Rain garden
Rain gardens, also called bioretention facilities, are one of a variety of practices designed to increase rain runoff reabsorption by the soil. They can also be used to treat polluted
Rain garden plantings commonly include
Rain gardens are beneficial for many reasons; they improve water quality by filtering runoff, provide localized
History
The first rain gardens were created to mimic the natural water retention areas that developed before urbanization occurred. The rain gardens for residential use were developed in 1990 in
Some de facto rain gardens predate their recognition by professionals as a significant LID (
Urban runoff mitigation
Effects of urban runoff
In developed urban areas, naturally occurring
Stormwater management systems
Stormwater management occurs on a watershed scale to prevent downstream impacts on urban water quality.[12] A watershed is maintained through the cyclical accumulation, storage, and flow of groundwater.[2] Naturally occurring watersheds are damaged when they are sealed by an impervious surface, which diverts pollutant-carrying stormwater runoff into streams. Urban watersheds are affected by greater quantities of pollutants due to the consequences of anthropogenic activities within urban environments.[13] Rainfall on impermeable surfaces accumulates surface runoff containing oil, bacteria, and sediment that eventually makes its way to streams and groundwater.[2] Stormwater control strategies such as infiltration gardens treat contaminated surface runoff and return processed water to the underlying soil, helping to restore the watershed system. The effectiveness of stormwater control systems is measured by the reduction of the amount of rainfall that becomes runoff (retention), and the lag time (rate of depletion) of the runoff.[14] Even rain gardens with small capacities for daily infiltration can create a positive cumulative impact on mitigating urban runoff. Increasing the number of permeable surfaces by designing rain gardens reduces the amount of polluted stormwater that reaches natural bodies of water and recharges groundwater at a higher rate.[15] Additionally, adding a rain garden to a site that experiences excessive rainwater runoff mitigates the water quantity load on public stormwater systems.[citation needed]
The bioretention approach to water treatment, and specifically rain gardens in this context, is two-fold: to utilize the natural processes within landscapes and soils to transport, store, and filter stormwater before it becomes runoff, and to reduce the overall amount of impervious surface covering the ground that allow for contaminated urban runoff.
Bioretention
The concept of LID (low-impact design) for stormwater management is based on
Water treatment process
Bioretention controls the stormwater quantity through interception, infiltration, evaporation, and transpiration.
Stormwater quality can be controlled by bioretention through settling, filtration, assimilation, adsorption, degradation, and decomposition.[16] When water pools on top of a bioretention feature, suspended solids and large particles will settle out. Dust particles, soil particles, and other small debris are filtered out of the water as it moves downward through the soil and interspersed plant roots. Plants take up some of the nutrients for use in their growth processes, or for mineral storage. Dissolved chemical substances from the water also bind to the surfaces of plant roots, soil particles, and other organic matter in the substrate and are rendered ineffective. Soil microorganisms break down remaining chemicals and small organic matter and effectively decompose the pollutants into a saturated soil matter.[20]
Even though natural water purification is based on the design of planted areas, the key components of bioremediation are the soil quality and microorganism activity. These features are supported by plants, which create secondary pore space to increase soil permeability, prevent soil compaction through complex root structure growth, provide habitats for the microorganisms on the surfaces of their roots, and transport oxygen to the soil.[20]
Design
Stormwater garden design encompasses a wide range of features based on the principles of bioretention. These facilities are then organized into a sequence and incorporated into the landscape in the order that rainfall moves from buildings and permeable surfaces to gardens, and eventually, to bodies of water. A rain garden requires an area where water can collect and infiltrate, and plants can maintain infiltration rates, diverse microorganism communities, and water storage capacity. Because infiltration systems manage storm water quantity by reducing storm water runoff volumes and peak flows, rain garden design must begin with a site analysis and assessment of the rainfall loads on the proposed bioretention system.[13] This will lead to different knowledge about each site, which will affect the choice of plantings and substrate systems. At a minimum, rain gardens should be designed for the peak runoff rate during the most severe expected storm. The load applied on the system will then determine the optimal design flow rate.[15]
