Method for constructing ecological buffer zone of reservoir hydro-fluctuation zone in southwest karst region

Abstract

The invention provides a construction method of an ecological buffer zone of a reservoir hydro-fluctuation belt in a southwest karst region. The construction method comprises the following steps: S1, dividing a suitable recovery area of the hydro-fluctuation belt; s2, slope reconstruction and substrate improvement; s3, plant variety selection and configuration; s4, planting and maintaining the plants. The original soil condition of the hydro-fluctuation belt is improved through substrate improvement, the tolerance of plants to water level fluctuation is ensured through differentiated seed selection of the regions I-IV, the survival rate of vegetation in karst barren soil is increased, and the restoring capacity of an ecological system of the hydro-fluctuation belt is enhanced. According to the method, the storage submerged plant buffer pond is transformed on the lower portion of the hydro-fluctuation belt area or the artificial aquatic plants are arranged, the ecological buffer space of the hydro-fluctuation belt is prolonged, the storage pollution purification and retaining capacity is improved, and good application prospects are achieved.

Description

Technical Field

[0001] This invention relates to the field of water environment management and water ecological restoration technology, specifically a method for constructing an ecological buffer zone for the drawdown zone of a reservoir in the karst region of Southwest China. Background Technology

[0002] The drawdown zone of a reservoir is a transitional area formed by water level changes during reservoir operation. This area experiences periodic flooding and receding water levels and is frequently influenced by both aquatic and terrestrial ecosystems, possessing important ecological functions such as soil and water conservation, flood regulation, and water purification. However, with long-term reservoir impoundment and non-seasonal discharges, the productivity of the drawdown zone ecosystem gradually declines. Periodic water level fluctuations and alternating wet and dry periods exacerbate the vulnerability of the ecosystem in this region, leading to the gradual loss of its ecological functions.

[0003] In southwestern my country, due to the complex terrain and scarce arable land resources, residents often cultivate land up to the boundary of reservoir drawdown zones. In these areas with frequent human activity, especially grazing, farming, water extraction, and washing, the natural vegetation of the drawdown zones has been damaged to some extent, causing severe degradation of the ecosystem. Furthermore, during rainfall, non-point source pollution from farmland in mountainous areas flows into the drawdown zones via rainwater runoff and eventually into the reservoirs, posing a significant risk to reservoir water quality.

[0004] The drawdown zone is not only the last line of defense for reservoir water quality protection, but also plays a crucial role in preventing soil erosion and reducing pollutants entering the water. However, due to the widespread distribution of karst landforms in Southwest China, the drawdown zone in this region faces more complex ecological restoration challenges. The soils in karst areas are typically infertile, have poor cover, and high pH levels. Furthermore, variations in topography and hydrological conditions pose significant challenges to vegetation restoration in the drawdown zone. In particular, the interaction between alternating wet and dry periods and complex topography, coupled with the karst landforms, limits vegetation restoration and reconstruction.

[0005] Currently, there have been some studies and practices regarding vegetation restoration in drawdown zones, such as the vegetation construction method for the drawdown zone of the Three Gorges Reservoir proposed in patent CN101790933B, and the method using Bermuda grass to restore the drawdown zone in CN105052457B. These methods mainly focus on different types of vegetation configurations and restoration strategies, but most concentrate on conventional ecological restoration of reservoir drawdown zones and do not fully consider the special characteristics of karst landforms in Southwest China. Therefore, in karst regions, the reconstruction and restoration of drawdown zone ecosystems remains a pressing technical challenge. Summary of the Invention

[0006] The purpose of this invention is to provide a method for constructing an ecological buffer zone for the drawdown zone of reservoirs in the karst region of Southwest China, in order to solve the problems in the prior art.

[0007] To achieve the above objectives, the present invention provides the following technical solution: The present invention provides a method for constructing an ecological buffer zone for the drawdown zone of a reservoir in the karst region of Southwest China, comprising the following steps:

[0008] Includes the following steps:

[0009] S1. Delineation of suitable recovery zones in the drawdown zone;

[0010] S2, Slope modification and bottom sediment improvement;

[0011] S3. Plant variety selection and configuration;

[0012] S4. Plant cultivation and maintenance.

