Ala Wai plan to address flood threat, ecosystems

By James Gonser
Advertiser Urban Honolulu Writer

A new federal-state project in the Ala Wai watershed to reduce the high potential for major flooding could cost $60 million and take up to a decade to complete.

Among the options being considered are constructing flood walls around the Ala Wai Canal, widening the canal and modifying bridges.

The Ala Wai watershed covers the most congested urban area in the state, and is home to more than 161,000 people. The watershed's streams, springs and pools flow from an abundance of rain from the Ko'olau mountains, and rainstorms often send debris and runoff into the Ala Wai Canal.

With parts of streams covered in concrete, and pollutants from cars and pesticides in the water and the canal, the watershed desperately needs improvement, said Karen Ah Mai, executive director of the Ala Wai Watershed Association.

"The water quality is really bad," Ah Mai said. "It hurts the people that use the canal because they get some bad infections if they get a scratch or a cut and the canal water gets in. It's a real health and safety issue. The water is so bad, if it goes over the banks, it will be a tremendous health problem."

Urban impact

Though other areas have experienced worse flooding in recent years, the Ala Wai Canal, at its current capacity, has been found to have only marginal ability to handle a 10-year flood event and definitely could not handle a 100-year flood, according to the initial project report.

And increasing urbanization promises further degradation.

"As saturated as the area is, it's still going to continue to grow," said Derek Chow, with the U.S. Army Corps of Engineers. "Whether it's changing single-family dwellings into multi-family dwellings, people are going to make alterations in this watershed and it is being impacted by all this urbanization. If we can mitigate that, slow it down if not abate it, we are going to protect our environment and hopefully reverse some of that degradation."

The Army Corps and the state Department of Land and Natural Resources are working together on the project, which, if approved by Congress, would use 65 percent federal money and the remainder from the state.

Chow said the waters of the Ala Wai Watershed have suffered from significant environmental degradation, including heavy sedimentation, poor water quality, lack of habitat for native species and a prevalence of alien species.

Potential for damage

In the event of a 100-year storm, there is high potential for flood damage to the densely populated and economically important areas of Waikiki, McCully and Mo'ili'ili, Chow said.

"The purpose of the meeting is for us to give those that attend an idea about what the project entails," Chow said. "What kind of things we are looking at and to gain information from the public about what they think are impacts we should be considering."

The other options being considered in the lower portions of the watershed include dredging the canal and diverting flood waters through the Ala Wai Golf Course.

Ecosystem restoration actions being investigated include stream channel reconstruction, stream bank revegetation and reinforcement, sedimentation basin and dam construction, debris catchment and energy dissipation, and better maintenance accessibility.

"We are looking to restore the habitat, not take it back to the condition as it was 100 years ago," said Andrew Monden, with the DLNR. "This is the beginning of the planning process where we present concepts to the public. Based on their comments we can move ahead with the draft environmental impact statement."

Reach James Gonser at jgonser@honoluluadvertiser.com or 535-2431.