Fast-growing invasive plants are taking over Manoa’s shuttered Paradise Park, contributing to the stream bank erosion in the Ala Wai Watershed, which sends 995 tons of sediment annually to the Ala Wai Canal.

But the Ala Wai Watershed Association is on a mission to get to the root of the problem, literally. They’ve joined with Paradise Park’s owners, Warren and Napua Wong, and several organizations to remove invasives and plant native Hawaiian plants to shore up the crumbling banks at the two streams that wind through the site.

Thanks to volunteer labor and a $298,000 grant from the state Department of Health, they’ve removed large albizia trees from the site and cleared upper portions of stream banks of overhanging trees and debris that block volunteer access and provide too much shade for stabilizing plants to grow. They’ve installed rebar and erosion socks and are using native plants such as aeae and ahuawa to spread stabilizing root systems that shore up the Ala Wai Watershed, a 19-square-mile area that joins water bodies from the ridge of the Koolau Mountains to Malama Bay’s near-shore waters.

“If we all work together, I think we can make a huge difference,” said Karen Ah Mai, Ala Wai Watershed Association executive director, during a July instructional site visit to Paradise Park. “We’re increasing absorption capacity and reducing sediment and pollution. We’ve always said we need ecosystem restoration along with bridges, walkways and flood mitigation. We can’t solve all the problems for the conservation area, but at least we can start.”

Maryknoll School is the latest group to answer Ah Mai’s call.

“We wanted to find a service project where we could learn and make an impact,” said Maryknoll School President Martin Perry, who joined Ah Mai and more than a dozen volunteers on the recent site visit. “We see this as an important outdoor-classroom experience. We hope our students and their families will serve as trailblazers for the community.”

With 4,000 pohinahina plants expected to arrive for planting by September, Ah Mai said volunteers can’t come fast enough. More importantly, she’s also on a hunt to recruit more people to learn conservation skills and spread them throughout the community.

Ah Mai said the association is working with partners like the Oahu Resource Conservation & Development Council, the Hawaii Association of Conservation Districts, and the Natural Resource Conservation Services to pilot national conservation standards that could be applied to problem areas throughout the Ala Wai Watershed.

Since the upper watershed is connected to the lower waters, efforts like these are critical to managing sediment and restoring the Ala Wai Canal, said Dolan Eversole, who serves as Waikiki Beach management coordinator through the University of Hawaii Sea Grant College Program.

“The Ala Wai Canal is meant to be 6 to 10 feet deep, but sediment has reduced parts of it to only 2 feet deep,” said Eversole, who joined volunteers on the Saturday site visit. “As the canal fills in, it doesn’t have the capacity to hold storm water. As the sediment washes out of the canal, it can impact the coastal near waters.”

Risk experts have warned state lawmakers that continuing the Ala Wai Watershed’s vulnerability could result in financial devastation. If a Category 4 hurricane hit Oahu, some estimate damage to Waikiki alone could hit $30 billion, in part because of the watershed’s current state. A 100-year flood in the watershed could cost an estimated $318 million in damage. Even heavy rain can cause major sewage spills that shut down Waikiki beaches, contributing to the canal’s reputation as one of the nation’s most heavily polluted water bodies.

“It’s so cool to be up here in the mountains helping out the coral reef,” said Judy Bowman, who volunteers with Ah Mai’s crew. “Right now, I’m clearing out elephant ear plants. It’s hard work, but it’s worth it to know that I am doing something important for the environment.”

For information about volunteering, contact the Ala Wai Watershed Association at alawaiwatershed@gmail.com.