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If you thought Tropical Storm Darby was bad, just wait. The U.S. Army Corps of Engineers has been warning Hawaii residents of a massive flood likely to hit the islands within a century.

The so-called 100-year flood could overflow the Ala Wai Canal, swamping Waikiki and causing hundreds of millions of dollars in damage.

The Honolulu office of the U.S. Army Corps of Engineers is finalizing a plan to set up berms and build 4-foot walls along the canal to mitigate the potential flood damage.

The final report won’t be ready until Aug. 24, but project manager Derek Chow said it will likely include more walls along the Ala Wai Canal despite some public criticism of the aesthetic impact of building them.

Chow said local U.S. Army Corps of Engineers officials will travel to Washington, D.C., in October to defend the plan before the assistant secretary of the Army for civil works. If the proposal is accepted, a record of decision may be issued in January.

It will be another few years before construction could begin, however. Congress would need to set aside at least $113 million, assuming the project cost remains $175 million.

State and city officials would need to come up with at least $61 million as well. Chow said that might require public-private partnerships.

It would also require public support. The U.S. Army Corps of Engineers received over 70 public comments, and several commenters opposed building a wall along the Ala Wai Canal, saying it would ruin the canal’s historic value.

But Chow thinks there’s no viable alternative. In fact, the latest version of the plan may even extend the wall to take into account concerns from Iolani School about potential flooding.

Chow said one benefit of storms like Darby is that it serves as a reminder of the need for flood mitigation.

“When it’s nice and sunny… it’s easy to forget,” he said.

Click here to learn more about the plan.

For more about the huge flood that could swamp the Ala Wai Canal, click here.