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A rain garden is a planted depression or a hole that allows rainwater runoff from impervious urban areas, like roofs, driveways, walkways, parking lots, and compacted lawn areas, the opportunity to be absorbed. This reduces rain runoff by allowing stormwater to soak into the ground (as opposed to flowing into storm drains and surface waters which causes erosion, water pollution, flooding, and diminished groundwater).〔 University of Rhode Island. Healthy Landscapes Program. (“Rain Gardens: Enhancing your home landscape and protecting water quality.” )〕 They should be designed for specific soils and climates.〔Dussaillant et al. () Journal of Hydrologic Engineering〕 The purpose of a rain garden is to improve water quality in nearby bodies of water and to ensure that rainwater becomes available for plants as groundwater rather than being sent through stormwater drains straight out to sea. Rain gardens can cut down on the amount of pollution reaching creeks and streams by up to 30%. Native and adapted plants are recommended for rain gardens because they are more tolerant of one’s local climate, soil, and water conditions; have deep and variable root systems for enhanced water infiltration and drought tolerance; habitat value and diversity for local ecological communities; and overall sustainability once established. There can be trade-offs associated with using native plants, including lack of availability for some species, late spring emergence, short blooming season, and relatively slow establishment. The plants — a selection of wetland edge vegetation, such as wildflowers, sedges, rushes, ferns, shrubs and small trees — take up excess water flowing into the rain garden. Water filters through soil layers before entering the groundwater system. Root systems enhance infiltration, maintain or even augment soil permeability, provide moisture redistribution, and sustain diverse microbial populations involved in biofiltration.〔B.C. Wolverton, Ph.D., R.C. McDonald-McCaleb (1986). (“Biotransformation of Priority Pollutants Using Biofilms and Vascular Plants.” ) ''Journal Of The Mississippi Academy Of Sciences.'' Vol. XXXI, pp. 79-89.〕 Also, through the process of transpiration, rain garden plants return water vapor to the atmosphere.〔A. Dussaillant, Ph.D., et al. (2005). () ''Water Science & Technology: Water Supply journal.'' Vol. 5, pp. 173-179.〕 A more wide-ranging definition covers all the possible elements that can be used to capture, channel, divert, and make the most of the natural rain and snow that falls on a property. The whole garden can become a rain garden, and each component of the whole can become a small-scale rain garden in itself. ==Restoring the water cycle and mitigating urbanization== In developed areas, natural depressions where storm water would pool, are filled in. The surface of the ground is often leveled or paved. Storm water is directed into storm drains which often may cause overflows of combined sewer systems or poisoning, erosion or flooding of waterways receiving the storm water runoff.〔Kuichling, E. 1889. “The relation between the rainfall and the discharge of sewers in populous districts.” ''Trans. Am. Soc. Civ. Eng.'' 20, 1–60.〕〔Leopold, L. B. 1968. (“Hydrology for urban land planning: A guidebook on the hydrologic effects of urban land use.” ) ''Geological Survey Circular'' 554. United States Geological Survey.〕〔Waananen, A. O. 1969. “Urban effects on water yield” in W. L. Moore and C. W. Morgan (eds), ''Effects of Watershed Changes on Streamflow.'' University of Texas Press, Austin and London.〕 Redirected storm water is often warmer than the groundwater normally feeding a stream, and has been linked to upset in some aquatic ecosystems primarily through the reduction of dissolved oxygen (DO). Storm water runoff is also a source of a wide variety of pollutants washed off hard or compacted surfaces during rain events. These pollutants include volatile organic compounds, pesticides, herbicides, hydrocarbons and trace metals〔Novotny, V. and Olem, H. 1994. “Water Quality: Prevention, Identification, and Management of Diffuse Pollution.” Van Nostrand Reinhold, New York.