Rain gardens protecting waterways

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WAIMEA — When it rains, gardens get much needed nourishment, but runoff from impervious surfaces sends pollutants such as heavy metals and oil into waterways and eventually into the ocean. Rain gardens are a way to prevent this from happening.


WAIMEA — When it rains, gardens get much needed nourishment, but runoff from impervious surfaces sends pollutants such as heavy metals and oil into waterways and eventually into the ocean. Rain gardens are a way to prevent this from happening.

Wai’ula’ula Stream, which begins in the Kohala Mountains and runs through the center of Waimea to the ocean, has been gifted one.

On Feb. 1, a rain garden was installed in the northeast corner of Waimea Center’s back lot. Led by Extension Agent Lisa Ferentinos from the University of Hawaii Sea Grant College Program (UHSGCP), student volunteers from The Kohala Center’s Ke Kumu Aina after-school program and Julia Rose from The Nature Conservancy and South Kohala Coastal Partnership (SKCP) assisted with its construction.

The garden is a shell-shaped slope made up of native Hawaiian plants such as ilima, mamaki, uhi uhi, mau hau hele, ti and ohia, to name a few.

“The idea is that the plants in the lowest part of the garden are adapted to being wetter. The ones in the upper part are adapted to being draught tolerant and the ones in the middle can handle a little bit of wet and a little bit of dry,” said Ferentinos.

The runoff is directed to the garden through a sub-surface pipe.

“The water comes in off the parking lot into this low area. There’s a pipe that helps distribute the water. You use the plants to bio-mediate any of the pollutants. The plants take up the water and anything that’s in the water, and any water that goes into the stream will be filtered,” she explained.

The rain garden project for Hawaii Island began back in 2014 through a conservation partnership.

“The South Kohala Coastal Partnership, of which UHSGCP is a member, helped find funding to do an assessment of Waiulaula Stream for the worse erosion hot spots. That was completed in 2014,” Ferentinos said.

Once five hot spots were identified, “They (SKCP) got funding from the Department of Health’s Polluted Runoff Control Program to address some of the worst erosion hot spots along Wai’ula’ula Stream,” she said.

Although there are many rain gardens on Oahu, Ferentinos has adapted the design of the Waimea garden to fit its specific conditions.

“This one might be the first on the Big Island. There’s quite a few on Oahu, but they’re at sea level and it’s a different situation, different soil, different plants,” she said.

The rain garden is one of many strategies to address runoff along the Wai’ula’ula Stream corridor. The first effort was to plant a strip of kikuyu for its low maintenance, and native hibiscus along the bank of the stream directly behind the center’s courtyard.

The next hot spot will be at the Ulu La’au Nature Park, where the Ke Kumu Aina program is centered. The group meets on Wednesdays from 1:30-5 p.m. to explore and learn about Hawaii Island’s native plants.

Ke Kumu Aina’s Program Coordinator Mahina Patterson and her students, who planted the rain garden, will be on hand to help.

“We will install erosion control matting, coconut fiber logs and vegetation to slow down the erosion of the banks. We already have a trial area to make sure that the concept we were considering was workable. We’re in the process of ordering the materials and getting the labor contracted to do that site, which we expect to happen in another couple of months,” said Ferentinos.

Ku’ulei Kumai-Ho from Waimea Middle School, Shaelynne Monell-Lagaret from Kanu o ka Aina and Julian Fried from HPA will lead the rain garden planting at Ulu La’au. But the care for the garden doesn’t stop there.

“In Hawaii there’s no such thing as no maintenance. That’s a huge challenge with all environmental projects here. We’re trying to get school groups to adopt areas that we’re doing our projects in. We’re trying to get teachers at Parker School and Waimea Middle School engaged. The idea is that each school or class can take on some part that matches up with their educational goals,” said Ferentinos.

The rain garden is both an experiment and a way to educate the community about how they can help prevent runoff.

“Once the plants are established, we’re going to have a workshop and invite the community to come and learn about rain gardens. We’re trying some techniques and plants that haven’t been tried before,” said Ferentinos.


The effort to prevent runoff is a whole community affair, and requires individual awareness of causes and how they can be fixed.

“We’re hoping to encourage folks to install rain gardens at their homes to deal with any runoff from their impervious surfaces like driveways or rooftops, and encourage other folks in the community to consider using rain gardens to have the excess infiltrate rather than runoff into the stream,” concluded Ferentions.

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