The Honolulu City Council on Wednesday voted by a narrow 5-3 margin to approve a measure allowing Mayor Kirk Caldwell to move forward with the contentious $345 million Ala Wai flood mitigation project.

The project being spearheaded by the U.S. Army Corps of Engineers is supposed to protect the areas around the Ala Wai Canal — and Waikiki specifically — from heavy flooding during a large-scale storm by building a series of detention basins along the Ala Wai watershed including Manoa, Palolo and Makiki, as well as walls on the sides of the canal.

But a slew of residents from Makiki to Kapahulu raised concerns that the project may increase the likelihood of flood damage in communities upstream from Waikiki.

Caldwell and other city officials warned that failure to pass Resolution 19-182 by Aug. 31 could jeopardize the $245 million federal share of the project.

Gov. David Ige has agreed, in principle, to use state funds to pay the “non-federal” $125 million share of the project, despite the Legislature’s decision last session to reject funding for it.

Caldwell, in an unscheduled appearance before the Council Executive Matters and Legal Affairs Committee prior to a preliminary vote, said he will meet with Ige today to get assurances about the funding.

Several Council members said they are worried that the city would be stuck with paying the full $125 million if the state does not provide its share.

Caldwell called that scenario highly improbable since it would adversely affect the state’s bond rating.

Members Carol Fukunaga, Kymberly Pine and Heidi Tsuneyoshi voted “no.” Council Chairman Ikaika Anderson was joined by Brandon Elefante, Joey Manahan, Ron Menor and Tommy Waters in voting “yes.” Councilwoman Ann Kobayashi, who was excused from the meeting, had earlier indicated she would likely vote “no.”

Palolo resident Dave Watase, who was told his property may have to be condemned to complete the project, said designers have failed to look seriously at a better and cheaper solution: a flood gate at the Ala Wai Boulevard Bridge. He said the flood gate would be fed by high capacity flood pumps that would drain the canal, similar to what’s been done in New Orleans.

“No detention basins and no wall,” Watase said. “No ugly walls, no blocking of views, no destruction of streams in the upper watersheds.”

Winston Welch, executive director of the Outdoor Circle, said the Council had held only one committee meeting “on one of the largest public works projects this century.” He urged Council members to delay approval and seek a more comprehensive solution.

Welch said what he’s seen so far is a poorly planned project that’s “a rushed, hurried project with misinformation, disinformation (and) lack of information.”

Sidney Lynch, who said she lives downstream from one of the basins, is worried that poor maintenance will result in the basin failing during a storm. “Fear of failure is legitimate when these dams are 33-feet tall,” Lynch said.

Not everyone opposed the project. Waikiki Neighborhood Board member Kathryn Henski said the canal was created to make way for commercial development of Waikiki. She and 25,000 other residents there are seeking protection through the mitigation project.

Oftentimes, people think of the area as just about hotels and resorts “when, in fact, we’re neighborhoods,” Henski said.

Menor, chairman of the Executive Matters panel, said a committee report on the resolution calls for federal engineers to take into consideration the concerns of residents.

Pine said the state funding should be secured and a final environmental impact statement completed before the project moves forward. “Seems like we’re doing things backwards.”

Both Jeff Herzog, the corps’ Ala Wai Flood Risk Management Project manager, and city Design and Construction Director Robert Kroning assured the Council and the public that there will be ample time for community input.

Herzog, who acknowledged that the project must be modified to achieve its objectives, said his team already has been studying the suggestions made by the community and incorporating them into their plan.

“The resolution just allows us to accept the limited funds,” Kroning said. “It allows us to take the next step forward.”