A method for preventing saltwater intrusion into an aquifer at the bottom of a river channel in an estuary by constructing a barrier

Abstract

The application discloses a method for preventing and treating saltwater intrusion of an aquifer at the bottom of a river estuary channel by building an anti-seepage layer, and comprises the following steps: obtaining hydrogeological data of a prevention and treatment area, determining the size of the area to be prevented and treated according to the expected effect of the project; solidifying the bed of the prevention and treatment area by using a solidifying agent material; performing leveling treatment on the solidified area; laying the anti-seepage layer on the surface of the solidified bed; performing smoothing treatment on the connecting area between the anti-seepage layer and the surrounding bed; and laying a protective layer on the surface of the anti-seepage layer. Compared with the existing method for preventing and treating seawater intrusion, the method has the advantages of relatively simple construction arrangement, small investment cost, low maintenance cost in the later period, and the like, can effectively prevent and treat saltwater intrusion from the bottom of the river channel into the coastal underground aquifer, and has a good application prospect.

Description

Technical Field

[0001] This invention belongs to the field of aquifer seawater intrusion prevention and control, specifically relating to a method for preventing saline water intrusion into the aquifer at the bottom of estuary channels by constructing an impermeable layer. Background Technology

[0002] With the rapid economic development and intensified human activities in coastal and estuarine areas, the demand for water resources has grown rapidly, leading to the over-exploitation of groundwater. Simultaneously, the increasing frequency and intensity of extreme weather events and droughts in recent years have led to a rise in the frequency, intensity, and duration of saltwater intrusion events. This intrusive saltwater seeps into coastal aquifers through riverbeds and banks, causing increased salinity in freshwater, impacting drinking water safety, threatening the quality of irrigation water for farmland, disrupting wetland ecosystem balance, and causing a series of problems such as soil salinization. Existing seawater intrusion prevention technologies primarily target saltwater intrusion into adjacent aquifers from estuaries, riverbanks, or coastal zones; however, there is a lack of measures to prevent saltwater intrusion into aquifers from the bottom of river channels. Summary of the Invention

[0003] Purpose of the invention: In order to overcome the shortcomings of the prior art, the present invention discloses a method for preventing saline water intrusion into the aquifer at the bottom of the estuary by constructing an impermeable layer.

[0004] Technical solution: The method disclosed in this invention for preventing saline water intrusion into the aquifer at the bottom of estuary channels by constructing an impermeable layer includes the following steps: S1. Obtain hydrogeological data of the prevention and control area, and determine the size of the area to be prevented and controlled based on the expected effects of the project; S2. Use curing agent materials to cure the substrate in the prevention and control area; S3. Level the cured area; S4. Lay an impermeable layer on the surface of the solidified substrate; S5. Smooth the connection area between the impermeable layer and the surrounding foundation bed. S6. Lay a protective layer on the surface of the impermeable layer.

[0005] Among them, the hydrogeological data in S1 include aquifer permeability and porosity, average river level, upstream distance of saltwater intrusion, location of the toe of the saltwater wedge of seawater intrusion, geological and geomorphological features of the riverbed, and sediment types at the bottom of the riverbed.

[0006] Furthermore, in S2, the solidifying agent material is selected based on the type of sediment at the bottom of the riverbed in the prevention and control area.

[0007] Furthermore, in S2, appropriate solidification treatment construction technology is selected based on the geological and geomorphological characteristics of the riverbed and the type of sediment at the bottom of the riverbed.

[0008] Furthermore, the materials for the impermeable layer in S4 can be geomembrane, bentonite waterproofing blanket, or underwater concrete.

[0009] Furthermore, in S5, the impermeable layer is extended obliquely into the interior of the surrounding base bed, and then horizontally extended a certain distance within the base bed.

[0010] Furthermore, the protective layer in S6 is an underwater concrete or fluidized solidified soil protective layer.

