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Green infrastructures have a lot of benefits and can be implemented during construction or as retrofits. On this page you can browse summaries on green infrastructures practices.

PRACTICE SUMMARY
A rain garden, or bioretention area, is a landscaping feature designed to allow stormwater runoff to collect, settle, then infiltrate into the ground. Rain gardens should be placed in natural or deliberately built depressions where stormwater from impervious surfaces drains or collects. Siting the rain garden requires an analysis of stormwater flow patterns, natural slopes, and impervious surface routes. As well, a place-based study of soil infiltration rates and plants that will grow well in your micro-climate will maximize the function and efficiency of your garden. (Road sides, parking lots, side walks, residential yards, and roof downspouts)

PRIMARY FUNCTION(S):
Detention, Infiltration, Treatment, and Evapotranspiration.

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Benefits

  • Reduced runoff volume mean of 90% (Driscoll 2015)
  • Reduces pollutants in runoff
  • Increases infiltration
  • Easy to retrofit and flexible to fit into landscape
  • Biorention areas cost less than traditional structural stormwater systems by reducing the use of concrete and piping

Constraints/Design Considerations

  • Small gardens have less impact on volume reduction
  • Requires landscaping and maintanence
  • Should be installed at least 10 feet from a buildingʻs foundation

ADDITIONAL WEB MATERIAL

  • Bioretention Literary Review is a collection of over 16 years of bioretention research prepared by Robert Brown from North Carolina State University.
  • The Urban Design Tools summarizes stormwater runoff treatment and volume reduction benefits of biorention.
  • Hui o Ko’olaupoko is a non-profit entity who assist in volunteer rain garden installation in Windward O’ahu.
  • Hawai’i Rain Garden Manual (pdf) by Hui o Koolaupoko.

Bioswale

PRACTICE SUMMARY

Bioswales are vegetated, mulched, or xeriscaped channels that provide treatment and retention as they move stormwater from one place to another.  Vegetated swales slow, infiltrate, and filter stormwater flows. As linear features, vegetated swales are particularly suitable along streets, parking lots and along the perimeter of large lots.

 

PRIMARY FUNCTION(S):

Conveyence, Infiltration, Treatment, and Evapotranspiration.

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Benefits

  • Reduced runoff volume mean of 27% (Driscoll 2015)
  • Vegetation Reduces pollutants in runoff
  • Increases infiltration

Constraints/Design Considerations

  • Because the bioswale is a conveyance system, the channel must be able to transport stormwater without flooding.
  • Design should be developed for the storm events that most significantly contribute to CSOs, hydraulic overloads, and runoff problems for a given area. (EPA, 2000)

ADDITIONAL WEB MATERIAL

  • Stormwater BMP, a summary of bioswales by the EPA.
  • Stormwater Technology Factsheet (pdf) includes details on the design and benefits of vegatate swales, by the EPA.
  • Biofilters for Stormwater Discharge Pollution Removal (pdf) by State of Oregon Department of Environmental Quality.

Permeable Pavements

PRACTICE SUMMARY

Permeable pavements are paving materials that allow stormwater to infiltrate, treat, and/or store rainwater where it falls. Permeable pavements may be constructed from pervious concrete, porous asphalt, permeable interlocking pavers, and several other materials. These pavements are particularly cost effective where land values are high and where flooding or icing is a problem.

These pavements can replace many impervious pavements with low load bearing criteria.

 

PRIMARY FUNCTION(S):

Infiltration.

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Benefits

  • Reduced runoff volume mean of 58% (Driscoll 2015)
  • Increases infiltration
  • Because these pavements replace conventional impervious asphalts and concretes, they do not require additional alloted space as a swale or rain garden might.

Constraints/Design Considerations

  • Voids in porous asphalt can become clogged by sand or other fine sediments.
  • Pervious concrete cost can be high where specialized vendors are absent.
  • Porous asphalt may be percieved as looking “less finished” or “more coarse” when compared to convential asphalt. (Haffner, 2007)

ADDITIONAL WEB MATERIAL

Flow-Through Planters

PRACTICE SUMMARY

Flow-Through Planters are GI elements that can be installed along the “green zone” of a street or in the “dead space” of a parking lot. They have vertical walls and open or closed bottoms that allow captured stormwater to be absorbed into the ground. Planter boxes are ideal for space-limited sites in dense urban areas and as landscaping for streets. These features work well in areas with poor drainage and places where stormwater drains from rooftop gutters.

 

PRIMARY FUNCTION(S):

Flow reduction, Treatment, and Evapotranspiration.