[0013] Preferably, S1 includes:

[0014] Based on the frequency of flooding in the drawdown zone and the longest duration of flooding, the area is divided into four zones:

[0015] Zone I: Annual flooding frequency ≤ 5%;

[0016] Zone II: 5% < annual inundation frequency ≤ 30% and longest single inundation time ≤ 30 days;

[0017] Zone III: 30% < annual flooding frequency ≤ 80%;

[0018] Zone IV: Annual inundation frequency > 80% or perennial inundation, and maximum inundation depth ≤ 6m below the highest water level.

[0019] Preferably, S2 includes:

[0020] S201: During the low water level period in spring, clean up surface debris in the drawdown zone and loosen compacted soil;

[0021] If the slope of Zones I-III is greater than 25°, wooden piles, eco-bag low walls, or gabion retaining walls should be installed in Zones II or III.

[0022] If the slope of Zone IV is less than 25°, a buffer pond for entering the reservoir shall be excavated in a flat area of ​​the drawdown zone. The bottom elevation of the pond shall be 1.5-3m lower than the daily operating water level of the reservoir and no more than 6m lower than the maximum water level. The slope ratio shall be 1:1.5 to 1:2.

[0023] S202: The substrate improvement formula is as follows: 100 parts by weight of cleaned backfill soil, 3-5 parts of biochar, 0.5 parts of potassium humate, 0.5 parts of sodium alginate, 0.3-0.5 parts of EM bacteria, and 0.5-1 parts of polyacrylamide.

[0024] Preferably, S3 includes configuring plants by zone:

[0025] Zone I: Planting wetland trees (Mexican bald cypress, Metasequoia glyptostroboides, Populus tomentosa, Populus nigra), wetland shrubs (Symplocos chinensis, Salix babylonica, Salix matsudana), and tall plants (Eucalyptus clavatum, Miscanthus sinensis);

[0026] Zone II: Plant wetland shrubs and herbs (berberis, bullwhip, barnyard grass, coix seed, cyperus rhizome);

[0027] Zone III: Plant flood-tolerant herbs (Bermudagrass, oxtail grass, wild grass, wild clover);

[0028] Zone IV: Submerged plants (such as foxtail algae and pondweed) are planted in the buffer pond where the slope is gentle; artificial bionic aquatic plants are planted in the steep slope.

[0029] Preferably, the artificial bionic aquatic plant is a single-piece ecological substrate (1m × 1.5m), with a counterweight connected to the bottom, and a planting density of 1 piece / m². 2 The direction is perpendicular to the shoreline.

[0030] Preferably, S4 includes:

[0031] Trees and shrubs are planted in holes.

[0032] Bermuda grass was planted in 30×30cm turf.

[0033] Other herbs are propagated by planting or by seed.

[0034] Submerged plants are placed using the method of wrapping soil around their roots and throwing them in.

[0035] Preferably, additional prickly pear and rosehips are planted at the boundary of Zone I near the village to form an isolation zone.

[0036] Preferably, the ecological bag wall is a trapezoidal structure (top width 50cm / bottom width 70cm / height 50cm), and the cross-sectional dimensions of the gabion retaining wall are 1m×1m.

[0037] This invention has at least the following beneficial effects:

[0038] This invention provides a method for constructing an ecological buffer zone in the drawdown zone of a reservoir in the karst region of Southwest China. This method utilizes a substrate improvement formula (biochar + potassium humate + sodium alginate + EM bacteria + polyacrylamide). Biochar improves soil aeration and aggregate structure, alleviating compaction; potassium humate and sodium alginate regulate the pH of high-pH karst soils and enhance fertility; polyacrylamide strengthens soil water retention and aggregation. Differential seed selection in zones I-IV ensures plant tolerance to water level fluctuations, improves vegetation survival rates in karst infertile soils, and enhances the recovery capacity of the drawdown zone ecosystem.

[0039] This invention extends the ecological buffer space of the drawdown zone by modifying the perennially flooded area in the lower part of the drawdown zone into a submerged plant buffer pond or by arranging artificial aquatic plants, thereby improving the purification and retention capacity for pollution entering the reservoir and showing good application prospects. Attached Figure Description

[0040] Figure 1 The method flowchart provided by the present invention.

[0041] Figure 2 This is a schematic diagram illustrating the division of the suitable recovery zone in the drawdown zone according to this embodiment of the invention.

[0042] Figure 3 A schematic diagram of the layout of the ecological buffer zone in the drawdown zone of the reservoir provided by the present invention.

