Green Infrastructure

Green Infrastructure

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In the context of infrastructure that helps reduce flood damage, cleans our watershed, and recharges our groundwater, it is helpful to distinguish between “grey” and “green” infrastructure.

“Grey” infrastructure has caused many problems in the Ala Wai Watershed (channelizing our streams with concrete, paving over the majority of surface area with roads, sidewalks, parking lots, and driveways), but can also be part of the solution (for example dams and retention basins to store flash flood water, pillars to catch debris, flood walls to protect important infrastructure). While grey infrastructure can help reduce flood hazard, it usually does little to improve water quality, recharge the groundwater, or beautify neighborhoods.

“Green” Infrastructure includes a number of infrastructure and landscaping strategies that can be applied across a watershed, many of which are in use in the Ala Wai Watershed to some extent. Below are the seven common types of green infrastructure, sometimes also referred to as “Low Impact Development” (LID) strategies.

1) Rain Garden – a deliberately built depression planted with vegetation that captures excess rain from your helps it soak into the ground. (Photocredit: Hui o Koʻolaupoko)

2) Bioretention – similar to rain gardens, bioretention areas are vegetated ditches that can store and filter rainwater running off from parking lots or other paved surfaces. (photo credit: EPA Water Protection Division, A Handbook for Local Governments)

3) Bioswale – a vegetated channel usually along roads or parking lots. Bioswales have a shallower gradient than conventional drainage ditches, slowing the water down to filter pollutants and allow it to soak into the ground. Deep bioswales, called planter boxes, require more construction, but can be more effective. (photo credit: EPA Water Protection Division, A Handbook for Local Governments)


4) Downspout Disconnection – disconnecting your downspout so the rain from your roof/raingutter doesn’t go straight into the storm sewers, but has a chance to filter into the ground in a vegetated area. Ideally, downspouts are connected to raingardens, planter boxes, or bioswales. (photo credit: Green Infrastructure for Homeowners Manual, City & County of Honolulu, BWS)

5) Green Roofs – covering flat roofs with a layer of vegetation (usually 2-6 inches thick) that soaks up rain, filters it, and then evaporates it. Most green roofs are located on industrial facilities or in dense urban areas with little space for other green infrastructure strategies. (photo credit: Green Infrastructure for Homeowners Manual, City & County of Honolulu, BWS)

6) Rain Barrels / Rain Water Harvesting – while rain barrels don’t filter pollutants, they help reduce water use and prevent flooding by storing rainwater on-site and slowing waterflow during high rainfall events. (photo credit: Green Infrastructure for Homeowners Manual, City & County of Honolulu, BWS)

7) Permeable Pavment (Porous Asphalt, Pervious Concrete, Turf Blocks, Permeable Paver Stones) – instead of paving a surface with solid asphalt or concrete, permeable pavement consists of either porous material, or solid material spaced apart to allow water to soak into the ground. This is especially suitable for parking lots, driveways, roadway shoulders, basketball courts etc. (photo credit: Green Infrastructure for Homeowners Manual, City & County of Honolulu, BWS)

8) Natural Green Infrastructure – forests, wetlands, natural streambanks and streambeds serve have the same as green infrastructure (and more). In many ways, green infrastructure seeks to mimic these natural features!

In 2016, the University of Hawaiʻi at Mānoa commissioned an initial feasibility assessment for an Infrastructure Master Plan which includes proposals for integrated wastewater and drainage systems to withstand a 100-year (1% chance) flood, offer flexibility for quick updates to support a 21st century campus, and achieve net zero water by 2050.

The Department of Facilities Maintenance, Storm Water Quality Branch provides information, resources, and tools on implementing Green Infrastructure, and features various green infrastructure projects in an interactive Atlas created by UH SeaGrant.

The Surfrider Foundation Oʻahu Chapter’s Ocean Friendly Gardens initiative helps create green infrastructure in Honolulu’s urban watershed – check out their map of Ocean Friendly Gardens!

The City of Honolulu runs a Storm Drain Markers volunteer program that supports groups to mark City drainage structures with the messages ‘No Dumping, Drains to Ocean’ at catch basins and ‘Unclutter Gutters, Litter Harms Our Ocean’ along curbs to raises awareness that our rainwater doesn’t get treated – it flows straight into the streams, the Ala Wai Canal and the ocean. Check out their video to learn more!

The preliminary designs of the US Army Corps of Engineers Ala Wai Canal Project include a number of grey infrastructure measures, such as retention dams and basins, and in-stream debris catchment features in Makiki, Pālolo, and Mānoa, a flood berm around the Ala Wai Golf Course, and a flood wall along parts of the Ala Wai Canal.

Sustainable Coastlines is a community non-profit that organizes large scale, hands-on beach cleanups, including the Ala Wai Canal, coordinates marine plastic pollution education programs, and works to implement solutions to catch floating debris through technologies like the SeaBin and Trash Water Wheel.

Current regulation by the City & County’s Department of Planning and Permitting require new buildings to have green infrastructure features capable of capturing a certain amount of rainwater on site.

The City & County’s Department of Facilities Maintenance (DFM) 2016 Stormwater Management Program Plan addresses a range of issues such as green infrastructure maintenance, outreach and education, best practices for construction site runoff, street sweeping, and others that fall in the City’s area of responsibility. Check out their video to learn more!

The AWWC’s Working Group on Policy, Finance, and Infrastructure helps coordinate to raise awareness of the importance of green infrastructure and its maintenance needs.

Cover photo credit: Punahou School Rain Garden, PBR Hawaii & Associates Inc.