Rain gardens

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This article is about planted installations designed to capture surface runoffThat potion of the water precipitated onto a catchment area, which flows as surface discharge from the catchment area past a specified point.Water from rain, snow melt, or irrigation that flows over the land surface. in an amended soil.

For more highly engineered systems, see Bioretention.
ShrubsShrubsStoneMulchAmended soilSandPerennialsPerennialsGrassesGrassesGrassesGrassesDownspout disconnectionDownspout disconnectionPerennials
This is an imagemap of a rain gardenA lot level bioretention cell designed to receive and detain, infiltrate and filter runoff, typically used for discharge from downspouts., clicking on the components will load the appropriate article.
Disconnected downspout routing water into a rain gardenA lot level bioretention cell designed to receive and detain, infiltrate and filter runoff, typically used for discharge from downspouts..

Overview

Rain gardens capture roof, lawn and driveway runoffThat potion of the water precipitated onto a catchment area, which flows as surface discharge from the catchment area past a specified point.Water from rain, snow melt, or irrigation that flows over the land surface. from low to medium density residential lots. These can be simple gardens constructed by the homeowner as a retrofit, or they can be professionally designed into a residential development.

Rain gardens are ideal for:

  • Capturing the flow from disconnected downspouts
  • Community design/build projects for raising awareness about stormwater capture and functional landscapes

The fundamental components of a rain gardenA lot level bioretention cell designed to receive and detain, infiltrate and filter runoff, typically used for discharge from downspouts. are:

Additional components may include:

  • A splash pad of stone to prevent the downspout flow from eroding the soil
  • A simple overflow swale to another area of the garden

Planning Considerations

Raingardens look like typical gardens. However, their infiltration and bioretention functions are much greater than normal gardens. By landscaping areas to include a surface depression of approximately 150 mm, rain gardens allow runoffThat potion of the water precipitated onto a catchment area, which flows as surface discharge from the catchment area past a specified point.Water from rain, snow melt, or irrigation that flows over the land surface. from residential properties to collect and to easily absorb into the ground. Within the rain gardenA lot level bioretention cell designed to receive and detain, infiltrate and filter runoff, typically used for discharge from downspouts., special types of soil, 'filter media' or soil amendments increase the amount of water absorbed by the garden and infiltrated into native soils.

Location is very important to a functioning rain gardenA lot level bioretention cell designed to receive and detain, infiltrate and filter runoff, typically used for discharge from downspouts.. When looking at potential locations, look for low areas where runoffThat potion of the water precipitated onto a catchment area, which flows as surface discharge from the catchment area past a specified point.Water from rain, snow melt, or irrigation that flows over the land surface. can be easily be directed into the garden. Rain gardens are a great option for residential LIDLow Impact Development. A stormwater management strategy that seeks to mitigate the impacts of increased urban runoff and stormwater pollution by managing it as close to its source as possible. It comprises a set of site design approaches and small scale stormwater management practices that promote the use of natural systems for infiltration and evapotranspiration, and rainwater harvesting. retrofits because homeowners can customize the garden to suit their desired styles. They can be planted with a variety of vegetation including shrubs, grasses and flowers.

A well-designed rain gardenA lot level bioretention cell designed to receive and detain, infiltrate and filter runoff, typically used for discharge from downspouts. can be maintained with minimal care, which is a great marketing point for persuading homeowners. In the first two years, the plants will need watering to ensure they become established. After this establishment period, the garden should only need simple maintenance, e.g. weeding.

Design

Plant Selection

The design of a rain gardenA lot level bioretention cell designed to receive and detain, infiltrate and filter runoff, typically used for discharge from downspouts. allows for several different planting zones.

  • A variety of plant material can be selected based on the desired aesthetic, including turf grass, ornamental grasses and perennial flowers, shrubs, and trees.
  • The aesthetic can range from very naturalistic to quite formal, depending on the planting plan.
  • Vegetation must also be capable of tolerating prolonged wet and dry periods unless an irrigationHuman application of water to agricultural or recreational land for watering purposes. City of Toronto Wet Weather Flow Management November 2006 47 plan is in place
  • If the facility is intended to be relatively inconspicuous, then the tallest plant material should be placed into the deepest part of the rain gardenA lot level bioretention cell designed to receive and detain, infiltrate and filter runoff, typically used for discharge from downspouts.. Otherwise, choose taller plants for the back of the garden tapering the height down to the front of the garden. [1].


