Ka‘u residents are mostly in favor of a state Department of Transportation plan to raise Mamalahoa Highway by about 10 feet at Kawa Flats, according to the final environmental impact statement released this week.
Residents noted the difficulties caused by flooding of the highway by the flats in comments submitted for the document. The state DOT gave the project a finding of no significant impact.
The project will create a six-cell culvert that a consultant noted would function much like a bridge over the flood-prone area. Flooding has closed the road at least six times since 2002.
According to the State Transportation Improvements Program, the project is estimated to cost about $6 million. A department spokeswoman said department officials hope to advertise the project sometime between July and September 2013, with construction to start in March 2014.
In 2008, former Police Chief Lawrence Mahuna asked the DOT to expedite the project, because of the “current hazardous issues caused by the flooding.”
Construction will raise the highway surface about 10 feet, placing the road surface approximately two feet above the 50-year flood level, the assessment said. A reinforced concrete box culvert measuring 84 feet wide by 8 feet high would be placed beneath the highway. Each concrete cell will be 12 feet wide and eight feet high, the document said. The culvert would drain runoff directly from the north drainage basin located upstream of the culvert and be connected by a 260-foot long, 20-foot wide unlined channel to another drainage basin to the south.
“This culvert and channel would provide proper drainage capacity that would essentially maintain the current runoff patterns and flow depths but allows the runoff to pass under, rather than over, the highway,” the document said. “An additional smaller culvert would be placed under the highway south of the main culverts to maximize drainage efficiency.”
In all, the improvements would be placed along a 3,700-foot long section of the highway, which is more than 50 years old and has no drainage for the low-lying Kawa Flats section.
“Flood waters from an intermittent drainage frequently overtop the highway and completely close this round-the-island highway – the only route connecting the two main towns of Ka‘u,” the document said. “The flooding is a hazard to motorists, prevents the passage of emergency vehicles and damages the roadway.”
Construction should take about one year, the assessment said, and a temporary, paved, two-lane bypass mauka of the highway will allow drivers to avoid construction. DOT officials said they initially planned to build the bypass makai of the highway, but community comments and concerns about natural and historical resources prompted them to reconsider. DOT officials also ultimately rejected suggestions to use an existing, old plantation road mauka of the highway as a bypass, because the road lacks proper pavement, drainage, guard rails, sight distance and other safety features, and because it also floods during heavy rains.
The state will build an intersection near the northern end of the project to provide permanent access to the county’s Kawa property and access roads on the makai side of the highway, and to an old corral on the ranch land on the mauka side of the highway.
Last year, Area II Assistant Police Chief Paul Kealoha noted in his comments on the draft environmental assessment the ongoing dispute between Abel Lui, who is claiming a right to remain on county land at Kawa, and the county. Kealoha recommended DOT hire security guards and special duty police officers to provide site security.