged soil is 35%; the dumping height of the dredged soil is at a position 0.4 m below the marine datum; the algae include red algae and brown algae, and the mass ratio of Gracilaria lemaneiformis and brown algae is 1.2:1; the addition amount of the algae is 0.01 wt% of the dredged soil;

[0101] (3) The repair composition is dumped on the nearshore beach. After the comprehensive action of water and sand, the ecological protection and repair of the ocean shoreline are completed; the repair composition includes grass seeds and sandy soil;

[0102] Among them, the plant species of the grass seeds include Suaeda salsa and Tamarix chinensis, and the mass ratio of the two is 1:1; the particle size range of the sandy soil is 2000 - 5000 mm; the mass ratio of the grass seeds and the sandy soil is 0.9:1; the distribution density of the grass seeds after dumping is 20 g / m 2 ; the dumping thickness of the repair composition is H, where H ≤ LWL + 0.5 m, and the value range of H is 1.2 m; the duration of the comprehensive action of water and sand is 120 days.

[0103] Example 4

[0104] This example provides a tidal flat repair method based on the reshaping of the microtopography of dredged soil. Except that no anti-seepage layer is set in the submerged dike, the rest are the same as those in Example 1 and will not be elaborated here.

[0105] Example 5

[0106] This embodiment provides a method for intertidal zone restoration based on dredged soil microtopography reconstruction. Except that the dredged soil is dehydrated and then filled, that is, the water content in the dredged soil is 10% (that is, the dredged soil is dried and then filled), the rest is the same as that in Embodiment 1 and will not be elaborated here.

[0107] Embodiment 6

[0108] This embodiment provides a method for intertidal zone restoration based on dredged soil microtopography reconstruction. Except that no algae are added in step (2), the rest is the same as that in Embodiment 1 and will not be elaborated here.

[0109] Embodiment 7

[0110] This embodiment provides a method for intertidal zone restoration based on dredged soil microtopography reconstruction. Except that the filling height of the dredged soil is at a position 0.3 m below the marine datum, the rest is the same as that in Embodiment 1 and will not be elaborated here.

[0111] Embodiment 8

[0112] This embodiment provides a method for intertidal zone restoration based on dredged soil microtopography reconstruction. Except that the filling height of the dredged soil is at a position 0.7 m below the marine datum, the rest is the same as that in Embodiment 1 and will not be elaborated here.

[0113] Embodiment 9

[0114] This embodiment provides a method for intertidal zone restoration based on dredged soil microtopography reconstruction. Except that the filling thickness of the repair composition is H, where H is LWL + 0.6 m, the rest is the same as that in Embodiment 1 and will not be elaborated here.

[0115] Embodiment 10

[0116] This embodiment provides a method for intertidal zone restoration based on dredged soil microtopography reconstruction. Except that the mass ratio of particles with a diameter of less than 20 μm in the dredged soil is 15%, the rest is the same as that in Embodiment 1 and will not be elaborated here.

[0117] Embodiment 11

[0118] This embodiment provides a method for intertidal zone restoration based on dredged soil microtopography reconstruction. Except that the mass ratio of particles with a diameter of less than 20 μm in the dredged soil is 5%, the rest is the same as that in Embodiment 1 and will not be elaborated here.

[0119] Comparative Example 1

[0120] This comparative example provides a method for intertidal zone restoration. The intertidal zone restoration method is the same as that of Example 1 in all aspects except that in step (2), self-balanced dispersion is not carried out. Instead, after the dredged soil and algae are filled in, step (3) is directly carried out, and the restoration is carried out for 390 days. Details are not repeated here.

[0121] Comparative Example 2

[0122] This comparative example provides a method for intertidal zone restoration. The intertidal zone restoration method is the same as that of Example 1 in all aspects except that the restoration composition in step (3) does not include grass seeds. Details are not repeated here.