[0011] Furthermore, in S6, the protective layer covers an area slightly larger than the impermeable layer. The edges of the protective layer are gently sloping with a slope ratio of 1:10-15. The front corners of the gentle slope naturally overlap with the subgrade surface at a small angle.

[0012] Beneficial effects: Compared with existing methods for preventing seawater intrusion, the method proposed in this invention has a relatively simple construction layout, low investment cost, and low maintenance cost. It can effectively prevent saltwater from intruding into coastal underground aquifers from the bottom of river channels and has a good application prospect. Attached Figure Description

[0013] Figure 1 This is a flowchart illustrating the construction process of this invention. Figure 2 This is a schematic diagram of the seepage-proof layer structure of the present invention; Figure 3 A comparison diagram showing the prevention and control effects before and after the construction of the seepage barrier. Detailed Implementation

[0014] The technical solution of the present invention will be further described below with reference to the accompanying drawings. like Figure 1 and Figure 2 As shown, the present invention provides a method for preventing saline water intrusion into the aquifer at the bottom of a river estuary by constructing an impermeable layer, comprising the following steps: (1) Obtain hydrogeological data of the prevention and control area, including aquifer permeability and porosity, average river level, upstream distance of saltwater intrusion, location of the toe of the saltwater wedge of seawater intrusion, geological and geomorphological characteristics of the riverbed, and sediment types at the bottom of the riverbed, and determine the size of the area to be prevented and controlled based on the expected effect of the project.

[0015] (2) Based on the sediment type of the riverbed in the prevention and control area 2, select appropriate solidification materials, such as silt solidification agent for silty riverbed and mud solidification agent for sandy riverbed, etc., to solidify the sediment of a certain thickness on the surface of the riverbed in the prevention and control area 2; based on the geological and geomorphological characteristics of the riverbed and the sediment type, select appropriate solidification treatment construction technology, such as the selection of agitator, and the determination of agitator speed, lifting speed, and agitation power.

[0016] (3) Level the solidified base bed in the prevention and control area 2 to reduce stress concentration caused by local settlement and uneven support, which could damage the seepage prevention layer 3 and lead to the failure of the seepage prevention function.

[0017] (4) Lay an impermeable layer 3 on the solidified subgrade surface to prevent saline water from invading the lower aquifer of the riverbed and thus polluting the coastal groundwater. The impermeable layer 3 material can be geomembrane, bentonite waterproof blanket, underwater concrete, etc., depending on the actual project conditions.

[0018] (5) Transition treatment is carried out on the connection area between the seepage barrier layer 3 and the surrounding foundation bed. Specifically, the seepage barrier layer 3 is extended obliquely into the interior of the surrounding foundation bed 1, and then horizontally extended a certain distance inside the foundation bed 1. The purpose of this treatment is to prevent the boundary area of ​​the seepage barrier layer 3 from being directly eroded and damaged by the river flow, thereby destroying the entire seepage barrier layer 3 and affecting the service life of the project.

[0019] (6) An underwater concrete or fluidized solidified soil protective layer 4 is laid on the surface of the impermeable layer 3 to increase the weight of the impermeable layer 3, reduce the scouring effect of the river flow, and increase its service life. The coverage area of ​​the protective layer 4 should be slightly larger than that of the impermeable layer 3. The edges of the protective layer 4 should be formed into a large gentle slope with a slope ratio of 1:10 to 1:15. The front corner of the gentle slope should naturally overlap with the surface of the subgrade 1 at a small angle, with no boundary scouring points, so as to reduce the generation of turbulence.

[0020] like Figure 3 As shown, the implementation example of the two-dimensional numerical model is as follows: Based on hydrogeological data of the coastal estuary area of ​​Jiangsu Province, a method for preventing saline water intrusion into the aquifer at the bottom of the estuary by constructing an impermeable layer, as provided in this invention, was used. A two-dimensional numerical model was established using COMSOL Multiphysics software to verify the effectiveness of the method.

[0021] In COMSOL Multiphysics software, the two-dimensional numerical model in this embodiment was established using the "Free and Porous Media Flow, Brinkman" interface and the "Rare Material Transport in Porous Media" interface.