[0043] Figure 4 This is a schematic cross-sectional view of the ecological buffer zone construction provided by the present invention.

[0044] The legend is as follows:

[0045] 1-Ecological buffer zone I; 2-Ecological buffer zone II; 3-Ecological buffer zone III; 4-Ecological buffer zone IV - Submerged plant buffer pond; 5-Ecological buffer zone IV - Artificial bionic aquatic plants; 6-Reservoir area; 7-Village; 8-Ecological bag low wall; 9-Gabion retaining wall; 10-Isolation zone. Detailed Implementation

[0046] Unless otherwise defined, all technical and scientific terms used in this specification have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. The term "and / or" as used in this specification includes any and all combinations of one or more of the associated listed items.

[0047] Example

[0048] Figure 1 This is a flowchart illustrating a method provided in an embodiment of the present invention. In this embodiment, as... Figure 1 As shown, a method for constructing an ecological buffer zone for the drawdown zone of a reservoir in the karst region of Southwest China may include the following steps:

[0049] S1. Delineation of suitable recovery zones in the drawdown zone;

[0050] A field survey of the reservoir's drawdown zone was conducted, and it was divided into four zones based on the frequency of inundation and the longest duration of inundation: Zone I: annual inundation frequency ≤ 5%; Zone II: 5% < annual inundation frequency ≤ 30% and longest single inundation time ≤ 30 days; Zone III: 30% < annual inundation frequency ≤ 80%; Zone IV: annual inundation frequency > 80% or perennial inundation, and maximum inundation depth ≤ 6m below the highest water level. This division allows for the selection of appropriate vegetation and restoration strategies based on the specific conditions of different zones.

[0051] Table 1. Statistics on the average inundation elevation and number of days of the drawdown zone of a certain reservoir in the past five years.

[0052] Submerged elevation Number of days submerged Flooding frequency Longest flooding duration ≥XX71 0 0 0 XX70-XX71 3 0.82％ 3 XX69-XX70 11 3.01％ 5 XX68-XX69 77 21.1％ 15 XX67-XX68 130 35.6％ 22 XX66-XX67 281 76.9％ 148 XX65-XX66 341 93.4％ 283 ≤XX65 365 100％ 365

[0053] The reservoir's management boundary elevation is XX71m, the maximum water level is XX70.1m, and the daily water level in the reservoir area mainly fluctuates between XX66.8m and XX68m.

[0054] Specifically, referring to the data in Table 1, the drawdown zone is divided into four areas based on elevation:

[0055] Zone I (XX69-XX71): Basically unaffected by flooding, with an annual flooding frequency of ≤5%;

[0056] Zone II (XX68-XX69): The overall inundation time is relatively short, with 5% < annual inundation frequency ≤ 30%, and the longest single inundation time ≤ 30 days;

[0057] Zone III (XX66-XX68): The inundation time is relatively long, with an annual inundation frequency of 30% < 80%;

[0058] Zone IV (XX64.1-XX66): Annual inundation frequency > 80% or perennial inundation, and maximum inundation depth ≤ 6m below the highest water level.

[0059] S2, Slope modification and bottom sediment improvement;

[0060] During the low water level period in spring, clear surface debris from the drawdown zone and loosen compacted soil.

[0061] For areas with a slope greater than 25° in zones I-III, wooden piles, eco-bag low walls, or gabion retaining walls are installed to stabilize the slope. In this embodiment, since the slope of the drawdown zone I-III is relatively steep and prone to soil erosion, eco-bag low walls are installed at an elevation of XX68.5m in zone II. The eco-bag low walls have a trapezoidal structure with a top width of 50cm, a bottom width of 70cm, and a height of 50cm. The eco-bags are 40cm×60cm in size and filled with plain soil. Gabion retaining walls are installed at an elevation of XX67m in zone III. The cross-sectional dimensions of the gabion retaining walls are 1m×1m and filled with crushed stone with a particle size of 10-15cm.

[0062] For areas within Zone IV with a slope less than 25°, a buffer pond will be excavated and constructed to a depth of 1m. The excavated sediment will be used to fill the slope, with the slope crest elevation at XX66.5m, a height of 1.5m, and a slope ratio of 1:1.5. After construction, the bottom elevation of the buffer pond will be XX65m. Under normal reservoir operating conditions (XX66.8-XX68m), the water depth of the buffer pond will be 1.8-3m, reaching a depth of 5.6m at the maximum water level (XX70.1m). By constructing the buffer pond, Zone IV can maintain long-term water storage even at low water levels and provide a suitable water depth for the growth of submerged plants.