[0123] Comparative Example 3

[0124] This comparative example provides a method for intertidal zone restoration. The intertidal zone restoration method is the same as that of Example 1 in all aspects except that in step (2), the sandy soil in step (3) is filled in, and in step (3), the dredged soil in step (2) is filled in. Details are not repeated here.

[0125] Comparative Example 4

[0126] This comparative example provides a method for intertidal zone restoration. The intertidal zone restoration method is the same as that of Example 1 in all aspects except that step (3) is carried out first and then step (2). Details are not repeated here.

[0127] Comparative Example 5

[0128] This comparative example provides a method for intertidal zone restoration. The intertidal zone restoration method is the same as that of Example 1 in all aspects except that in step (1), the grass seeds, sandy soil and dredged soil in step (3) are mixed together and filled in step (2), and then the comprehensive restoration is carried out for 390 days (the total restoration days of steps 2 and 3 in Example 1). Details are not repeated here.

[0129] Taking a certain coastal intertidal zone as an example, and taking 200 m of the coastal zone as a test area (with a 100 m interval between each test area), the methods of the above-mentioned examples and comparative examples are used for synchronous experimental research. After nearly 1 year of restoration, the changes in beach elevation, plant biomass and benthic biomass are evaluated, and the evaluation results are shown in Table 1.

[0130] The test results of the above examples and comparative examples are shown in Table 1.

[0131] Table 1

[0132]

[0133]

[0134] It can be seen from Table 1 as follows:

[0135] (1) It can be seen from Comprehensive Examples 1 to 3 that the intertidal zone restoration method based on dredged soil microtopography reshaping provided by the present invention combines the use of submerged dikes, self-balanced dispersion, and comprehensive water and sediment effects, and strictly controls the throwing sequence of dredged soil and restoration composition, and has excellent restoration effects on the intertidal zone. Among them, during the experimental research process, the change in beach elevation is between 70 and 78 cm, and the plant biomass is 370 g / m 2 Above, the biomass of benthic organisms is 197 g / m 2 Above, and the biomass is high after restoration.

[0136] (2) It can be seen from Comprehensive Examples 1 and 4 that in Example 1, it is preferably provided with an impermeable layer at the bottom of the submerged dike. Compared with Example 4 where no impermeable layer is provided, in Example 1, the change in beach elevation is 75 cm, the plant biomass is 386 g / m 2 , and the biomass of benthic organisms is 253 g / m 2 . In Example 4, however, water body penetration and interaction occur inside and outside the submerged dike, the water body environment deteriorates, and the growth of plants and organisms is restricted. Finally, the plant biomass is only 236 g / m 2 , and the biomass of benthic organisms is only 150 g / m 2 . This shows that by preferably providing an impermeable layer at the bottom of the submerged dike, the present invention can further improve the intertidal zone restoration method;

[0137] (3) It can be seen from Comprehensive Examples 1 and 5 that in Example 1, it is preferably to use dredged soil with a water content of 100% without dehydration. Compared with the dredged soil with a water content of only 10% after drying in Example 5, in Example 1, the change in beach elevation is 75 cm, the plant biomass is 386 g / m 2 , and the biomass of benthic organisms is 253 g / m 2 . In Example 5, however, due to the low water content in the dredged soil, not only the original pore structure and the activation performance of the internal organic matter of the dredged soil are damaged during the dehydration process, resulting in a decrease in the biomass of benthic organisms to 225 g / m 2 within the same restoration time, but also the change in beach elevation drops to 68 cm. This shows that the intertidal zone restoration method based on dredged soil microtopography reshaping provided by the present invention preferably uses dredged soil with a higher water content, which can better improve the biomass of benthic organisms after intertidal zone restoration and the intertidal zone restoration effect;