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Benefits

  • Lessens stormwater flow and pooling
  • Reduces erosion
  • Reduces stormwater volume
  • Filters pollutants from runoff

Constraints/Design Considerations

  • Must be placed at least 10 feet from building foundations

ADDITIONAL WEB MATERIAL

  • A fact sheet (pdf) from Oregon State University outlines the basics on flow-through planter function, design and maintenance.

Green Roofs

PRACTICE SUMMARY

Green roofs are a type of garden designed for roof top installation. The key components of a green roof include drought resistant plants, a waterproof layer, a drainage layer, a filter membrane, a growing medium, and a vegetative layer. There are two types of green roofs, extensive and intensive. Extensive roofs use plants with shallow roots that only require a growing medium of less than 6 inches deep. Intensive roofs use growing mediums that are greater than 6 inches thick and are ideal for deep rooting plants such as trees.

 

PRIMARY FUNCTION(S):

Evapotranspiration.

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Benefits

  • Reduced runoff volume mean of 73% (Driscoll 2015)
  • Evapotranspirate rainfall
  • Reduces and mitigates urban heat island effects
  • Regulates building temperatures

Constraints/Design Considerations

  • Regular landscape maintenance is needed to varying degrees after installation.
  • Limited to roof slopes less that 20 degrees.
  • Additional support may be needed to bear added weight.
  • Irrigation required to establish plants and maintain them during dry periods.
  • High upfront cost

ADDITIONAL WEB MATERIAL

Loʻi Kalo

PRACTICE SUMMARY

Loʻi kalo are ponds used for wetlands kalo (taro) cultivation. Ditches called ʻauwai are used to connect the loʻi to a nearby stream. The water from the diverted stream enters the loʻi at its uppermost inlet then flows through terraces until it is finally discharged back into the stream. Loʻi kalo and ʻauwai are important to traditional Hawaiian agriculture and watershed management.

 

PRIMARY FUNCTION(S):

Detention and Evapotranspiration.

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Benefits

  • Reduce stream flow velocity, allowing for increased infiltration
  • Increase evapotranspiration

Constraints/Design Considerations

  • Because the effluent from loʻi can contain sediment and nutrients, considerations for the outflow should be addressed.
  • Measurements of quality and quantity parameters such as filtration, temperature, and discharge volume are dependent on location and design of the lo’i.

Rain Water Harvesting and Reuse

PRACTICE SUMMARY

It is estimated that 30,000 to 60,000 people in Hawai’i depend on a rainwater catchment system for their water needs (Macomber, 2010). The collection and reclamation of stormwater may be employed on varying scales. On private residential or commercial lots, water catchment systems utilize surfaces like rooftops to direct rainfall into storage tanks. The stored water can then be used for a variety of purposes including irrigation, showers, and toilets. There are four key components to a harvesting system: collection, storage, treatment, and delivery.

 

PRIMARY FUNCTION(S):

Water Conservation

rainwater catchment system

Benefits

  • Reduces the volume of runoff by 25-45% (Wakumoto 2015).
  • Lessens municipal potable water use for irrigation and other grey water uses.

Constraints/Design Considerations

  • Uses for harvest water are limited by local water quality standards.
  • Regular inspection and cleaning of catchment area are recommended if a filtration system is not installed.

ADDITIONAL WEB MATERIAL

Green Streets, Sidewalks, and Parking Lots

PRACTICE SUMMARY

Many of these GI practices (flow-through planters, permeable pavers, swales, and rain gardens) can be incorporated into how we design streets, sidewalks, and parking lots. GI elements maximize our land use by having streets and parking lots that function as both support for vehicular travel and control of storm runoff. These elements can be installed in most streets, and are incredibly useful in urban areas where there is not enough space for stormwater management facilities.

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Benefits

  • Reduces the volume of runoff.
  • Filters pollutants from runoff.
  • Increases evapotranspiration.
  • Increase infiltration.

Constraints/Design Considerations

  • Planning and design to use curb cuts, end stops, and sloping to channel stormwater into the planter boxes needed before installation.

ADDITIONAL WEB MATERIAL

  • LATIS – Suburban Street Stormwater Retrofitting by Andrew Fox is an online guide to stormwater management in suburban areas.
  • Smart Trees Pacific supports projects and strategies for increase the use of trees from stormwater management in urban areas. This includes planting trees along roads and parking lots.

Driscoll, C.T., Eger, C.G., Chandler, D.G., Davidson, C. I., Roodsari, B.K., Flynn, C.D., Lambert, K.F., Bettez, N.D., Groffman, P.M. 2015. Green Infrastructure: Lessons from Science and Practice. A publication of the Science Policy Exchange. 32 pages.

Wakumoto, R. (2015). UPDATE ON THE CITY ’ S NPDES MS4 PERMIT PROGAM CHALLENGES WITH ITS MS4 PERMIT REQUIREMENTS Non-Point Source Pollution, (May).