〕 Rain gardens are designed to capture the initial flow of storm water and reduce the accumulation of toxins flowing directly into natural waterways through ground filtration. They also reduce energy consumption. For example, “the cumulative storage capacity of these rain gardens exceeds a conventional stormwater’s system’s by 10 times.” The National Science Foundation, the United States Environmental Protection Agency, and a number of research institutions are presently studying the impact of augmenting rain gardens with materials capable of capture or chemical reduction of the pollutants to benign compounds. Rain gardens are often located near a building’s roof drainpipe (with or without rainwater tanks). Most rain gardens are designed to be an endpoint of drainage with a capacity to percolate all incoming water through a series of soil or gravel layers beneath the surface plantings. A French drain may be used to direct a portion of the rainwater to an overflow location for heavier rain events. By reducing peak stormwater discharge, rain gardens extend hydraulic lag time and somewhat mimic the natural water cycle displaced by urban development and allow for groundwater recharge. While rain gardens always allow for restored groundwater recharge, and reduced stormwater volumes, they may also increase pollution unless remediation materials are included in the design of the filtration layers . The primary challenge of rain garden design centers on calculating the types of pollutants and the acceptable loads of pollutants the rain garden's filtration system can handle during storm-water events. This challenge is specifically acute when a rain event occurs after a longer dry period. The initial storm water is often highly contaminated with the accumulated pollutants from dry periods. Rain garden designers have previously focused on finding robust native plants and encouraging adequate biofiltration, but recently have begun augmenting filtration layers with media specifically suited to chemically reduce redox of incoming pollutant streams. Rain gardens are beneficial for many reasons: improve water quality by filtering runoff, provide localized flood control, are aesthetically pleasing, and provide interesting planting opportunities. They also encourage wildlife and biodiversity, tie together buildings and their surrounding environments in attractive and environmentally advantageous ways, and provide significant partial solutions to important environmental problems that affect us all. A rain garden provides a way to use and optimize any rain that falls, reducing or avoiding the need for irrigation. They allow a household or building to deal with excessive rainwater runoff without burdening the public storm water systems. Rain gardens differ from retention basins, in that the water will infiltrate the ground within a day or two. This creates the advantage that the rain garden does not allow mosquitoes to breed. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「A rain garden is a planted depression or a hole that allows rainwater runoff from impervious urban areas, like roofs, driveways, walkways, parking lots, and compacted lawn areas, the opportunity to be absorbed. This reduces rain runoff by allowing stormwater to soak into the ground (as opposed to flowing into storm drains and surface waters which causes erosion, water pollution, flooding, and diminished groundwater).University of Rhode Island. Healthy Landscapes Program. (“Rain Gardens: Enhancing your home landscape and protecting water quality.” ) They should be designed for specific soils and climates.Dussaillant et al. () Journal of Hydrologic Engineering The purpose of a rain garden is to improve water quality in nearby bodies of water and to ensure that rainwater becomes available for plants as groundwater rather than being sent through stormwater drains straight out to sea. Rain gardens can cut down on the amount of pollution reaching creeks and streams by up to 30%.Native and adapted plants are recommended for rain gardens because they are more tolerant of one’s local climate, soil, and water conditions; have deep and variable root systems for enhanced water infiltration and drought tolerance; habitat value and diversity for local ecological communities; and overall sustainability once established. There can be trade-offs associated with using native plants, including lack of availability for some species, late spring emergence, short blooming season, and relatively slow establishment. The plants — a selection of wetland edge vegetation, such as wildflowers, sedges, rushes, ferns, shrubs and small trees — take up excess water flowing into the rain garden. Water filters through soil layers before entering the groundwater system. Root systems enhance infiltration, maintain or even augment soil permeability, provide moisture redistribution, and sustain diverse microbial populations involved in biofiltration.B.C. Wolverton, Ph.D., R.C. McDonald-McCaleb (1986). (“Biotransformation of Priority Pollutants Using Biofilms and Vascular Plants.” ) ''Journal Of The Mississippi Academy Of Sciences.'' Vol. XXXI, pp. 79-89. Also, through the process of transpiration, rain garden plants return water vapor to the atmosphere.A. Dussaillant, Ph.D., et al. (2005). () ''Water Science & Technology: Water Supply journal.'' Vol. 5, pp. 173-179. A more wide-ranging definition covers all the possible elements that can be used to capture, channel, divert, and make the most of the natural rain and snow that falls on a property. The whole garden can become a rain garden, and each component of the whole can become a small-scale rain garden in itself.