JP4356584B2 - Bedrock groundwater intake facility - Google Patents

Description

  The present invention relates to a bedrock groundwater intake facility, and more particularly, to a bedrock groundwater intake facility using a freshwater lens in which the groundwater made of freshwater has a convex lens shape on an island.

  On islands with a deep non-permeable base, it is known that the groundwater caused by rainfall exists in a lens-like shape floating on seawater or brackish groundwater due to the difference in specific gravity. being called.

In the islands where the highly permeable rocks 1 such as Ryukyu limestone and volcanic rocks are thickly distributed on the hardly permeable rocks 2, the freshwater lens 3 in which the freshwater groundwater has a convex lens shape is often formed in the basement (FIG. 4). reference). In particular, islands made of Ryukyu limestone, which are often found in Okinawa Prefecture, have an extremely high permeability coefficient of about 10 ^-2 to 10 ^-1 cm / sec, so the groundwater level is not high for a lot of rainfall, and the groundwater is a flat freshwater lens. Often exists in the form of The islands made of Ryukyu limestone are often flat and have no rivers, and freshwater lenses are a valuable water resource. However, when developing groundwater such as wells, freshwater lenses may shrink and seawater may enter, and a groundwater development method that can prevent groundwater salinization is desired.

As a typical water resource development method for islands made up of Ryukyu limestone, there are many “water weir” and “salt water intrusion” groundwater dams that are constructed when the hardly permeable rock mass is relatively shallow. When the poorly permeable rock mass is deep as shown in FIG. 4, it is difficult to apply the underground dam technically and costly. In addition, the development of groundwater by a well produces a funnel-shaped water level lowering zone centered on the well, so that the freshwater lens around the well becomes thinner and seawater can easily enter.
Therefore, for the purpose of uniformly collecting groundwater in the freshwater lens from a wide range to reduce the amount of water level drop, as shown in FIG. 5, a vertical shaft 20 reaching the freshwater lens 3 and a freshwater lens from the vertical shaft 20 are shown. 3 has been proposed (see Non-Patent Document 1).
Satoshi Kishi, 4 others, "Groundwater development from freshwater lens using water well in Tsuken Island, Okinawa Prefecture", Applied Geology, Japan Society of Applied Geology, 1998, 39, Vol. 3, p. 298-305

  However, in the bedrock groundwater intake facility described in Non-Patent Document 1, when the amount of pumped water becomes excessive, the freshwater lens 3 may be reduced to 3 ', and seawater s may enter from the bottom surface of the freshwater lens 3. Management of salinization prevention needs to be done on a trial and error basis by changing the amount of pumped water, and practical operation is difficult.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a bedrock groundwater intake facility that can reliably prevent salt watering of a freshwater lens.

In order to achieve the above object, a rock groundwater intake facility according to the present invention is a rock groundwater intake facility that uses a freshwater lens having a convex lens shape as a groundwater composed of freshwater on an island, and is located in the freshwater lens from the ground surface. A shaft with a lower portion as a water absorption tank, a water injection hole that is drilled from the lower portion of the shaft toward the fresh water lens, and feeds water to the fresh water lens, and the fresh water above the water injection hole A water collecting hole is formed in the lens from the shaft toward the fresh water lens, and collects groundwater and feeds it to the water absorption tank.
Here, “a freshwater lens having a convex lens shape” is intended not only for a biconvex lens having the same curvature on the upper and lower surfaces, but also for a freshwater lens having a different curvature on the upper and lower surfaces such as a plano-convex lens.
In the present invention, since the water injection hole is installed below the water collection hole in the fresh water lens, the supplied water is fed from the water injection hole into the fresh water lens, and the fresh water lens is not reduced by pumping. As a result, the intrusion of seawater from the bottom surface of the fresh water lens is prevented, and the fresh water lens is not salted.

  In addition, when using a large-scale freshwater lens as a water source, instead of the above configuration, a rock groundwater intake facility according to the present invention is a shaft that is dug down from the surface to the inside of the freshwater lens, and the lower part is a water absorption tank. A water injection tunnel excavated laterally from the lower part of the shaft, a water injection hole that is drilled from the water injection tunnel toward the fresh water lens, and supplies water to the fresh water lens through the water injection tunnel, A water collection tunnel excavated laterally from the shaft in the fresh water lens above the water injection tunnel and the water injection hole, and drilled from the water collection tunnel toward the fresh water lens to collect groundwater. A water collecting hole for supplying water to the water absorption tank through the water collecting tunnel may be provided.

In the rock groundwater intake facility according to the present invention, a surface water injection hole that is drilled from the ground surface toward the freshwater lens and feeds supply water to the freshwater lens may be provided in the coastal area.
In the present invention, a surface water injection hole drilled from the ground surface toward the fresh water lens is provided in the coastal area, and water is supplied from the surface water injection hole to the periphery of the fresh water lens, so that the seawater from the side of the fresh water lens is Intrusion can be prevented.

