Maui County is moving ahead with a $1.65 million project to replace a culvert at Waiakoa Gulch and to repair an undermined section of South Kihei Road.
Drainage pipes that run under the road near the Maalaea Surf and Kihei Beach resorts at Sugar Beach are not big enough to handle the high volume of floodwaters that sometimes rolls through the Waiakoa Gulch when heavy rains strike Haleakala.
"Long-term erosion, flooding and overtopping of the culverts from rain events have undermined the upslope shoulder of Waiakoa Gulch culverts at South Kihei Road," a project description says. "The drainage channel on the downstream side of South Kihei Road is usually blocked at the outlet by accumulated sand, which temporarily prevents discharge of stormwater to the ocean. During heavy storms, these circumstances contribute to the stormwater runoff overtopping South Kihei Road, often closing the roadway until the flooding subsides or the drainage channel is open."
Drainage pipes that run under South Kihei Road near resorts at Sugar Beach, shown last week, are too small to handle the amount of water flowing from upstream culverts in Waiakoa Gulch. A $1.65 million project to expand the culverts to handle more floodwaters is moving ahead.
The Maui News / MATTHEW THAYER photo
Current 4-foot and 2-foot diameter culverts under South Kihei Road near Sugar Beach resorts will be replaced by two 3-foot high, 10-foot-wide culverts with new wing walls. The current culverts can handle only 89 cubic feet of water per second while the upstream Waiakoa Uka Bridge at Piilani Highway can handle 8,209 cubic feet of water per second.
The Maui News / MATTHEW THAYER photo
The project's aim is to "repair the critical condition of the deteriorating culverts and road bed."
The existing culverts have a capacity to handle only about 89 cubic feet of water per second, while upstream at the widened Piilani Highway crossing at Waiakoa Uka Bridge, the capacity for a 100-year storm is approximately 8,209 cubic feet per second, according to a project overview.
Plans call for replacing existing 48- and 24-inch-diameter culverts with two 3-foot-high, 10-foot-wide culverts secured in a concrete slab, with new wing walls to maintain the roadway's shoulder, and resurfacing of South Kihei Road. One or two utility poles will need to be relocated.
Recently, "to err on the side of caution," the county installed steel plates over the undermined section of South Kihei Road, said John Smith, the project engineer with the county Department of Public Works. The plates will remain there until the drainage project is completed. Construction work is expected to take about six months.
Engineering work is 75 percent complete, Smith said recently. Funding from the countywide drainage fund has been set aside for the work.
The county has completed a final environmental assessment for the project and issued a finding of no significant environmental impact. That finding was posted last month in the state Office of Environmental Quality Control's current issue of The Environmental Notice. (To see the project's environmental assessment, go to oeqc.doh.hawaii.gov/Shared%20Documents/Environmental_Notice/current_issue.pdf and click on the Maui County Waiakoa Gulch culvert project.)
Because the project involves the repair and maintenance of an existing drainage channel, its special management area permit can be processed administratively by Department of Planning Director Will Spence, according to the environmental assessment.
Bid invitations are planned to be advertised for prospective contractors in June or July.
The project will require some road closures, but Smith said plans for rerouting motorists were ongoing, and consultations need to be done with businesses and other neighbors.
* Brian Perry can be reached at email@example.com.