Existing gardens can be adapted to perform like rain gardens by adjusting the landscape so that downspouts and paved surfaces drain into existing planting areas. Even though existing gardens have loose soil and well-established plants, they may need to be augmented in size and/or with additional, diverse plantings to support a higher infiltration capacity. Also, many plants do not tolerate saturated roots for long and will not be able to handle the increased flow of water. Rain garden plant species should be selected to match the site conditions after the required location and storage capacity of the bioretention area are determined. In addition to mitigating urban runoff, the rain garden may contribute to urban habitats for native
Rain gardens are at times confused with
Soil and drainage
Collected water is filtered through the strata of soil or engineering growing soil, called substrate. After the soil reaches its saturation limit, excess water pools on the surface of the soil and eventually infiltrates the natural soil below. The bioretention soil mixture should typically contain 60% sand, 20% compost, and 20% topsoil. Soils with higher concentrations of compost have shown improved effects on filtering groundwater and rainwater.[23] Non-permeable soil needs to be removed and replaced periodically to generate maximum performance and efficiency if used in the bioretention system. The sandy soil (bioretention mixture) cannot be combined with a surrounding soil that has a lower sand content because the clay particles will settle in between the sand particles and form a concrete-like substance that is not conducive to infiltration, according to a 1983 study.[24] Compact lawn soil cannot harbor groundwater nearly as well as sandy soils, because the micropores within the soil are not sufficient for retaining substantial runoff levels.[16]
When an area's soils are not
Rain gardens are often located near a building's roof drainpipe (with or without
Vegetation
Typical rain garden plants are herbaceous perennials and grasses, which are chosen for their porous root structure and high growth rate.[16] Trees and shrubs can also be planted to cover larger areas on the bioretention site. Although specific plants are selected and designed for respective soils and climates,[27] plants that can tolerate both saturated and dry soil are typically used for the rain garden. They need to be maintained for maximum efficiency, and be compatible with adjacent land uses. Native and adapted plants are commonly selected for rain gardens because they are more tolerant of the local climate, soil, and water conditions; have deep and variable root systems for enhanced water infiltration and drought tolerance; increase habitat value, diversity for local ecological communities, and overall sustainability once established. Vegetation with dense and uniform root structure depth helps to maintain consistent infiltration throughout the bioretention system.[28] 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.
It is important to plant a wide variety of species so the rain garden is functional during all climatic conditions. It is likely that the garden will experience a gradient of moisture levels across its functional lifespan, so some drought tolerant plantings are desirable. There are four categories of a vegetative species’ moisture tolerance that can be considered when choosing plants for a rain garden. Wet soil is constantly full of water with long periods of pooling surface water; this category includes swamp and marsh sites. Moist soil is always slightly damp, and plants that thrive in this category can tolerate longer periods of flooding. Mesic soil is neither very wet nor very dry; plants that prefer this category can tolerate brief periods of flooding.[16] Dry soil is ideal for plants that can withstand long dry periods. Plantings chosen for rain gardens must be able to thrive during both extreme wet and dry spells, since rain gardens periodically swing between these two states. A rain garden in temperate climates will unlikely dry out completely, but gardens in dry climates will need to sustain low soil moisture levels during periods of drought. On the other hand, rain gardens are unlikely to suffer from intense waterlogging, since the function of a rain garden is that excess water is drained from the site. Plants typically found in rain gardens are able to soak up large amounts of rainfall during the year as an intermediate strategy during the dry season.[16] Transpiration by growing plants accelerates soil drying between storms. Rain gardens perform best using plants that grow in regularly moist soils, because these plants can typically survive in drier soils that are relatively fertile (contain many nutrients).
