The Ala Wai Canal was constructed more than nine decades ago as a means to drain Waikiki marshlands to allow development. Now, the state’s top tourism magnet faces threats along mauka and makai boundaries that could bring waters seeping or pouring back into the hotel-lined beachfront district.

Threats on either side are linked to climate-change uncertainties. On the makai side is a sea-level rise projection of 3.2 feet over the next 30 to 70 years. On the mauka side, due to the Ala Wai watershed’s sheer slope and considerable annual rainfall, the canal is designated at “high risk” of flash flooding.

Congress has approved a $345 million Army Corps of Engineers project to fortify the canal and upstream areas. But the release of some $220 million in federal funds hinges on signing an agreement at state and city levels for the money balance, and that is giving rise to some concerning unanswered questions.

Last week, despite opposition from several neighborhood boards in areas slated for mitigation construction, the City Council voted by a narrow margin to approve a resolution allowing Mayor Kirk Caldwell to move forward on the project.

At the state level, legislators rejected a bill to allocate $125 million for the project, saying it was a city issue. Gov. David Ige, though, has moved forward with a “certification of participation” — backed by investors, similar to bonds — that requires no legislative approval.

Prodding the hurried push forward is an ostensible Aug. 31 deadline to seal the deal or risk losing the federal dollars. But given the concerns, our local governments should seek a deadline extension, time needed to sort out the best path forward.

The project calls for installation of in-stream detention basins in the upper reaches of Makiki, Manoa and Palolo. The basins would cross into some properties along the watershed, including residential land as well as private and public school boundaries. On the Waikiki end, 4-foot-high concrete floodwalls would go up along the Ala Wai Canal.

Under the current plan, local government is tasked with paying for 35% of construction, while federal government covers the 65% balance. The city envisions its role as spared from pitching in for construction, but on the hook for maintaining the upgrades.

While a project design study, now 35% complete, remains open to minor tweaks, major adjustments are apparently off-the-table — short of approval in federal circles.

Community members are rightfully concerned of a plan that locks in engineering strategy prematurely. While it might stop flood waters from topping the canal, could it create undue upstream threats and maintenance headaches in residential neighborhoods? City maintenance of storm drains and culverts has been known to be spotty.

Options such as tech-focused innovation supporting habitat restoration and re-purposing city- or state-owned land, need more vetting in public forums.

Upstream, 15 years ago, an October storm that flooded Manoa Valley caused upwards of $70 million in damage to state property. Since then, improvements such as dredging to create deeper stream bed areas have helped ease the threat. Such mitigation measures need fuller examination.

Canal overflow severe enough to require more than $1 billion in Waikiki repairs is pegged as a 100-year event, meaning a 1% probability of it occurring in any given year. Despite the long odds, such a scenario must be addressed proactively, given the outlook for more intense storms tied to climate change.

In addition to seeking more time to weigh options, with the goal of collective community consensus, the city and state should forge ahead together. Given tourism’s role as Hawaii’s economic driver, even a slim potential for massive flooding in Waikiki is a statewide problem.