==Restoring the water cycle and mitigating urbanization==In developed areas, natural depressions where storm water would pool, are filled in. The surface of the ground is often leveled or paved. Storm water is directed into storm drains which often may cause overflows of combined sewer systems or poisoning, erosion or flooding of waterways receiving the storm water runoff.Kuichling, E. 1889. “The relation between the rainfall and the discharge of sewers in populous districts.” ''Trans. Am. Soc. Civ. Eng.'' 20, 1–60.Leopold, L. B. 1968. (“Hydrology for urban land planning: A guidebook on the hydrologic effects of urban land use.” ) ''Geological Survey Circular'' 554. United States Geological Survey.Waananen, A. O. 1969. “Urban effects on water yield” in W. L. Moore and C. W. Morgan (eds), ''Effects of Watershed Changes on Streamflow.'' University of Texas Press, Austin and London. Redirected storm water is often warmer than the groundwater normally feeding a stream, and has been linked to upset in some aquatic ecosystems primarily through the reduction of dissolved oxygen (DO). Storm water runoff is also a source of a wide variety of pollutants washed off hard or compacted surfaces during rain events. These pollutants include volatile organic compounds, pesticides, herbicides, hydrocarbons and trace metalsNovotny, V. and Olem, H. 1994. “Water Quality: Prevention, Identification, and Management of Diffuse Pollution.” Van Nostrand Reinhold, New York. Rain gardens are designed to capture the initial flow of storm water and reduce the accumulation of toxins flowing directly into natural waterways through ground filtration. They also reduce energy consumption. For example, “the cumulative storage capacity of these rain gardens exceeds a conventional stormwater’s system’s by 10 times.” The National Science Foundation, the United States Environmental Protection Agency, and a number of research institutions are presently studying the impact of augmenting rain gardens with materials capable of capture or chemical reduction of the pollutants to benign compounds.Rain gardens are often located near a building’s roof drainpipe (with or without rainwater tanks). Most rain gardens are designed to be an endpoint of drainage with a capacity to percolate all incoming water through a series of soil or gravel layers beneath the surface plantings. A French drain may be used to direct a portion of the rainwater to an overflow location for heavier rain events. By reducing peak stormwater discharge, rain gardens extend hydraulic lag time and somewhat mimic the natural water cycle displaced by urban development and allow for groundwater recharge. While rain gardens always allow for restored groundwater recharge, and reduced stormwater volumes, they may also increase pollution unless remediation materials are included in the design of the filtration layers .The primary challenge of rain garden design centers on calculating the types of pollutants and the acceptable loads of pollutants the rain garden's filtration system can handle during storm-water events. This challenge is specifically acute when a rain event occurs after a longer dry period. The initial storm water is often highly contaminated with the accumulated pollutants from dry periods. Rain garden designers have previously focused on finding robust native plants and encouraging adequate biofiltration, but recently have begun augmenting filtration layers with media specifically suited to chemically reduce redox of incoming pollutant streams.Rain gardens are beneficial for many reasons: improve water quality by filtering runoff, provide localized flood control, are aesthetically pleasing, and provide interesting planting opportunities. They also encourage wildlife and biodiversity, tie together buildings and their surrounding environments in attractive and environmentally advantageous ways, and provide significant partial solutions to important environmental problems that affect us all.A rain garden provides a way to use and optimize any rain that falls, reducing or avoiding the need for irrigation. They allow a household or building to deal with excessive rainwater runoff without burdening the public storm water systems. Rain gardens differ from retention basins, in that the water will infiltrate the ground within a day or two. This creates the advantage that the rain garden does not allow mosquitoes to breed.」の詳細全文を読む スポンサード リンク
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