  According to the present invention, in addition to the water collecting hole drilled from the vertical surface drilled from the ground surface into the fresh water lens toward the fresh water lens, the hole drilled from the vertical shaft toward the fresh water lens below the water collecting hole. Since the water injection hole is provided, the supply water is fed from the water injection hole into the fresh water lens, and the fresh water lens is not reduced by pumping. As a result, the intrusion of seawater from the bottom surface of the fresh water lens is prevented, and the salt water of the fresh water lens is prevented.

Hereinafter, an embodiment of a bedrock groundwater intake facility according to the present invention will be described based on the drawings.
FIG. 1 is a conceptual diagram showing a first embodiment of a rock groundwater intake facility according to the present invention.
As shown in FIG. 1, the bedrock groundwater intake facility according to the present invention is formed on a low-permeability rock mass 2 such as Shimajiri mudstone, and a high-permeability rock mass 1 such as Ryukyu limestone or volcanic rock surrounded by the sea 4. Constructed on an island consisting of

  The water intake source is a freshwater lens 3 in which groundwater made of freshwater has a convex lens shape, and the freshwater lens 3 is stable in a state where it floats on seawater that has permeated into the highly permeable rock mass 1. In addition, there is a considerable distance from the freshwater lens 3 to the hardly permeable rock mass 2, and it is difficult to construct an underground dam as a water intake facility.

  In this embodiment, the shaft 5 is dug from the ground surface to the bottom of the freshwater lens 3, and the water injection holes 7 drilled from the lower part of the shaft 5 toward the freshwater lens 3 in a substantially horizontal radial direction extend. Further, in the fresh water lens 3, a water collection hole 6 drilled in a substantially horizontal radial direction extends from the shaft 5 toward the fresh water lens 3 above the water injection hole 7.

The lower part of the shaft 5 is a water absorption tank 5 a for storing the groundwater collected by the water collecting hole 6.
In the shaft 5, in order to use the groundwater w stored in the water absorption tank 5a on the ground, there is a pumping pipe 9 arranged from the water absorption tank 5a to the ground and a pumping pump 8 connected to the end of the water pumping pipe 9. Constructed pumping means are provided.

Intake principle of bedrock groundwater intake facility according to the present invention, which utilizes the water head difference between the water level L ₂ and pit water level L ₁ freshwater lens 3, by adjusting the vertical shaft water level L ₁ using a pumping means The amount of water intake can be controlled.
Pit water level L ₁ is the degree somewhat lower than the level L ₂ of the freshwater lens 3, and minimizing the reduction of the fresh water lens 3 by pumping.

However, in the bedrock groundwater intake facility according to the present invention, the water injection hole 7 is provided below the water collection hole 6 in order to further prevent the intrusion of seawater from the bottom surface of the fresh water lens 3 below the vertical shaft 5. To the fresh water lens 3.
The supplied water is sent to the water injection hole 7 via the water injection pipe 12 passing through the packer 7a installed at the base end portion of the water injection hole 7 through the water quality adjusting device 10 and the pressure pump 11 installed on the ground. Water is fed from the water injection hole 7 into the fresh water lens 3.
Thereby, even if the upper water surface of the freshwater lens 3 is somewhat lowered by pumping, the water injection hole 7 becomes a water curtain against seawater intrusion, and saltwater can be reliably prevented. Moreover, since the flow of ground water w from the water injection hole 7 toward the water collection hole 6 is generated by installing the water injection hole 7, the supply water can be considerably recovered and the water intake capacity is further improved.

A part of the groundwater pumped up may be used as the supply water, or sewage treated water, rainwater, or the like may be used, but a water quality adjusting device 10 is installed to prevent clogging during water injection. . The water quality control device 10 is composed of a multi-stage treatment device, and removes large suspensions to very fine suspensions sequentially with a multi-stage treatment device. To do. In addition, when heavy metal ions in the supply water are concerned as a clogging factor, a heavy metal ion treatment device constituted by a heavy metal ion forced oxidation measure and a filtration device is added to the water quality adjusting device 10.
If the supplied water is cleanr than a predetermined standard, the water quality adjustment by the water quality adjusting device 10 is not necessary.

The pressurizing pump 11 is installed as necessary in order to give a water head pressure necessary for preventing the seawater from entering the water injection hole 7. At this time, the required water head (water level) may be about the water level L ₂ of the initial freshwater lens 3.

  In the bedrock groundwater intake facility according to the present embodiment, in addition to the water collecting hole 6 drilled from the shaft 5 into the fresh water lens 3 toward the fresh water lens 3, the shaft 5 is provided below the water collecting hole 6. Since the water injection hole 7 drilled toward the fresh water lens 3 is provided, the supply water is fed into the fresh water lens 3 from the water injection hole 7, and the fresh water lens 3 is not reduced by pumping. As a result, the intrusion of seawater from the bottom surface of the fresh water lens 3 is prevented, and the salt water of the fresh water lens 3 is prevented.