Chosen vegetation needs to respect site constraints and limitations, and especially should not impede the primary function of bioretention. Trees under power lines, or that up-heave sidewalks when soils become moist, or whose roots seek out and clog drainage tiles can cause expensive damage. Trees generally contribute to bioretention sites the most when they are located close enough to tap moisture in the rain garden depression, yet do not excessively shade the garden and allow for evaporation. That said, shading open surface waters can reduce excessive heating of vegetative habitats. Plants tolerate inundation by warm water for less time than they tolerate cold water because heat drives out
Pollutant removal
Rain gardens are designed to capture the initial flow of stormwater and reduce the accumulation of
The primary challenge of rain garden design is predicting the types of pollutants and the acceptable loads of pollutants the rain garden's filtration system can process during high impact storm events. Contaminants may include organic material, such as animal waste and oil spills, as well as inorganic material, such as heavy metals and fertilizer
Projects
This section needs additional citations for verification. (June 2021) |
Australia
- Healthy Waterways Raingardens Program promotes a simple and effective form of stormwater treatment, and aims to raise peoples' awareness about how good stormwater management contributes to healthy waterways. The program encourages people to build rain gardens at home, and has achieved its target is to see 10,000 rain gardens built across Melbourne by 2013.[30]
- Melbourne Water's database of Water Sensitive Urban Design projects, including 57 case studies relating to rain gardens/bioretention systems. Melbourne Water is the Victorian State Government agency responsible for managing Melbourne's water supply catchments.[31]
- Water By Design is a capacity building program that supports the uptake of Water Sensitive Urban Design, including rain gardens, in South East Queensland. It was established by the South East Queensland Healthy Waterways Partnership in 2005, as an integral component of the SEQ Healthy Waterways Strategy.[32]
United Kingdom
- The Wildfowl and Wetlands Trust's London Wetland Centre includes a rain garden.[33]
- Islington London Borough Council commissioned sustainable drainage consultants Robert Bray Associates to design a pilot rain garden in the Ashby Grove development which was completed in 2011. This raingarden is fed from a typical modest domestic roof catchment area of 30m² and is designed to demonstrate how simple and cost effective domestic rain gardens are to install. Monitoring apparatus was built into the design to allow Middlesex University to monitor water volumes, water quality, and soil moisture content. The rain garden basin is 300mm deep and has a storage capacity of 2.17m³ which is just over the volume required to store runoff from the roof catchment in a 1 in 100 storm plus 30% allowance for climate change.[34][35]
- The Day Brook Rain Garden Project has introduced a number of rain gardens into an existing residential street in Sherwood, Nottingham[36]
United States
- The 12,000 rain garden campaign for Puget Sound is coordinating efforts to build 12,000 rain gardens in the Puget Sound Basin of Western Washington by 2016. The 12,000 rain gardens website provides information and resources for the general public, landscape professionals, municipal staff, and decision makers. By providing access to the best current guidance, easy-to-use materials, and a network of trained "Rain Garden Mentor" Master Gardeners, this campaign seeks to capture and cleanse over 200 Million gallons of polluted runoff each year, and thereby significantly improve Puget Sound's water quality.[37]
- Maplewood, Minnesota has implemented a policy of encouraging residents to install rain gardens. Many neighborhoods had swales added to each property, but installation of a garden at the swale was voluntary. The project was a partnership between the City of Maplewood, University of Minnesota Department of Landscape Architecture, and the Ramsey Washington Metro Watershed District. A focus group was held with residents and published so that other communities could use it as a resource when planning their own rain garden projects.
- Some local governmental organizations offer local grants for residents to install raingardens. In Dakota County, Minnesota, the Dakota County Soil and Water Conservation District offers $250 grants and technical assistance through their Landscaping for Clean Water program to encourage residents to install residential raingardens.
- In Seattle, a prototype project, used to develop a plan for the entire city, was constructed in 2003. Called SEA Street, for Street Edge Alternatives, it was a drastic facelift of a residential street. The street was changed from a typical linear path to a gentle curve, narrowed, with large rain gardens placed along most of the length of the street. The street has 11% less impervious surface than a regular street. There are 100 evergreen trees and 1100 shrubs along this 3-block stretch of road, and a 2-year study found that the amount of stormwater which leaves the street has been reduced by 99%.[38]
- 10,000 Rain Gardens is a public initiative in the Kansas City, Missouri metro area. Property owners are encouraged to create rain gardens, with an eventual goal of 10,000 individual gardens.
- The Washtenaw County, homeowners can volunteer for the Water Resources Commissioner's Rain Garden program, in which volunteers are annually selected for free professional landscape design. The homeowners build the gardens themselves as well as pay for landscaping material. Photos of the gardens as well as design documents and drainage calculations are available online.[41] The Washtenaw County Water Resource Commissioner's office also offers yearly in person and online Master Rain Gardener classes to help guide those interested in the rain garden design, building, and upkeep process.[42]
- Portland, Oregon, has established a Clean River Rewards program, to encourage residents to disconnect downspouts from the city's combined sewer system and create rain gardens. Workshops, discounts on storm water bills, and web resources are offered.[43]
- In Delaware, several rain gardens have been created through the work of the University of Delaware Water Resources Agency, and environmental organizations, such as the Appoquinimink River Association.[44]
- In New Jersey, the Rutgers Cooperative Extension Water Resources Program has installed over 125 demonstration rain gardens in suburban and urban areas. The Water Resources Program has begun to focus on using rain gardens as green infrastructure in urban areas, such as Camden and Newark to help prevent localized flooding, combined sewer overflows, and to improve water quality. The Water Resources Program has also revised and produced a rain garden manual in collaboration with The Native Plant Society of New Jersey.[45]
- According to the Massachusetts Department of Environmental Protection, rain gardens may remove 90% of total suspended solids, 50% of nitrogen, and 90% of phosphorus.[18]
- Dr. Allen P. Davis is an environment and civil engineering professor at the University of Maryland, College Park. For the past 20 years, Davis and his team have been studying the effectiveness of rain gardens. For their research, they constructed two rain gardens on campus near the Anacostia River watershed in the Fall of 2001.[46] Much of the runoff from the University of Maryland campus, a member of the Anacostia Watershed Restoration Partnership, ends up in the Anacostia River feeding into the Chesapeake Bay. This research finds rain gardens to be a very effective method of water capture and filtration, encouraging others in the Chesapeake Bay Watershed to implement rain gardens.