[0063] After the slope topography is modified, the subgrade is improved. The subgrade improvement formula is as follows: 100 parts by weight of cleaned backfill soil, 3-5 parts of biochar, 0.5 parts of potassium humate, 0.5 parts of sodium alginate, 0.3-0.5 parts of EM bacteria, and 0.5-1 parts of polyacrylamide.

[0064] Biochar can improve the aeration and aggregate structure of soil in the drawdown zone after water recedes, and reduce soil compaction. Adding potassium humate and sodium alginate can not only increase soil fertility, but also regulate the pH of native high-pH soils in karst areas. Materials such as polyacrylamide can improve the soil's water retention capacity and cohesion.

[0065] S3. Plant variety selection and configuration;

[0066] Based on the hydrological conditions and soil characteristics of each region, suitable plant species are selected for planting. Among them, Zone I will be submerged during high water levels, but the submersion time is relatively short. This area is mainly protected by nature, and the plants that can be restored include hygrophilous trees, hygrophilous shrubs, hygrophilous herbs, and tall plants.

[0067] The restored trees are Mexican bald cypress and Metasequoia glyptostroboides, with a diameter at breast height of 6-8 cm and a height of >3 m. The trees are planted at a spacing of no less than 5 m in strips. The shrubs are Chinese bald cypress, southern willow, and autumn willow, with a planting spacing of no less than 1 m. The tall plants are Cassia fistula and Miscanthus sinensis, with a planting density of 25 plants / m2.

[0068] The water level in Zone II fluctuates frequently, and the overall inundation time is relatively short. Wetland shrubs and wetland herbs can be selected. For shrubs, choose Chinese mosquito mother tree, southern willow, and autumn willow. The area between the shrubs should be fully covered with 30cm×30cm Bermuda grass, and the area can be decorated with patches of restored bullwhip, barnyard grass, coix seed, and nutgrass.

[0069] Due to the long overall submersion time in Zone III, the main feature is a perennial flood-tolerant herbaceous community, with 30cm×30cm Bermuda grass turf laid out, and clumps of oxbenefit, wild grass or sedge communities with a diameter of about 1m interspersed.

[0070] Zone IV is submerged for more than 80% of the year. The buffer ponds dug in the gentle slopes are mainly planted with submerged plants such as Myriophyllum spicatum and Potamogeton malaianus, with a species ratio of 1:1 and a planting density of 90 plants / m². 2 Artificial bionic aquatic plants are placed on steep slopes;

[0071] The artificial bionic aquatic plants are installed in single pieces, with the main ecological substrate measuring 1m*1.5m. Holes are drilled in the bottom of the ecological substrate, through which nylon ropes are threaded and connected to the counterweight. The counterweight is a precast concrete block, 1m long and about the same width as the ecological substrate, with a cross-sectional dimension of 10cm*10cm, and internally reinforced with steel bars and hooks.

[0072] The density of artificial bionic aquatic plants is 1 plant (piece) / m² 2 The direction of each piece is perpendicular to the shoreline, that is, perpendicular to the direction of water flow.

[0073] Meanwhile, since the drawdown zone is adjacent to the village, the problem of nearby villagers occupying the drawdown zone area for grazing and farming is quite serious. Therefore, along the boundary of the drawdown zone in Zone I, an additional row of prickly pear and a row of rosehips were planted to form an isolation zone to prevent villagers and livestock from entering the drawdown zone. At the same time, the prickly pear can also generate some economic value.

[0074] S4. Plant cultivation and maintenance;

[0075] Trees and shrubs are planted in holes; Bermuda grass is planted in 30×30cm turf; other herbs are planted by planting or propagating by seed; submerged plants are buried by wrapping the roots with soil and throwing them in.

[0076] Through the above steps, an ecological buffer zone adapted to the characteristics of the drawdown zone of reservoirs in the karst region of Southwest China can be constructed, effectively enhancing the ecological function of the area, strengthening soil and water conservation and water purification capabilities, and protecting local biodiversity.

