The state Department of Transportation has completed a draft environmental assessment for a nearly $3.2 million project to protect the shoreline and Kahului Beach Road from eroding into the ocean.
Plans call for building a 1,730-foot-long rock revetment parallel to the road from its intersection with Kaihee Place to the rock wall supporting the base of Kahului Harbor's west jetty, according to a project description published last week in the state Office of Environmental Quality Control's issue of "The Environmental Notice."
Project planners considered eight alternatives, including one of "no action." Doing nothing would mean that erosion would continue to occur, "and eventually undermine the highway until it becomes a safety hazard for motorists and pedestrians.
A food truck (left) and a pickup truck are parked within feet of an eroded area Friday at Kahului Harbor. The state Department of Transportation plans to build a nearly $3.2 million rock revetment to protect the shoreline and prevent surf from washing away a portion of Kahului Beach Road.
The Maui News / MATTHEW THAYER photo
"At that point, because in some areas the road is located in close proximity to the ocean, sinkholes or large sections of the road could break off into the ocean. During storms, the waves would continue to surge onto the highway causing road closures and debris dispersion," the draft environmental assessment says.
Of the other alternatives, the most expensive considered was a nearly $4.1 million revetment with tribar armors. This shoreline protection structure, widely used in American Samoa and other Pacific islands, is an efficient design using three concrete-formed cylinders connected at the center with concrete branches. The tribars interlock with each other and are effective in dissipating wave energy, according to the assessment.
The least expensive action alternative, estimated to cost $1.6 million, would entail building five 110-foot-long groins, or low walls, perpendicular to the shoreline and spaced 340 feet apart along 1,700 feet of the shoreline.
The alternatives were evaluated using a weighted system, and the rock revetment option was chosen as the preferred alternative. It scored highest among the alternatives for erosion protection and was in the middle for total cost.
"This alternative provides erosion protection, has a moderate cost, can be easily constructed, has a low impact on the harbor and has a low impact on the environment," the assessment says.
The alternative "offers a solution that will protect the integrity of the shoreline and the adjacent Kahului Beach Road. Rock revetment is extremely durable and can last more than 50 years. The rock revetment will initially need maintenance as the rocks begin to settle, then periodically rocks may need to be added or moved if they become displaced by wave action . . . (It) will blend well with the existing environment while still providing access to the shoreline."
The least expensive alternative, the low-wall groins, rated best for cost but lowest for shoreline protection. It also would have the greatest impact on the harbor and the environment, the assessment said.
The second-highest score in the evaluation went to a concrete seawall, estimated to cost $2.7 million, but the main difference between the two options was the ease of construction, according to the assessment.
Kahului Railroad Co. built Kahului Harbor in 1900. The original harbor had a berthing area, a dredged channel and a 400-foot-long east breakwater, the assessment says. In 1919, the U.S. Army Corps of Engineers built the west breakwater to a length of 1,950 feet, then extended it in 1931 to its current length of 2,315 feet.
Shoreline erosion has been a longtime problem at the harbor. Since 1899, the shoreline has been receding at an average rate of 2 inches per year.
Public comments on the draft environmental assessment are due Feb. 24. Comments should be sent to the department and the project consultant:
* Department of Transportation, 869 Punchbowl St., Honolulu 96813 (Attention: Eddie Chiu).
* Oceanit, 828 Fort Street Mall, Suite 600, Honolulu 96813 (Attention: Derrick Elfalan).
The assessment can be found at oeqc.doh.hawaii.gov/Shared%20Documents/Environmental_Notice/current_issue.pdf.
* Brian Perry can be reached at email@example.com.