Alii Drive bridge and culvert to be replaced at Kahului Bay

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HILO — For almost 80 years, motorists and pedestrians have traversed the Alii Drive bridge at Kahului Bay.

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HILO — For almost 80 years, motorists and pedestrians have traversed the Alii Drive bridge at Kahului Bay.

Time has taken its toll on the bridge, which was not designed for the traffic load of today. The concrete is crumbling and the county has installed braces underneath the bridge to keep it propped up until it can be replaced.

That time is now, the county says. Not only must the bridge be replaced for structural reasons, the underlying culvert needs to be expanded and the drainage channel needs to be widened to accommodate a 100-year flood and to restore a more natural circulation in the bay.

Hawaii County has issued a finding of no significant impact for the work, according to a report issued Saturday. The public can comment on the project until May 8.

The project, to be paid with federal funds, is estimated to cost about $12 million and take about a year to complete. Work is expected to start in February, but may not begin until February 2019, depending on the availability of funds, said Ron Terry, with Geometrician Associates.

“The bridge will be open to two lanes of traffic at all times,” Terry said. “We don’t think Alii Drive can handle even one lane of traffic being closed.”

Keeping the road open to traffic will obviously slow the construction time, he acknowledged. It will also slow the already snail’s pace of traffic on the road.

“It’s got to get replaced,” Terry added. “It’s really dilapidated.”

The widened bridge will accommodate bike lanes and raised sidewalks.

The drainage channel will be widened for a distance of 100 feet upstream of the new culvert structure in order to ensure that the 100-year flood is contained within the embankments. This widening approximates the channel’s natural width prior to its narrowing in the 1930s when the culvert structure was built, the report states.

The new structure will consist of a single span concrete bridge with a length of 70 feet and a width of 49 feet. The vertical clearance beneath the bridge will vary from 8 feet at the downstream end to 9 feet at the upstream end of the bridge.

The channel bottom will remain unhardened and will consist of naturally occurring boulders and cobbles, which will assist in reducing flow velocity at the ocean outlet. The embankments will be protected from erosion with grouted rubble paving, according to the report.

Because of the narrow openings and small cross-sectional area, the stream embankments are often over-topped by the flood waters that inundate the adjacent private properties, the report states. The flood waters sheet flow across Alii Drive during heavy flooding.

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A pdf of the full, 356-page report can be found at http://oeqc.doh.hawaii.gov/Shared%20Documents/EA_and_EIS_Online_Library/Hawaii/2010s/2017-04-08-HA-5B-DEA-Alii-Drive-Culvert-Replacement.pdf (Note: 50 mg file may take some time to download).

Comments can be sent to Department of Public Works, attention Casey Yanagihara, Casey.Yanagihara@hawaiicounty.gov or 101 Pauahi St, #7, Hilo, HI 96720, with copies to consultant Geometrician Associates, attention Ron Terry, rterry@hawaii.rr.com P.O. Box 396, Hilo, HI 96721.