The Ala Wai Canal is a disaster waiting to happen — a channel for drainage that can’t hold enough water to protect Waikiki from a 100-year flood event, or worse. Sea level rise connected to global warming raises the threat level higher.

It’s also a disaster that has already happened — a smelly, polluted stretch of water that is contaminated with flesh-eating bacteria, toxic runoff, garbage and sludge, despite recent dredging and ongoing cleanup efforts.

To protect Waikiki from flooding, the Ala Wai Canal needs fixing, along with the drainage systems feeding it. Honolulu is in the public comment stage of planning this, in concert with the Army Corps of Engineers. We call on all concerned to forge a coordinated solution that prioritizes green remedies, constructing not only holding tanks and channels, but also a more resilient ecosystem, and a cleaner, more attractive and more widely usable Ala Wai Canal.

The city and state have been working with the Army Corps of Engineers on a flood control system for the Ala Wai watershed since at least 2017. The first solution proposed by the Corps included walled retaining ponds high in the watershed, raised concrete walls along the canal itself and a four-story-high pumping station, at a cost that ballooned to more than $650 million.

Facing the expense and intense pushback from residents along the project’s path, the project was scrapped, and the city and Corps began planning anew.

This time around, the Corps is examining other, less intrusive and more cost-effective ways to retain water in the highlands and throughout the watershed, which includes Manoa, Palolo and Kaimuki.

The new study has expanded to consider flooding that could occur within a range of five to 500 years — a wise decision as the project will be expensive work, and Honolulu won’t want to redo it in the foreseeable future.

Matthew Gonser, executive director of Honolulu’s Office of Climate Change, Sustainability and Resiliency, is a city point person on projects related to sea level rise, flooding and environmental restoration. We’ll be looking to him, along with other city and state departments with oversight, to guide this project toward clean-and-green results.

It’s imperative that the city keep community use and environmental health at the forefront, as the Corps has more limited concerns.

Last year, in an interview with the University of Hawaii’s Sea Grant program, Gonser raised the concept of “One Water,” which would share resources for Honolulu’s oversight of wastewater, drinking water and stormwater to encourage conservation and reuse. In light of Honolulu’s water crisis at Red Hill, this kind of shared responsibility is a must.

Note that open land in the watershed is likely to play a vital role in this project. Holding water at Ala Wai Golf Course, already vulnerable to flooding from rising seas due to global warming, is a first-tier option. At Ala Wai Community Park, possibilities include diversion ponds at the ball fields and engineered wetlands. At Kanewai Community Park, underground water storage is under consideration.

Upstream, restoration work to remove invasive plants and restore vegetation that can help to hold stormwater is being supported with a $1.6 million grant from the National Fish and Wildlife Foundation. This kind of environmentally sensitive work should be a key part of the solution, reducing runoff and keeping water that flows downstream cleaner.

Flood control work in the Ala Wai watershed provides a once-in-a-lifetime opportunity to preserve clean water, improve the ecosystem and maximize community access to the waterway. Let’s do this right.