Rain garden and construction method for the same

Abstract

To provide a rain garden that can be easily constructed, is easy to maintain, and harmonizes with the surrounding natural environment, and a construction method for the same.SOLUTION: A rain garden of the present invention comprises a recess 11 formed in the soil, comprising a bottom surface 12 and side surfaces 13, and a rainwater introduction part 16 that introduces rainwater from the surroundings of the recess 11 into an interior 11a of the recess 11. The bottom surface 12 of the recess 11 includes a permeable structure 14 formed by directly laying organic material on a soil 18 of the bottom surface 12.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a rain garden and a construction method thereof. [Background technology]

[0002] In recent years, rain gardens have been attracting attention as a form of green infrastructure. A rain garden is a planted space designed to temporarily store rainwater that falls on the ground and allow it to slowly seep into the ground, rather than directly discharging it into storm drains. For example, rain gardens are known that are constructed beside roads or pavements by covering an excavated area with gravel so as to blend in with the surrounding structures, and direct rainwater into the gravel so that it infiltrates into the ground. Furthermore, Patent Document 1 discloses a rain garden in which a recess formed by excavation is backfilled with soil for growing plants via a planar water shield, in which the planar water shield has a structure that allows plant roots to penetrate and is composed of a number of water shield sheets, each of which covers a predetermined area within the recess, and in which water-permeable gaps are formed between adjacent water shield sheets or at the joints between adjacent water shield sheets. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2023-2136 A Summary of the Invention [Problem to be solved by the invention]

[0004] The above-mentioned conventional rain gardens with gravel require construction costs such as transportation costs for the gravel, etc. Also, when fallen leaves from roadside trees and garbage fly onto the gravel and get into the gaps in the gravel, they clog the gaps and reduce permeability, they attract weeds, and they look undesirable, so they require regular cleaning and replacement of the gravel every few years, which causes problems with maintenance and management. Furthermore, the rain garden described in Patent Document 1 requires a process of laying a planar water shield over the entire recess and backfilling the excavated soil, which is a large-scale operation. The present invention has been made in consideration of the above circumstances, and has an object to provide a rain garden and its construction method that is easy to construct, maintain, and blend in with the surrounding natural environment. [Means for solving the problem]

[0005] The inventors discovered that by constructing a rain garden in an existing green space such as a forest or park, it can blend in with the green space, and utilize the inherent rainwater infiltration capacity of the green space, providing sufficient functionality as a rain garden. The inventors also discovered that by utilizing the resources within the green space, the rain garden can be easily constructed and maintained, which led to the invention. In other words, the present invention is a rain garden which has a recess formed in the soil, consisting of a bottom and sides, and a rainwater inlet which introduces rainwater from the periphery of the recess into the interior of the recess, the bottom of the recess having a permeable structure formed by laying organic matter directly on the soil at the bottom.

[0006] The organic matter is preferably at least one selected from plants, fallen trees, fallen branches, fallen leaves, felled trees, felled branches, grass clippings, chips, and humus thereof.

[0007] The side surface is preferably a sloped surface.

[0008] It is preferable that the slope is treated with at least one of a topsoil runoff suppression mat, brushwood, lawn, plantings, retaining fences, stone walls, and sandbags.

[0009] The topsoil runoff control mat is preferably biodegradable.

[0010] It is preferable that the water permeability velocity V1 in the soil at the bottom is greater than the water permeability velocity V2 in the soil at the slope.

[0011] The water permeable structure is preferably provided below the lower end of the rainwater introduction section.

[0012] The rain garden construction method of the present invention comprises an excavation step of excavating the soil to form a recess consisting of a bottom and sides, a rainwater inlet installation step of providing a rainwater inlet that guides rainwater from the periphery of the recess into the interior of the recess, and a permeable structure formation step of laying organic matter directly on the bottom to provide a permeable structure.