FIG. 2 is a conceptual diagram showing a second embodiment of the rock groundwater intake facility according to the present invention.
As shown in FIG. 2, in the present embodiment, in addition to the first embodiment, the surface water injection hole 13 that is drilled from the ground surface toward the fresh water lens 3 and feeds the supplied water to the fresh water lens 3 is provided in the sea 4. It is installed around the island facing the sea (the coastal area).

Supply water that has passed through the water quality adjusting device 10 and the pressure pump 11 is supplied to the surface water injection hole 13 through the water injection pipe 12.
In the bedrock groundwater intake facility according to the present embodiment, a surface water injection hole 13 drilled from the ground surface toward the fresh water lens 3 is provided in the coastal area, and supply water is supplied from the surface water injection hole 13 to the peripheral portion of the fresh water lens 3. Thus, the intrusion of seawater from the side of the fresh water lens 3 can be prevented.

FIG. 3 is a conceptual diagram showing a third embodiment of the rock groundwater intake facility according to the present invention.
This embodiment is a bedrock groundwater intake facility in the case of using a large-scale freshwater lens 3 as a water source. As shown in FIG. 3, the vertical side of the vertical shaft 5 dug down from the ground surface to the inside of the freshwater lens 3. And a water collection tunnel 14 excavated laterally from the vertical shaft 5 above the water injection tunnel 15 in the fresh water lens 3.

The wall surface of the water collection tunnel 14 is provided with a plurality of water collection holes 16 drilled substantially horizontally toward the fresh water lens 3. The water collection tunnel 14 itself is provided to have a water gradient descending toward the water absorption tank 5a so that the groundwater collected by the water collection hole 16 flows into the water absorption tank 5a.
On the other hand, the wall surface of the water injection tunnel 15 is provided with a plurality of water injection holes 17 that are drilled substantially horizontally toward the fresh water lens 3. The base end portion of the water injection tunnel 15 is sealed by a packer 15a, and the water supplied through the water quality adjusting device 10 and the pressure pump 11 installed on the ground is supplied from the water injection tunnel 15 by the water injection pipe 12 penetrating the packer 15a. The water is supplied to the water injection hole 17 and is supplied from the water injection hole 17 into the fresh water lens 3.

  As mentioned above, although the embodiment of the bedrock groundwater intake facility according to the present invention has been described, the present invention is not limited to the above-described embodiment, and can be appropriately changed without departing from the gist thereof. For example, in the third embodiment, a surface water injection hole may be provided in the coastal area as in the second embodiment. In short, it is only necessary to obtain the desired function in the present invention.

It is a conceptual diagram which shows 1st embodiment of the bedrock groundwater intake facility which concerns on this invention. It is a conceptual diagram which shows 2nd embodiment of the bedrock groundwater intake facility which concerns on this invention. It is a conceptual diagram which shows 3rd embodiment of the bedrock groundwater intake facility which concerns on this invention. It is a conceptual diagram of a freshwater lens. It is a conceptual diagram of the bedrock groundwater intake facility described in the nonpatent literature 1.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Highly permeable rock mass 2 Hardly permeable rock mass 3 Freshwater lens 4 Sea 5, 20 Vertical shaft 5a Water absorption tank 6, 16, 21 Water collecting hole 7, 17 Water injection hole 7a, 15a Packer 8 Pumping pump 9 Pumping pipe 10 Water quality adjustment apparatus 11 Pressurization pump 12 Water injection pipe 13 Surface water injection hole 14 Water collection tunnel 15 Water injection tunnel w Groundwater s Seawater

Claims (3)

A rock groundwater intake facility that uses freshwater lenses in the form of a convex lens.
A shaft that is dug down from the ground surface into the fresh water lens and has a lower portion as a water absorption tank, a water injection hole that is drilled from the lower portion of the shaft toward the fresh water lens, and feeds water to the fresh water lens, and the water injection A rock groundwater intake facility comprising a water collection hole that is drilled from the vertical shaft toward the freshwater lens in the freshwater lens above a hole and collects groundwater and feeds it to the water absorption tank. A rock groundwater intake facility that uses freshwater lenses in the form of a convex lens.
A shaft that is dug down from the ground surface into the fresh water lens and has a lower portion as a water absorption tank, a water injection tunnel that is excavated from the lower portion of the vertical shaft to the side, a hole drilled from the water injection tunnel toward the fresh water lens, and supplied A water injection hole for sending water to the fresh water lens through the water injection tunnel, a water collection tunnel excavated laterally from the shaft in the water injection tunnel and the fresh water lens above the water injection hole, and the water collection A bedrock groundwater intake facility comprising a water collection hole that is drilled from a tunnel toward the fresh water lens and collects groundwater and feeds the water to the water absorption tank through the water collection tunnel.   The rock groundwater intake facility according to claim 1 or 2, further comprising a surface water injection hole formed in a coastal area that is drilled from the ground surface toward the freshwater lens and feeds supply water to the freshwater lens.

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