[0077] This invention extends the ecological buffer space of the drawdown zone by modifying the long-term submerged area into a submerged plant buffer pond or by arranging artificial aquatic plants, thereby improving the purification and retention capacity for pollution entering the reservoir and showing good application prospects.

[0078] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; under the concept of the present invention, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of different aspects of the present invention as described above, which are not provided in detail for the sake of brevity; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for constructing an ecological buffer zone for the drawdown zone of a reservoir in the karst region of Southwest China, characterized in that, Includes the following steps: S1. Delineation of suitable recovery zones in the drawdown zone; S2, Slope modification and bottom sediment improvement; S3. Plant variety selection and configuration; S4. Plant cultivation and maintenance.

2. The method for constructing an ecological buffer zone for the drawdown zone of a reservoir in the karst region of Southwest China according to claim 1, characterized in that, S1 includes: four zones divided according to the frequency of drawdown zone flooding and the longest duration of flooding. Zone I: Annual flooding frequency ≤ 5%; Zone II: 5% < annual inundation frequency ≤ 30% and longest single inundation time ≤ 30 days; Zone III: 30% < annual flooding frequency ≤ 80%; Zone IV: Annual flooding frequency > 80% or perennial flooding.

3. The method for constructing an ecological buffer zone for the drawdown zone of a reservoir in the karst region of Southwest China according to claim 2, characterized in that, S2 includes: S201: During the low water level period in spring, clean up surface debris in the drawdown zone and loosen compacted soil; If the slope of zones I-III is greater than 25°, wooden piles, eco-bag low walls, or gabion retaining walls should be installed in zone II or zone III. If the slope of Zone IV is less than 25°, a buffer pond for entering the reservoir shall be excavated and constructed. The bottom elevation of the pond shall be 1.5-3m lower than the daily operating water level of the reservoir and no more than 6m lower than the maximum water level. The slope ratio shall be 1:1.5 to 1:

2. S202: The substrate improvement formula is as follows: 100 parts by weight of cleaned backfill soil, 3-5 parts of biochar, 0.5 parts of potassium humate, 0.5 parts of sodium alginate, 0.3-0.5 parts of EM bacteria, and 0.5-1 parts of polyacrylamide.

4. The method for constructing an ecological buffer zone for the drawdown zone of a reservoir in the karst region of Southwest China according to claim 3, characterized in that, S3 includes configuring plants by zone: Zone I: Planting wetland trees (Mexican bald cypress, Metasequoia glyptostroboides, Populus tomentosa, Populus nigra), wetland shrubs (Symplocos chinensis, Salix babylonica, Salix matsudana), and tall plants (Eucalyptus clavatum, Miscanthus sinensis); Zone II: Plant wetland shrubs and herbs (berberis, bullwhip, barnyard grass, coix seed, cyperus rhizome); Zone III: Plant flood-tolerant herbs (Bermudagrass, oxtail grass, wild grass, wild clover); Zone IV: Submerged plants (such as foxtail algae and pondweed) are planted in the buffer pond where the slope is gentle; artificial bionic aquatic plants are planted in the steep slope.

5. The method for constructing an ecological buffer zone for the drawdown zone of a reservoir in the karst region of Southwest China according to claim 4, characterized in that, The artificial bionic aquatic plants are single-piece ecological substrates (1m × 1.5m in size), with a counterweight block connected to the bottom, and a planting density of 1 piece / m². 2 The direction is perpendicular to the shoreline.

6. The method for constructing an ecological buffer zone for the drawdown zone of a reservoir in the karst region of Southwest China according to claim 1, characterized in that, S4 includes: Trees and shrubs are planted in holes. Bermuda grass was planted in 30×30cm turf. Other herbs are propagated by planting or by seed. Submerged plants are placed using the method of wrapping soil around their roots and throwing them in.

7. A method for constructing an ecological buffer zone for the drawdown zone of a reservoir in a karst region of Southwest China, as described in claim 2, characterized in that... Additional prickly pear and rosehips were planted along the boundary of Zone I, which is adjacent to the village, to form a buffer zone.

8. A method for constructing an ecological buffer zone for the drawdown zone of a reservoir in a karst region of Southwest China, as described in claim 3, is characterized in that... The eco-bag retaining wall has a trapezoidal structure (top width 50cm / bottom width 70cm / height 50cm), and the cross-sectional dimensions of the gabion retaining wall are 1m×1m.

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