[0013] In the rain garden construction method of the present invention, the organic matter is preferably one or more selected from plants, fallen trees, fallen branches, fallen leaves, felled trees, felled branches, grass clippings, chips, and humus thereof.

[0014] In the excavation step, it is preferable that the side surface is made into a slope.

[0015] It is preferable to carry out soil retaining treatment on the slope by laying at least one of a topsoil runoff suppression mat, brushwood, lawn, plantings, soil retaining fence, stone wall, and sandbags.

[0016] It is preferable that the method further comprises a step of planting trees on the slope.

[0017] In the water permeable structure forming step, it is preferable to provide the water permeable structure below the lower end of the rainwater introducing portion. Effect of the Invention

[0018] According to the present invention, it is possible to provide a rain garden and a construction method thereof that can be easily constructed, is easy to maintain, and blends in with the surrounding natural environment. [Brief description of the drawings]

[0019] [Figure 1] FIG. 1 is a plan view showing one embodiment of the rain garden of the present invention. [Diagram 2] 2 is a cross-sectional view taken along the line AA in FIG. [Diagram 3] 11A and 11B are cross-sectional views showing other forms of recesses. [Figure 4]FIG. 2 is a cross-sectional view showing one embodiment of the rain garden construction method of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. First, one embodiment of the rain garden will be described with reference to FIGS.

[0021] [Rain garden] The rain garden 10 of this embodiment utilizes existing green spaces such as forests and parks (hereinafter sometimes abbreviated as "green spaces"), and utilizes the soil between the trees. By forming a rain garden within a green space, construction can be simplified and the inherent high rainwater infiltration capacity of the soil in the green space can be utilized. Furthermore, because an existing green space can be utilized, it is possible to achieve harmony and a sense of unity with the surrounding natural environment.

[0022] As shown in Figures 1 and 2, the rain garden 10 of this embodiment has a recess 11 formed in soil 18 and consisting of a bottom 12 and sides 13, and a rainwater inlet 16 that introduces rainwater from the periphery of the recess 11 into the interior 11a of the recess 11, and the bottom 12 of the recess 11 has a permeable structure 14 formed by laying organic matter directly on the soil 18 of the bottom 12. Each component will be described in detail below.

[0023] (recess) The recesses 11 can be obtained by excavating flat or sloping natural soil 18 between trees. There are no particular limitations on the shape of the recesses 11 and various shapes can be adopted, but it is preferable that the recesses 11 have a shape that blends in with the natural environment, such as a circular, elliptical, or irregular shape. The capacity of the recess 11 of the rain garden 10 depends on the maximum rainfall at the construction site, the rainwater infiltration capacity of the soil at the construction site, the area of ​​the construction site, the stratum, etc., and is not particularly limited, but is preferably 2 m 3In order to realize such a water storage capacity, for example, the depth of the inside 11a of the recess 11 is preferably 10 cm to 60 cm, more preferably 20 cm to 50 cm, from the viewpoint of safety. 2 More preferably, it is equal to or greater than this.

[0024] The side surface 13 of the recess 11 may be vertical or may be an inclined slope 13a. In order to create a sense of unity with the surrounding environment and to prevent the runoff of topsoil, the slope 13a is preferable. The angle of the slope 13a is preferably selected according to the topography of the construction site.

[0025] (water permeable structure) The bottom surface 12 of the recess 11 has a water-permeable structure 14 formed by laying organic matter directly on the soil 18 of the bottom surface 12. The water-permeable structure 14 of this embodiment is formed by laying fallen leaves 14a over the entire bottom surface 12, as shown in Figures 1 and 2. The organic matter is not particularly limited as long as it is a natural organic matter, but in consideration of permeability, harmony with nature, workability, etc., it is preferable to use at least one selected from plants, fallen trees, fallen branches, fallen leaves, felled trees, felled branches, grass clippings, chips, and their humus, and more preferably fallen branches and fallen leaves. Humus includes livestock manure, compost, leaf mold, agricultural residues, food residues, and agricultural residues and food residues decomposed by microorganisms, etc. The permeable structure may be a layered structure using two or more of the above organic matter, taking into consideration the permeability of each.