- Davis' research showed that rain gardens aid in the capturing and bio-degradation of pollutants such as suspended solids, bacteria, metals, oil, and grease.
- Water quality analyzed at the University of Maryland showed a significant increase in water clarity after rain garden filtration.[47]
- There is a rain garden at the Center for Young Children (CYC) at University of Maryland designed by students from the Department of Plant Science and Landscape Agriculture. The rain garden allows teachers at the CYC to educate future students on sustainability.[48]
China
- At the University of Technology in Xi'an, China, a rain garden was built to observe and study over four years. This study showed that over four years, there were 28 large storm events in Xi'an. Within these 28 storms, the rain garden was able to retain the rainfall from a majority of the storms. Only 5 of these storms caused the rain garden to overflow.[49]
- Rain Gardens in this sub-humid loess region of Xi'an China, are Low Impact Developments (LID).[49]
- China plans to implement a sponge city program in response to urban flooding. This program will prioritize the natural environment and will include rain gardens, green roofs, wetlands and more permeable surfaces to slow down storm water retention.[50]
See also
References
- ^ "Rain Gardens". Soak Up the Rain. EPA. 2016-04-28.
- ^ OCLC 181092577.
- ^ "Evapotranspiration and the Water Cycle". www.usgs.gov. Retrieved 2019-08-16.
- ^ B.C. Wolverton, Ph.D., R.C. McDonald-McCaleb (1986). “Biotransformation of Priority Pollutants Using Biofilms and Vascular Plants.” Archived April 7, 2009, at the Wayback Machine Journal of the Mississippi Academy of Sciences. Vol. XXXI, pp. 79-89.
- ^ University of Rhode Island. Healthy Landscapes Program. “Rain Gardens: Enhancing your home landscape and protecting water quality.” Archived 2015-10-23 at the Wayback Machine
- ^ a b c "Urban Runoff" (PDF). Nonpoint Source News-Notes. No. 42. Washington, D.C.: U.S. Environmental Protection Agency (EPA). August 1995. Archived from the original (PDF) on 2012-07-07.
- ^ a b Wisconsin Natural Resources (magazine). “Rain Gardens Made One Maryland Community Famous.” February 2003.
- ^ 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.
- ^ Novotny, V. and Olem, H. 1994. "Water Quality: Prevention, Identification, and Management of Diffuse Pollution." Van Nostrand Reinhold, New York.
- ISBN 978-0-309-12539-0.
- ^ ISBN 978-981-10-1659-2
- S2CID 114035530.
- ^ OCLC 34878752.
- ^ OCLC 551207971.
- ISBN 978-0-7844-7916-2.
- ^ a b "Bioretention Areas & Rain Gardens". megamanual.geosyntec.com. Retrieved 2022-03-08.
- S2CID 6051960.
- ^ a b "Are Rain Gardens Mini Toxic Cleanup Sites?". Sightline Institute. 2013-01-22. Retrieved 2022-03-09.
- ^ "The Beneficial Beauty of Rain Gardens – The Native Plant Herald". Retrieved 2022-03-09.
- ^ "Rain Gardens: Stormwater Management Solution". Horst Excavating. 2020-04-06. Retrieved 2022-03-09.
- S2CID 128987744.
- ^ "Archived copy" (PDF). Archived from the original (PDF) on 2013-12-12. Retrieved 2013-01-16.
{{cite web}}
: CS1 maint: archived copy as title (link) - ^ Sustainable City Network, Dubuque, IA (2011-02-21)."USGS: Rain Gardens Work Regardless of Soil Conditions."
- S2CID 11956259.
