It’s looking more likely that flood-protection plans for the Ala Wai Canal will include walls or raised barriers to flooding, an option that has been the subject of hot debate.
For safety’s sake, flood barriers as an element of an Ala Wai project can be justified. For Honolulu’s sake, however, any project running through this central artery dividing Waikiki from the rest of the city must be designed with care, so that the Ala Wai corridor is an attractive, pedestrian- and community-friendly asset.
Whatever is built along the Ala Wai will be something Honolulu residents must live with for decades, and it’s the city’s responsibility to do it right. The Ala Wai flood control project must be integrated with a vision for the corridor that prioritizes the experience of those who use it — or would, if it wasn’t the often-stinky, bacteria-tainted and ugly concrete channel that it is today.
Any berms or flood barriers should be designed to create an attractive, landscaped promenade for community members and visitors alike. And aside from flood control, the canal waters present a safety issue, with contaminated sludge and high bacteria counts; that too must be remedied.
The city will reveal its “Tentatively Selected Plan” for flood control in May or June. Its challenge is to protect without creating, or perpetuating, a monstrosity.
The latest options, presented by the U.S. Army Corps of Engineers and the city last week, have been selected after years of analysis. Along the way, a highly engineered, $650 million plan was scrapped, and the city obtained federal funding to study greener, less expensive options.
At issue, balancing cost and interventions, is the level of flood protection. The Corps considered potential rainfall levels ranging from what’s experienced most years, at 50% to 100% probability, on up to a disastrous 500-year storm, a 0.2% risk in any given year.
Planners have narrowed the options to four. One is doing nothing. That’s unwise, as it would expose Waikiki and neighboring communities to major damage from flooding.
Another option emphasizes “water storage,” with retention basins along the watershed, including at Makiki District Park, Manoa Valley District Park and the Ala Wai Golf Course, designed to hold excess stormwater before it could flood the Ala Wai. This option does not include higher walls or berms along the Ala Wai; however, it only protects against a 20-year storm, creating vulnerability if a stronger storm hits.
One option bypasses water retention in favor of “water conveyance,” or channeling water into a walled-up Ala Wai, with barriers to flooding along the way.
What appears to be the best option blends strategies, with retention basins in Manoa and at the Ala Wai Golf Course as well as 6-foot-high flood barriers along the canal. This would protect against flooding in the case of a 50-year storm — a storm that Honolulu faces a 2% risk of experiencing each year — and because this is more protective, it would seem the preferred choice.
There is room for unease over whether even this option is sufficient. City planners and residents could potentially sleep more easily if the plan protected against a 100-year event, or worse, because many scientists believe storms will become more severe and unpredictable in the coming decades as Earth’s atmosphere warms.
Protections must be added, because flooding along the Ala Wai could cause damage that far surpasses the cost of flood control, and failing to truly improve the Ala Wai should not be an option.
Haku Milles, city Department of Design and Construction deputy director, last week said that the city is “absolutely committed” to making flood walls “anything but plain concrete.” That commitment must be backed up with an overall design that makes a stroll beside the canal far more attractive than it is today.