[0026] By using organic matter as described above, the resources within the green space can be effectively utilized, resulting in a design that harmonizes with and is integrated with the green space. Furthermore, when the organic matter comes into direct contact with the soil, it attracts and activates soil organisms such as earthworms and insects. As soil organisms live within the permeable structure 14 and the soil 18 on the bottom surface 12, the soil 18 becomes more aggregated, forming appropriate voids that allow rainwater to infiltrate well. For this reason, the rain garden 10 of this embodiment is able to store and drain rainwater well.

[0027] In addition, the use of organic matter has the advantage of being less labor intensive and less costly than the conventional method of laying gravel or soil, and easier to maintain after construction. In particular, fallen branches and leaves can be collected from trees around the rain garden and laid down, and fallen leaves from autumn to winter can also be used automatically.

[0028] The fallen leaves may be from either coniferous or broad-leaved trees, but from the viewpoint of biodegradability, the leaves of broad-leaved trees are preferred.

[0029] The depth of the water-permeable structure 14 is not particularly limited, but if it is too shallow, the attraction and activation of soil organisms is insufficient, and if it is too deep, the infiltration capacity of rainwater is reduced, so the depth can be set to 5 cm or more and 30 cm or less. In addition, from the viewpoint of preventing clogging of the rainwater introduction part 16, the water-permeable structure 14 is preferably provided below the lower end 16a of the rainwater introduction part 16.

[0030] (Earth retaining treatment) The slope 13a is provided with retaining treatment by laying at least one of a topsoil runoff prevention mat, brushwood, lawn, plantings, retaining fence, stone wall, and sandbags. In this embodiment, as shown in FIG. 1, a retaining treatment 15 is shown in which a topsoil erosion prevention mat 15a and fascines 15b are laid on a slope 13a, but it may be composed of only a topsoil erosion prevention mat 15a or only fascines 15b.

[0031] The topsoil runoff suppression mat 15a provided on the slope 13a may be a mat that mainly serves as a retaining wall, or may have other functions added thereto. Examples include a flying seed receiving mat, a vegetation sheet, a vegetation mat, a vegetation net, and a vegetation sandbag. In particular, by using a flying seed receiving mat, it is possible to capture seeds that have flown onto the slope 13a over time, and it is possible to grow plants. When plants grow on the slope 13a, the strength of the soil increases as the plant roots spread, so that the slope 13a can have a water retention function, and it is possible to suppress the collapse of the slope 13a and the runoff of the topsoil. From the viewpoint of environmental protection, the topsoil runoff suppression mat 15a is preferably biodegradable. Examples of commercially available biodegradable flying seed waiting mats include "Flying Station" (manufactured by Nihon Shokusei Co., Ltd.) and "Crust Mat Deluxe 50" (manufactured by Nikken Kasei Co., Ltd.). Examples of commercially available vegetation sheets include those under the trade name "Kyoujinga ST60 (manufactured by Nippon Shokusei Co., Ltd.)" and those under the trade name "Ecomat (jute net)" (manufactured by Nikken Kasei Co., Ltd.).

[0032] Here, "sodachi" refers to a bundle of tree branches with a diameter of about a few centimeters. From the viewpoint of utilizing green space resources, it is preferable that the brushwood 15b is collected in the vicinity where the rain garden 10 is to be constructed, but brushwood collected in other green spaces may also be used. By using brushwood 15b collected in the vicinity as a retaining wall, it is possible to achieve harmony and a sense of unity with the green space. Brushwood 15b can also provide a habitat for amphibians (toads, etc.), reptiles (snakes, lizards, etc.), insects (long-horned beetles, stag beetles, etc.), and other arthropods (spiders, millipedes, etc.). As shown in FIG. 3, it is preferable to lay brushwood 15b particularly around the opening of the rainwater inlet 16 in order to hide the rainwater inlet 16.