- ^ Dussaillant et al. [1] Journal of Hydrologic Engineering
- ISBN 978-981-287-244-9
- OCLC 695394144.
- ^ "Raingardens - Melbourne Water". melbournewater.com.au.
- ^ "Stormwater management (WSUD) - Melbourne Water". wsud.melbournewater.com.au.
- ^ "Home".
- ^ "WWT London - London Wetland Centre". www.wwt.org.uk.
- ^ "Robert Bray Associates Design Statement - Islington Council Public Records" (PDF). Islington Council.
- ^ "Ashby Grove residential retrofit rain garden, London". Susdrain. Retrieved 2013-12-02.
- ^ "Nottingham Green Streets – Retrofit Rain Garden Project". Susdrain. Archived from the original on 2013-10-02. Retrieved 2013-08-04.
- ^ "12,000 Rain Gardens - in Puget Sound". www.12000raingardens.org.
- ^ City of Seattle, Washington. Seattle Public Utilities. “Street Edge Alternatives (SEA Streets) Project.”
- ^ Rain Gardens of West Michigan, Grand Rapids, MI. “Rain Gardens of West Michigan”
- ^ Southeastern Oakland County Water Authority, Royal Oak, MI.
- ^ Washtenaw County, Michigan. “Rain Garden Virtual Tour”
- ^ "Master Rain Gardener Volunteer Program —". www.ewashtenaw.org. Retrieved 2016-09-01.
- ^ Clean River Rewards, Portland, Oregon. “Clean River Rewards.”
- ^ University of Delaware Cooperative Extension. “Rain Gardens in Delaware.”[permanent dead link]
- ^ "Water Resources Program at Rutgers NJAES". water.rutgers.edu.
- ^ "WATER QUALITY IMPROVEMENT USING RAIN GARDENS: UNIVERSITY OF MARYLAND STUDIES" (PDF).
- ^ "Rain Garden Pylon" (PDF).
- ^ "Center for Young Children Rain Garden | University of Maryland Office of Sustainability". sustainability.umd.edu. Retrieved 2017-09-17.
- ^ a b "Evaluating Retention Capacity of Infiltration Rain Gardens and Their Potential Effect on Urban Stormwater Management in the Sub-Humid Loess Region of China | Request PDF". ResearchGate. Retrieved 2019-04-18.
- ^ "Sponge City: Solutions for China's Thirsty and Flooded Cities". New Security Beat. 13 July 2017. Retrieved 2019-04-18.
Further reading
- Dunnett, Nigel and Andy Clayden. Rain Gardens: Sustainable Rainwater Management for the Garden and Designed Landscape. Timber Press: Portland, 2007. ISBN 978-0-88192-826-6
- Liu, Jia, David J. Sample, Cameron Bell and Yuntao Guan. 2014. “Review and Research Needs of Bioretention Used for the Treatment of Urban Stormwater”. Water, 6 (4): 1069–1099. “doi:10.3390/w6041069”
- Prince George's County. 1993. Design Manual for Use of Bioretention in Stormwater Management. Prince George's County, MD Department of Environmental Protection. Watershed Protection Branch, Landover, MD.
- Bioretention Manual (Report). Landover, MD: Prince George's County, Department of Environmental Resources. 2002. Archived from the original on 2009-04-22.
- Clar, Michael L.; Barfield, Billy J.; O'Connor, Thomas P. (September 2004). Stormwater Best Management Practice Design Guide, Volume 2: Vegetative Biofilters (Report). Edison, NJ: EPA. EPA 600/R-04/121A.
- Kraus, Helen, and Anne Spafford. Rain Gardening in the South: Ecologically Designed Gardens for Drought, Deluge & Everything in Between. Eno Publishers: Hillsborough, NC, 2009. ISBN 978-0-9820771-0-8
- Bray, B., Gedge, D., Grant, G., Leuthvilay, L. UK Rain Garden Guide. Published by RESET Development, London, 2012
External links
- Rain garden case study, Burnsville, MN (USA). 2004. Land & Water: 48(5).
- Water at the Grass Roots A brief introduction to Low Impact Development and rain gardens
- Creating a Rain Garden Details for construction of a rain garden with a link to a long plant list from Brooklyn Botanical Garden]
- Stormwater Tender project — Little Stringybark Creek, Victoria, Australia
- Rain Garden Design Templates for the Chesapeake Bay Watershed
- Wisconsin Department of Natural Resources — Rain Gardens
- Healthy Waterways Raingardens Program — Melbourne, Victoria, Australia