[0022] The simulated prevention and control area includes the river channel, the impermeable layer, and the shallow aquifer adjacent to the riverbed, which are simplified into three rectangular areas. The model is 200 m long and 20 m high. The upper layer is the river water body with a thickness of 5 m; the middle layer is the impermeable layer with a thickness of 1 m; and the lower layer is the bedrock (i.e., the shallow aquifer at the bottom of the river) with a thickness of 14 m.

[0023] The upstream boundary is a constant-water-level, constant-concentration freshwater boundary, with a boundary water level of 20 m and a concentration of 0 mol / m³. 3Downstream is the boundary of tidal level isostatic seawater, with a boundary concentration of 600 mol / m³. 3 The average sea level is 18.5 m, the tidal range is 2 m, and the tidal cycle is 1 h; the bottom boundary of the aquifer is set as a non-flow boundary.

[0024] Both the impermeable layer and the aquifer are assumed to be homogeneous and isotropic, and the permeability of the impermeable layer is 1×10⁻⁶. -19 m 2 The porosity was set to 0.01; the permeability of the aquifer was 1×10⁻⁶. -10 m 2 The porosity is 0.4; the density of fresh water is 1000 kg / m³. 3 Seawater density is 1025 kg / m³ 3 The longitudinal and transverse dispersion coefficients of the impermeable layer and the aquifer are 0.1 and 0.01, respectively.

[0025] The model without an impermeable layer was used as a control condition for simulation, and the simulation time was 400 h.

[0026] The simulation results are shown in Figure 3. Compared with the case without an impermeable layer, in the case with the impermeable layer, the total length of the saltwater wedge in the aquifer was reduced by 56.8%, the degree of saltwater intrusion in adjacent aquifers at the bottom of the river channel in the area reached by the upstream salt tide was reduced, and the area of ​​saltwater intrusion with salinity above 0.45‰ in shallow aquifers was reduced by 31.6%. The comparative results show that laying an impermeable layer at the bottom of the river channel according to the method provided by this invention can significantly reduce the degree of saltwater intrusion in shallow aquifers and force the saltwater wedge at the bottom of the shallow aquifer to retreat towards the sea. Although the numerical model is highly simplified, the above simulation results show that the method provided by this invention for preventing saltwater intrusion in aquifers at the bottom of estuary channels by constructing an impermeable layer is effective.

Claims

1. A method for preventing saline water intrusion into the aquifer at the bottom of a river estuary by constructing an impermeable layer, characterized in that, Includes the following steps: S1. Obtain hydrogeological data of the prevention and control area, and determine the size of the area to be prevented and controlled based on the expected effects of the project; S2. Use curing agent materials to cure the substrate in the prevention and control area; S3. Level the cured area; S4. Lay an impermeable layer on the surface of the solidified substrate; S5. Smooth the connection area between the impermeable layer and the surrounding foundation bed. S6. Lay a protective layer on the surface of the impermeable layer; S1 contains hydrogeological data including aquifer permeability and porosity, average river level, upstream distance of saltwater intrusion, location of the toe of the saltwater wedge, geological and geomorphological features of the riverbed, and sediment types at the bottom of the riverbed. S2 selects solidifying agent materials based on the sediment types at the bottom of the riverbed in the prevention and control area. S2 also selects appropriate solidification treatment construction techniques based on the geological and geomorphological features of the riverbed and the sediment types at the bottom of the riverbed. S4 selects geomembranes, bentonite waterproofing blankets, or underwater concrete as the materials for the impermeable layer. S5 specifically involves extending the impermeable layer obliquely into the surrounding subgrade and horizontally extending it a certain distance within the subgrade. S6 uses underwater concrete or fluidized solidified soil as the protective layer. The protective layer covers an area slightly larger than the impermeable layer, with gentle slopes at the edges, a slope ratio of 1:10-15, and a small-angle natural overlap between the front corner of the slope and the subgrade surface.

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