[0033] The topsoil runoff suppression mat 15a and the fascines 15b may be arranged not only on the slope 13a but also on the slope shoulder 13b.

[0034] (Rainwater permeability) The rain garden 10 of this embodiment has a permeable structure 14 made by laying organic matter directly on the soil 18 at the bottom surface 12. This allows soil organisms such as earthworms and insects to live in the soil 18 at the bottom surface 12, promoting soil aggregates and making the soil more permeable than the soil of a traditional green space. The permeability of soil can be measured, for example, by the recovery method, in which water is pumped from a borehole in the soil, and the change in the water level in the borehole as it recovers and returns to equilibrium is measured over time to determine the permeability coefficient. The soil 18 at the bottom 12 of the rain garden 10 of this embodiment has a hydraulic conductivity k of about 3×10 -5 It is possible to achieve a speed of more than m / s.

[0035] At the bottom surface 12 of the recess 11, rain that falls on the bottom surface 12, rainwater that has flowed down the surface of the slope 13a, and rainwater that has flowed from the rainwater introduction section 16 or the surrounding ground surface collect and permeate into the soil 18 at the bottom surface 12. On the other hand, at the slope 13a, rain that falls on the slope 13a and rainwater that flows in from the surrounding ground surface 17 permeate. If there is a significant difference between the water permeation velocity V1 (see FIG. 2) inside the soil of the bottom surface 12 and the water permeation velocity V2 (see FIG. 2) inside the soil of the slope 13a, rainwater can be temporarily stored and then smoothly infiltrated into the soil 18 of the bottom surface 12. It is also preferable that the water permeation velocity V1 inside the soil of the bottom surface 12 is greater than the water permeation velocity V2 inside the soil of the slope 13a.

[0036] (Rainwater inlet section) The rainwater introduction section in the present invention introduces rainwater from the periphery of the recess 11 to the interior 11a of the recess 11. The shape and material of the rainwater introduction section 16 are not particularly limited as long as it introduces rainwater, and examples of such rainwater introduction section 16 include road and pavement gutters, berms, rain gutters, and pipes made of natural materials such as stone and gravel, concrete, resin, etc. In this embodiment, the rainwater introduction section 16 is made of a resin pipe. The rainwater introduction section 16 extends from the rainwater introduction port 20 of the road 21 to the recess 11, protrudes from the slope 13a, and is disposed with its opening facing the interior 11a. The protruding point of the rainwater inlet 16 may be anywhere in the depth direction of the interior 11a of the recess 11, but as mentioned above, in order to prevent clogging of the pipe, it is preferable to install the rainwater inlet 16 so that the permeable structure 14 is located below the lower end 16a of the rainwater inlet 16.

[0037] (Other configurations) The slope 13a may be planted with planting 19. Planting the planting 19 can prevent the slope 13a from collapsing and the topsoil from escaping from the slope 13a. Planting the planting 19 can also hide the topsoil erosion suppression mat 15a over time, which is preferable in terms of appearance. The planting 19 may be planted not only on the slope 13a, but also on the slope shoulder 13b and the surrounding ground surface 17 of the recess 11. The plants used for planting 19 can be native plants that grew naturally in the area excavated when forming recess 11. In this way, it is possible to preserve the natural environment before excavation.

[0038] In this embodiment, an example in which one rain gutter 10 is provided has been given, but a structure in which a plurality of rain gutter 10 are provided adjacent to each other or connected together may also be used.