[0138] (4) It can be seen from Comprehensive Examples 1 and 6 that in Example 1, it is preferably to add algae while throwing dredged soil. Compared with Example 6 where no algae are added, in Example 1, the change in beach elevation is 75 cm, the plant biomass is 386 g / m 2 , and the biomass of benthic organisms is 253 g / m 2, while in Example 6, the adsorption effect of algae on organic matter and heavy metals in seawater is lacking, it is difficult to achieve the synergistic effect between algae and dredged soil, and it does not have the effect of providing food for benthic organisms through photosynthesis of algae in Example 1, resulting in the biomass of benthic organisms being only 167 g / m within the same repair time 2 ; This shows that the present invention preferably uses algae and dredged soil in combination, which has a better intertidal zone repair effect, and the biomass of benthic organisms and plants after repair is higher;

[0139] (5) From a comprehensive view of Example 1 and Examples 7 - 8, it can be seen that in Example 1, it is preferably at a position where the filling height of the dredged soil is 0.5 m below the marine datum. Compared with Examples 7 - 8 at positions of 0.3 m and 0.7 m respectively, the changes in beach elevation, plant biomass, and benthic organism biomass in Example 1 are all significantly higher than those in Examples 7 - 8. This shows that by preferably controlling the filling height of the dredged soil within a reasonable range, the present invention can further improve the intertidal zone repair effect;

[0140] (6) From a comprehensive view of Example 1 and Example 9, it can be seen that in Example 1, the filling thickness of the repair composition is preferably H, where H ≤ LWL + 0.5 m. Compared with Example 9 where H is LWL + 0.6 m, the change in beach elevation in Example 1 is 75 cm, the plant biomass is 386 g / m 2 , and the biomass of benthic organisms is 253 g / m 2 , while in Example 9, the beach elevation is relatively high, the benthic activity area is limited, and the resource quantity is limited; This shows that by preferably controlling the filling thickness of the repair composition within a reasonable range, the present invention has a better intertidal zone repair effect, and the benthic organisms after repair are higher;

[0141] (7) From a comprehensive view of Example 1 and Examples 10 - 11, it can be seen that in Example 1, the particle size distribution of the dredged soil is strictly controlled within a reasonable range. Compared with Examples 10 - 11 where the mass ratio of fine particles is respectively too large and too small, the changes in beach elevation, plant biomass, and benthic organism biomass in Example 1 are all significantly higher than those in Examples 10 - 11. This shows that by preferably controlling the particle size distribution of the dredged soil within a reasonable range, the present invention can significantly improve the intertidal zone repair effect;

[0142] (8) It can be seen from the comprehensive Examples 1 and Comparative Examples 1-5 that in Comparative Example 1, after the dredged soil and algae were filled and dumped, step (3) was directly carried out, and the restoration was directly carried out for 390 days. After the restoration, the beach was relatively undulating, with some areas being high and some areas being low, and the restoration effects of the plant biomass and benthic biomass were poor; in Comparative Example 2, the restoration composition did not include grass seeds, lacking the synergistic effect of plants. Not only was the beach elevation small, but also the plant biomass and benthic biomass were significantly lower than those in Example 1; in Comparative Example 3, sandy soil was filled and dumped first, and then dredged soil was filled and dumped. The upper sandy soil was severely eroded, and the restoration effect was significantly reduced. In Comparative Example 4, the grass seeds were buried in the bottom layer, and the plant restoration effect was poor. Moreover, within the same restoration time, the benthic biomass decreased significantly. In Comparative Example 5, all were mixed for restoration, and the comprehensive restoration effect was significantly reduced. Thus, it is shown that the present invention comprehensively fills and dumps the composition of dredged soil and algae, and performs self-balanced dispersion, then fills and dumps the restoration composition containing grass seeds, and performs the comprehensive action of water and sediment, which can achieve good synergistic effects among various steps and substances and improve the restoration effect.

