Army Announces Modified Plan For Ala Wai Flood Project

Aug 19, 2020

The U.S. Army Corps of Engineers has released a revised plan for the controversial Ala Wai Flood Control Project, following public opposition to the original proposal.

The Ala Wai Watershed stretches from Palolo to Makiki. Any drop of water that falls within that area will eventually drain into the Ala Wai Canal and flow out to sea.

The heavily paved and developed neighborhoods, both mauka and makai, no longer allow for the absorption of high volumes of water during heavy rain events, such as those seen in 2018 in Aina Haiana. That has created a substantial flood risk for low-lying neighborhoods such as Waikiki, Moilili, and McCully.

The Army Corps of Engineers, which has regulatory oversight of all inland waterways in the United States, wanted to reduce the risk posed from a rain flooding event.

In 2017, Congress approved funding for a massive project to raise the height of walls along the canal and create a series of detention basins in the upper watershed. The stated goal of the project was to movement of surging storm runoff as it descended from the upper watershed to the lower, thereby giving time for outflows, and ultimately the canal itself, to drain without overflowing.

Major rain events, sometimes referred to as “rain bombs,” are expected to become increasingly common. Fueled by climate change, a warmer atmosphere can hold more water in vapor form.

Local leaders, particularly Honolulu Mayor Kirk Caldwell, have said publicly that adapting to a changing climate will require massive investments to harden highly developed areas in the urban core of Oahu. The Ala Wai Flood Control Project was billed by the federal government as an early example of climate adaptation.

Despite that pitch, residents in the area came out against the project. Many called the plan invasive and destructive,  viewing their neighborhoods as being put at risk to save Waikiki. In particular, residents of the upper watershed expressed concern about the plan to build six retention basins throughout Makiki, Palolo, and Manoa. Those would be used to collect and temporarily hold storm water, but generated fears of creating a new flood risk upslope.

After much, high-profile pushback in the community, including from several members of the Honolulu City Council, the Corps announced last September that it would go back to the drawing board and redo the design.

Under the revised proposal released this week, the controversial neighborhood detention basins have been replaced by catchments in parks and the Ala Wai golf course. That was an alternative often suggested during public testimony.

The Corps of Engineers says the new plan incorporates community feedback and addresses concerns about upstream detention of flood water. But opponents of the project remain skeptical.

A map depicting planned features for the Ala Wai Flood Control Project, including features that have now been dropped from the project.
Credit U.S. Ary Corps of Engineers Honolulu District

In response to the revisions, the group Protect Our Ala Wai Watersheds, a leader of the opposition, acknowledged that public concerns over the detention basis had been incorporated, but  argued other ideas to make the project more environmentally friendly had been ignored.

In an email, the group’s President Sidney Lynch called the new plan cobbled together and said that the redesign effort was hamstrung because funding had already been approved for the original design.

Officials with the state, City and County of Honolulu, and the Corps of Engineers have all expressed support for the project and argued that failure to adopt the original plan could jeopardize the more than $200 million in federal funds already earmarked.

Lynch specifically noted that recommendations developed by Oahu-based design firm Oceanit, which was commissioned by three members of the City Council to develop an alternative to the Corps’ plan, were not included. The Oceanit plan called for use of subsurface drainage tunnels, which it calls Subsurface Watershed Inundation Flow Technology or SWIFT, to bypass the Ala Wai Canal and move water out of the watershed.

The Corps of Engineers says a public meeting is being planned for later this year to present the design to community and solicit feedback.