Congress has appropriated $345 million for a major revamp of the Ala Wai Canal and the watersheds flowing into it, a project federal engineers say is needed to keep a massive flood from wiping out Waikiki.

“It’s only a matter of time that we get a really big event,” said Michael Wyatt, chief of the civil and public works branch at the U.S. Army Corps of Engineers in Honolulu. “It basically could put Waikiki completely underwater.”

The U.S. Army Corps of Engineers estimates the disaster would damage 3,000 structures and cost more than $1 billion in repairs. The new federal money is enough to cover the entire cost of fortifying the canal and the watersheds that feed into it to minimize damage from the inevitable flood.

“This is really unusual for us,” Wyatt said. “What we expected to get with Ala Wai was an appropriation every year. In this case they basically appropriated everything all at once.”

Ala Wai Canal brown water after Darby. 25 july 2016
A 100-year flood would cause the Ala Wai Canal to overflow and put Waikiki underwater. This photo shows the canal stained with brown water after tropical storm Darby in July 2016. Cory Lum/Civil Beat/2016

The money was part of the 2018 supplemental budget approved in February. The Army Corps announced the specific projects that would benefit from the funding on July 5.

“We were pleasantly surprised that we actually got everything that we requested and that’s very rare,” said U.S. Rep. Colleen Hanabusa, who testified before the Corps of Engineers last year to urge the agency to prioritize the project. She along with the Hawaii delegation advocated for the funding in Congress.

“They recognized that what is at stake is not merely one watershed area or one canal,” Hanabusa said. “What is at stake is the economic engine of Hawaii, which is Waikiki.”

The city or the state — or both — will have to bear or share one-third of the total project cost, about $115 million, Wyatt said. It’s still unclear who will pay how much and how or when the federal government will be repaid.

Gov. David Ige and Honolulu Mayor Kirk Caldwell sent a letter to the Corps of Engineers in 2016 expressing support for the project. They suggested they might enter into a private-public partnership to cover the local share of the project.

Suzanne Case, head of the state Department of Land and Natural Resources, said the details will be worked out after the state and city receive more guidance from the Corps.

“Now we start a process of detailed discussions between the administration, city and county and ultimately the Legislature on co-sponsorship responsibilities for this project and funding,” Case said Monday.

Watch this video from the U.S. Army Corps of Engineers to learn about the flood risk to Waikiki and why it matters.

The project consists of developing detention areas along the Makiki, Manoa and Palolo watersheds to catch water, debris and sediment before it flows downstream. This includes multiple earthen structures to manage stream flows and a concrete pad in the Manoa stream to catch debris. The Ala Wai Golf Course would function as a detention basin as well once engineers install berms along the north and east perimeter.

Another key component involves building concrete floodwalls along the canal to catch rising water. The walls would average 4 feet high, with some less than a foot high and others as tall as 6 feet depending on the slope, Wyatt said.

Carty Chang, chief engineer at the Department of Land and Natural Resources, said residents will get a chance to weigh in on the project as it moves through the permitting process and officials conduct historic preservation reviews.

Case said the state asked the Corps of Engineers to look into ecosystem restoration for the watershed in the 1990s. The focus of the project shifted to flood control after a 2004 flood in Manoa caused $85 million worth in damage and heavy rainfall in 2006 flooded the neighborhoods of Maikiki and Moiliili.

“That wasn’t even close to a 100-year storm,” Chang said of the Manoa flood. “That was a 25-year storm.”

The U.S. Army Corps of Engineers’ rendering of the impact of the 100-year flood on Waikiki. 

Hanabusa noted that the recent destructive flooding in Kauai underscored the importance of preparing for a similar disaster in Waikiki. “We lost homes, we lost loi,” she said, referring to taro farms. The flooding of Waikiki would risk many more homes and businesses.

Even if the project moves forward smoothly, Wyatt said it may take two years to design the project and another four years to build it.

“There are a lot of folks who questioned whether or not this would ever happen,” Wyatt said. “It’s good news for the project but what it all really means — unfortunately we don’t have all the details at this point in time.”

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