[0143] The present invention uses the above-mentioned examples to illustrate the detailed features of the present invention, but the present invention is not limited to the above-mentioned detailed features, that is, it does not mean that the present invention must rely on the above-mentioned detailed features to be implemented. Those skilled in the art should understand that any improvement to the present invention, the equivalent replacement of the technical features selected by the present invention, the addition of auxiliary technical features, and the selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for intertidal zone restoration based on dredged soil micro-topography reshaping, characterized in that, The intertidal zone restoration method includes the following steps: (1) Construct a submerged breakwater in the offshore intertidal zone; (2) Uniformly dump the dredged soil on the nearshore beach. Under the action of ocean hydrodynamic force and tides, the dredged soil is self-balanced and dispersed between the nearshore and the submerged breakwater; (3) Dump a restoration composition on the nearshore beach. Through the comprehensive action of water and sediment, the ecological protection and restoration of the ocean shoreline are completed; the restoration composition includes grass seeds and sandy soil.

2. The intertidal zone restoration method according to claim 1, wherein, In step (1), the submerged breakwater successively includes an anti-seepage layer and a breakwater body layer from bottom to top; Preferably, the permeability of the anti-permeation layer ≤ 1.0×10 -13 cm / s; Preferably, the material of the anti-seepage layer includes any one or a combination of at least two of anti-seepage concrete, geotextile, steel plate, cement grouting material or gravel layer; Preferably, the material of the breakwater body layer includes gravel; Preferably, the permeability of the embankment body layer is 1×10 -7 cm / s to 1×10 -10 cm / s.

3. The intertidal zone restoration method according to claim 1 or 2, characterized in that The construction position of the submerged breakwater is between 200 m from the shoreline and 500 m from the shoreline; Preferably, the height of the submerged breakwater is between LWL and HWL, where LWL is the lowest tide level and HWL is the highest tide level.

4. The intertidal zone restoration method according to claim 2, wherein The height of the anti-seepage layer in the submerged breakwater is 0.1% - 1% of the total height of the submerged breakwater.

5. The intertidal zone restoration method according to any one of claims 1 to 4, characterized in that In step (2), the water content of the dredged soil is 50% - 150%; Preferably, the material of the dredged soil includes quartz; Preferably, the dredged soil also includes clay; Preferably, the dredged soil also contains organic matter; Preferably, the content of organic matter in the dredged soil is 4.0 - 4.5 g / kg; Preferably, the organic matter in the dredged soil includes any one or a combination of at least two of aquatic plant residues, animal remains, microbial decomposition products or humus; 6. The intertidal zone restoration method according to any one of claims 1 to 5, characterized in that, The particle size range of the dredged soil is below 200 μm; Preferably, the mass ratio of the particle size below 20 μm in the dredged soil is 9% - 12%; Preferably, the mass ratio of the particle size above 75 μm in the dredged soil is 25% - 35%; 7. The intertidal zone restoration method according to any one of claims 1 to 6, characterized in that The dumping height of the dredged soil is at a position 0.4 - 0.6 m below the ocean datum level; Preferably, the dredged soil is dumped at ebb tide; Preferably, the time for self-balanced dispersion is 90 - 365 days.

8. The intertidal zone restoration method according to any one of claims 1 to 7, characterized in that When dumping in step (2), algae are also mixed into the dredged soil; Preferably, the algae include any one or a combination of at least two of Gracilaria lemaneiformis, Undaria pinnatifida, green algae, red algae or brown algae; Preferably, the addition amount of the algae is 0.01% - 0.1 wt% of the dredged soil; 9. The intertidal zone restoration method according to any one of claims 1 to 8, characterized in that, In step (3), the plant species of the grass seeds include any one or a combination of at least two of Suaeda glauca, Spartina anglica, Spartina alterniflora, Tamarix chinensis or Vitex rotundifolia; Preferably, the particle size range of the sandy soil is 150 - 5000 mm; Preferably, the mass ratio of the grass seeds to the sandy soil is 0.8 - 1:1; 10. The intertidal zone restoration method according to any one of claims 1 to 9, characterized in that, The distribution density of the grass seeds after throwing and filling described in step (3) is 20-30 g / m 2 ; Preferably, the dumping thickness of the restoration composition is H, where H ≤ LWL + 0.5 m, and the value range of H is 0.8 - 1.2 m; Preferably, the duration of the comprehensive action of water and sediment is 90 days - 365 days.

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