The U.S. Army Corps of Engineers estimates that a major flood in the Ala Wai Watershed could damage thousands of buildings in Waikiki, mostly, and require more than $1.14 billion in repairs. The chances of seeing this worst-case-scenario materialize is gauged as a 100-year event, meaning a 1% probability of it occurring in any given year.

That adds up to a slim chance. Still, given the frequency of storms here — anchored by the annual six-month hurricane season — and threats of increasingly intense bouts of bad weather tied to climate change, there’s little doubt that more can be done to reduce risk of disastrous flooding.

However, there’s also a risk linked to inflicting potentially irreversible damage to the watershed, if mitigation is mapped out in the absence of an approved Environmental Impact Statement (EIS). Such an EIS needs to thoroughly assesses development or activity impacts on land and water flow as well as historical, archaeological, cultural and social effects.

In the case of the proposed $345 million Ala Wai Canal Flood Risk Management Project, both the city and state have yet to sign off on an EIS document. That rightly prompted a senior Environmental Court judge this week to rule that the state cannot commit state funds to the project before an EIS is accepted.

Given the long-term aim of balancing public interests, the ruling brings a welcome tapping of brakes for the project, which has been pushed forward at city and state levels to meet funding deadlines.

While Congress has approved the project, release of some $220 million in federal funds has so far hinged on securing a memorandum of agreement committing the state to pay the project’s balance money, $125 million, by late November while the city agrees to maintain the completed project.

In recent months, Gov. David Ige and Mayor Kirk Caldwell signed off on the agreement — despite a clamor for more public engagement, fueled by worry that the deal could lock in plans for structural elements ranging from large upstream detention basins to flood-control features along the canal, including a 3- to 5-foot-tall wall.

The city’s forward motion was opposed by seven out of eight neighborhood boards — Waikiki’s the exception — in areas slated for construction. Contending that the project lacks the necessary EIS approval, Protect Our Ala Wai Watersheds, a recently formed community group, filed the lawsuit that resulted in this week’s court injunction that halts state funding.

Also, in recent months, mounting opposition prompted additional Corps of Engineers study aimed at upstream changes that could be less intrusive while still effective in addressing flood hazards. And, responding to complaints that a canal wall would be an eyesore, the Corps is now recommending earthen berms, which likely will be more palatable for both residents and tourists. With that change, and the possibility of others, the EIS is in need of an update.

The project’s environmental-impact snag conjures Superferry memories, which serve as a sort of cautionary tale.

Back in 2005, in apparent eagerness to see the Superferry launched — after contributing about $40 million in harbor improvements — the state exempted the project from some environmental review requirements, including an EIS. But days after the ferry’s debut in 2007, the Hawaii Supreme Court ruled the state should have required an EIS and other reviews.

Subsequent EIS-related stops and starts eventually forced the Superferry to halt operations, and the company entered bankruptcy in 2009.

In the case of the Ala Wai project, consequences of the Environmental Court ruling remain unclear. But what should be clear to all involved in big-impact projects is that there’s no cutting corners for environmental requirements.