[0039] Next, one embodiment of the rain garden construction method of the present invention will be described with reference to FIG. [How to construct a rain garden] As shown in Figure 4, the construction method for the rain garden in this embodiment includes an excavation process (Figure 4(a)) of excavating soil 18 to form a recess 11 consisting of a bottom surface 12 and sides 13, a rainwater inlet installation process (Figure 4(b)) of providing a rainwater inlet 16 that introduces rainwater from the periphery of the recess 11 to the interior 11a of the recess 11, a retaining soil treatment process (Figure 4(c)) of providing a retaining soil treatment 15 on the side surface 13 (slope 13a), and a permeable structure formation process (Figure 4(d)) of laying organic matter on the bottom surface 12 to provide a permeable structure 14.

[0040] (Drilling process) First, as shown in FIG. 4(a), soil 18 is excavated between trees or by felling trees to form a recess 11 consisting of a bottom surface 12 and a side surface 13. In this embodiment, the side surface 13 is an inclined slope 13a. From the viewpoint of simple construction, it is not necessary to fell trees. The excavation work in this embodiment can be performed by a known method. Since the depth of the recess 11 is about 60 cm or less as described above, the excavation work may be performed using heavy machinery, but it can also be performed by hand.

[0041] (Rainwater introduction part installation process) The rainwater introduction part installation step is a step of installing a rainwater introduction part 16 that introduces rainwater from the periphery of the recess 11 to the inside 11a of the recess 11, as shown in FIG. 4(b). The rainwater introduction part 16 may be installed at any position in the depth direction of the recess 11. Therefore, depending on the installation position, the rainwater introduction part installation step may be performed before or after the excavation step, or may be performed in parallel with the excavation step. In this embodiment, the rainwater introduction part 16 is installed near the middle of the recess 11 in the depth direction, so it is preferable that the introduction part installation step be performed in parallel with the excavation step. It is preferable that the rainwater introduction portion 16 extends from the rainwater introduction port 20 of the road 21 to the recess 11, protrudes from the slope 13a, and is disposed with its opening facing the interior 11a.

[0042] (Earth retaining treatment process) Next, after the excavation process and the rainwater introduction section installation process, at least one of a topsoil runoff suppression mat, fascine, lawn, planting, retaining fence, stone wall, and sandbag is laid on the slope 13a to perform soil retaining treatment. In this embodiment, as shown in FIG. 4(c), a topsoil runoff suppression mat 15a is laid. The topsoil runoff suppression mat 15a is cut appropriately according to the size of the slope 13a and fixed to the soil with staples or pegs. For example, fascine 15b can be made by appropriately bundling thin branches. It is easier to use branches from the green space around the rain garden 10. The fascine 15b is installed along the slope 13a while driving wooden stakes to prevent it from collapsing. Other soil retaining treatments can be performed by known methods.

[0043] (Water permeable structure formation process) Next, as shown in FIG. 4(d), organic matter is laid directly on the bottom surface 12 to provide a water-permeable structure 14. As described above, the organic matter is preferably one or more selected from plants, fallen trees, fallen branches, fallen leaves, felled trees, felled branches, grass clippings, chips, and humus plants thereof. These can be laid manually. In this way, since the organic matter can be laid manually, there is no need to use large-scale machinery, making it a simple process.

[0044] (Other processes) As described above, planting 19 may be performed on the slope 13a, the slope shoulder 13b, and the surrounding ground surface 17. On the slope 13a, planting 19 can be easily performed by planting plants in appropriate gaps in the soil retaining treatment such as the topsoil runoff suppression mat 15a. In addition, a fence to prevent people from falling may be provided on the ground surface 17 surrounding the rain garden 10.

[0045] The rain garden of the present invention is built in an existing green space, so it is possible to utilize the inherent rainwater infiltration capacity of the soil in the green space. In addition, by effectively utilizing the resources of the green space, such as a permeable structure made of organic matter, it is possible to provide a rain garden that is in harmony with nature and provides a sense of unity. In this way, by utilizing the resources of the green space, it can greatly contribute to the conservation of biodiversity. In addition, by creating a permeable structure by laying organic matter directly on the soil, permeability is maintained by the power of soil organisms, eliminating the need for work such as cleaning and replacing gravel layers as in conventional technology. Furthermore, since the rain garden construction method of the present invention allows for hand-made construction using green space resources, it can be expanded not only to the development of rain gardens in cities, factories, etc., but also to citizen-participation workshops in parks, schools, etc. EXAMPLES

[0046] The present invention will be described in detail below with reference to examples. However, the present invention is not limited to the examples shown below.