Since rain gardens are typically smaller scale homeowner projects smaller stock plants may be considered. Smaller containers may be easier to purchase, transport, and plant, but it may take longer to have a fully vegetated garden. Plant material per Canadian Standards for Nursery Stock, Eighth Edition. Seed planting is not recommended for rain gardens. Plants should be container grown, balled and burlapped or wire basket.

Below are recommended plant sizes for planting rain gardenA lot level bioretention cell designed to receive and detain, infiltrate and filter runoff, typically used for discharge from downspouts. features:

Deciduous Shrubs - 60 - 80 cm height

Coniferous Shrubs / Broadleaf Evergreens - 40 cm spread (roughly #3 or 3 gal. container)

Perennials/Grasses - 15 cm to #1 or 1 gal. container stock

Ground Cover/ Vines - 10 cm to #1 or 1 gal. container stock

Hydric Zone Criteria

Low Zone Often referred to as the extended detentionA stormwater design features that provides for the gradual release of a volume of water in order to increase settling of pollutants and protect downstream channels from frequent storm events. or shoreline fringe area. This area is frequently inundated during storm events, and is well-drained between rainfall events.
Mid Zone Often referred to as the floodfringe area. This zone is inundated less frequently (2 – 100 year storm events) and has periodically high levels of moisture in the soil. The ecology of this zone is a transition from the Mineral Meadow Marsh/Beach-type community to an upland community.
High Zone Often referred to as upland area. The ecology of this zone is terrestrial due to its elevation in relation to the filter bed. The zone most closely resembles a Cultural Meadow or a Cultural Thicket community, depending on the mix of grasses, herbaceous material, shrubs and trees utilized.
Low Zone
  • Mineral Meadow Marsh plant community
  • Grasses, Sedges, rushes, wildflowers, ferns and shrubs that have an ‘Obligate’ to ‘Facultative’ designation
  • WetlandA vegetated area such as a bog, fen, marsh, or swamp, where the soil or root zone is saturated for part of the year. ‘Obligate’ species that are flood tolerant as they will persist in average years and flourish in wetter years.
  • Plants that are likely to occur in wetlands or adjacent to wetlands.
  • Plants with dense root structure and /or vegetative cover are favoured for their ability to act as pollution filters and tendency to slow water velocity
  • Be advised these practices are not constructed wetlands and are designed to fully drain within 48 hours.

Mid Zone

  • Plants able to survive in soils that are seasonally saturated, yet can also tolerate periodic drought.
  • Species include grasses and groundcovers, as well as low shrub species.

High Zone

  • Plants should have deep roots for structure, be drought-tolerant and capable of withstanding occasional soil saturation.
  • Trees and large shrubs planted in this zone will aid in the infiltration and absorption of stormwaterSurface runoff from at-grade surfaces, resulting from rain or snowmelt events..
  • This area can be considered a transition area into other landscape or site areas.
  • A variety (min. five) species should be used to prevent a monoculture.

Landscaping Design Consideration

  • In natural areas, a diversity of plant types not only adds beauty but also create a thick underground root matrix that keeps the entire plant community in balance. In fact, 80% of the plant mass in native prairie communities is underground. Once the rain gardenA lot level bioretention cell designed to receive and detain, infiltrate and filter runoff, typically used for discharge from downspouts. has matured and your sedges, rushes and grasses have established a deep, thick root system, there will be less change in species location from year to year, and weeds will naturally decline. [2].
  • Smooth out any sharp corners to create flow in your garden.
  • Neat edges can be established using pavers, walls or bands of turf create an attractive amenity within the residential landscape.


See Also

External Links


  1. Peel Fusion Landscaping
  2. Appendix D - Low Impact Development Concepts, Rain Gardens: A how-to manual for homeowners, Wisconsin Department of Natural Resources, Page 15