Alii Drive culvert replacement project expected to start in February 2019

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The wall adjacent to the double-cell culvert bridging the Waiaha Drainageway on Alii Drive shows signs of erosion. (Laura Ruminski/West Hawaii Today)
The double-cell culvert bridging the Waiaha Drainageway on Alii Drive. County officials say work to replace the structure could commence in February 2019. (Laura Ruminski/West Hawaii Today)

KAILUA-KONA — Work to replace a rapidly deteriorating culvert on Alii Drive is expected to get underway early next year.

Department of Public Works spokesman Barett Otani said the county expects the project to go out to bid by November or December of this year, so long as all of the necessary permits are obtained and plans are approved. If all goes smoothly, work to change out the more than 80-year-old culvert on the Waiaha Drainageway near Kona Tiki Hotel could get underway in February 2019.

Work is expected to last approximately one year.

Despite the bridge being described as “structurally deficient” and “functionally obsolete” and near the end of its design life, Otani said “Our bridge engineers have deemed it safe for use.”

The project’s anticipated cost is about $12 million; 80 percent of which will be funded by the Federal Highways Administration. The county has already allocated its $2 million toward the work and the feds have contributed $9.66 million.

Phased construction would minimize impacts on traffic and pedestrians. The county says it will keep two lanes of traffic open at all times and install a temporary pedestrian path and bridge.

The culvert, also referred to as a bridge, was built in 1937 and is located about 1.5 miles south of the center of Kailua Village. It is classified as both “structurally deficient” and “functionally obsolete.” Structurally deficient means the bridge has a significant defect that often means that speed or weight limits must be put on the bridge to ensure safety. The current speed limit over the culvert is 25 mph.

The county has reinforced the culvert, most recently after flooding in September 2015 with 12-by-12-inch wooden posts, but it needs to be replaced after preliminary design work determined it cannot cope with repairs, maintenance and upgrades.

A final Environmental Assessment released last summer for the project stated several times, using varying wordage, that the culvert could deteriorate to the point the road becomes unusable.

“If not repaired, it may soon require closure, cutting a critical link on Alii Drive that would cause traffic detours of up to two miles and lead to severe traffic and socioeconomic disruption,” the document’s opening project summary reads.

When prompted about concerns of the culvert collapsing, as occurred in Paauilo amid inclement weather in 2013, Otani said the county has a program in place that inspects biannually all of its 129 in-service bridges listed on the National Bridge Inventory.

“The county’s primary focus is public safety and is always concerned for the safety and integrity of Hawaii Island’s bridges. However, it is difficult to predict the severity of weather events that may jeopardize bridge structures,” Otani said via email.

The new $12 million structure would include a wider and longer culvert structure capable of handling more water flow with a longer, wider bridge above featuring bike lanes and raised sidewalks.

The drainage channel would be widened 134 feet upstream, with a natural bottom of sand and cobbles. The longer span would permit the culvert openings to allow a 100-year design flood to pass through, and approximate the channel’s natural width prior to its narrowing in the 1930s. The fix is needed because the embankments are often over-topped by flood waters that inundate the adjacent private properties and Alii Drive.

The county had worked to address the culvert in 1998, but the project was put on hold because of financial constrictions. Current efforts to replace it started around 2014.