[0047] The construction location and configuration of the rain garden in this embodiment are as follows. (1) Construction site: Obayashi Corporation Technical Research Institute (2) Structure of the rain garden Storage capacity: Approx. 2.3 m 3 Permeable structure: Deciduous broadleaf trees Retaining soil treatment: Seed receiving mat (product name "Flying Station", manufactured by Nihon Shokusei Co., Ltd.) and brushwood Depth below rainwater inlet: 30cm Geology: Loamy soil Permeability coefficient k: approx. 3.6 x 10 -5 m / s to 1.4 × 10 -4 m / s

[0048] In loamy soils, which are widely distributed in Japan, the hydraulic conductivity k is usually 1.0×10 -5 Since the permeability is less than about m / s, it can be seen that the permeability of the rain garden of the present invention is higher than that of ordinary soil. [Explanation of symbols]

[0049] 10 Rain garden 11 Recess 11a (inside of recess) 12 Bottom 13 Side 13a Slope 13b Shoulder 14 Water permeable structure 14a Fallen leaves 15 Retaining wall treatment 15a Soil runoff control mat 15b coarse 16 Rainwater introduction section 16a (Lower end of rainwater inlet) 17 Surrounding ground surface 18 Soil 19 Planting 20 Rainwater inlet 21 Road

Claims

1. A recess provided in the soil and having a bottom surface and a side surface; A rainwater introduction portion that introduces rainwater from the periphery of the recess into the inside of the recess, The bottom surface of the recessed portion has a permeable structure formed by laying organic matter directly on the soil at the bottom surface of the rain garden.

2. 2. The rain garden according to claim 1, wherein the organic matter is at least one selected from plants, fallen trees, fallen branches, fallen leaves, felled trees, felled branches, grass clippings, chips, and humus thereof.

3. The rain garden according to claim 1, wherein the side surface is a slope.

4. 4. The rain garden according to claim 3, wherein the slope has been treated to retain soil by laying at least one of a topsoil runoff prevention mat, brushwood, lawn, plantings, retaining fences, stone walls, and sandbags.

5. 5. The rain garden according to claim 4, wherein the topsoil runoff control mat is biodegradable.

6. 4. The rain garden according to claim 3, wherein the permeability velocity V1 in the soil at the bottom is greater than the permeability velocity V2 in the soil at the slope.

7. 2. The rain garden according to claim 1, wherein the permeable structure is provided below the lower end of the rainwater introduction section.

8. An excavation step of excavating soil to form a recess having a bottom surface and a side surface; a rainwater introduction section installation step of providing a rainwater introduction section for introducing rainwater from the periphery of the recess into the inside of the recess; a water permeable structure forming step of laying an organic matter directly on the bottom surface to provide a water permeable structure; A construction method for a rain garden that includes the following features.

9. 9. The method for constructing a rain garden according to claim 8, wherein the organic matter is one or more selected from plants, fallen trees, fallen branches, fallen leaves, felled trees, felled branches, grass clippings, chips, and humus thereof.

10. The method for constructing a rain garden according to claim 8, wherein the side surface is sloped in the excavation step.

11. The method for constructing a rain garden according to claim 10, wherein at least one of a surface soil runoff prevention mat, brushwood, lawn, plantings, retaining fence, stone wall, and sandbags is laid on the slope to perform retaining soil treatment.

12. The method for constructing a rain garden according to claim 11, further comprising a step of planting plants on the sloped surface.

13. The rain garden construction method according to claim 8, wherein in the water permeable structure forming step, the water permeable structure is provided below a lower end of the rainwater introduction portion.

Images