Aug 12, 2021
The county’s Department of Public Works is planning to repair the bank of ‘Iao Stream, also known as Wailuku River, to prevent more erosion of the bank, protect the downstream levee and reduce the risk of flooding in Wailuku. COUNTY OF MAUI photo
Saying that delaying action could lead to potential loss of life and extensive property damage, the county’s Department of Public Works is proposing that $1.8 million in repairs go toward a section of Wailuku River.
The department is aiming to upgrade an approximately 240-foot-long section of stream bank located downstream of the Imi Kala Street Bridge and upstream of the ‘Iao Stream Levee 27 for the river, formerly known as ‘Iao Stream, which is part of the Na Wai ‘Eha watershed.
The ‘Iao Stream Levee 27 Repair Project would prevent additional erosion of the bank, protect the downstream levee and reduce the flood risk in Wailuku. It would also include design that can withstand the stream velocity during a 100-year storm, according to the project’s draft environmental assessment published Sunday in the state Office of Environmental Quality Control’s “The Environmental Notice.”
If the project is delayed, erosion that’s deteriorating the embankment could eventually lead to failure of the stream bank and downstream levee, along with flooding of the Wailuku River drainage basin, which could cause “loss of life and extensive property damage,” the report said.
Estimated construction cost is $1.8 million and work is expected to begin next spring to coincide with the end of the wet season. Construction, which would span a project area of 1.39 acres, may take six to eight months, and dates will be announced once a contractor is selected.
Several residential and commercial structures along the right bank are in danger of being undercut if stream bank erosion continues, the report said. Buildings that surround the project area comprise mostly commercial properties, such as Maui Disposal.
In September 2016, heavy rains caused erosion of the Wailuku River bank downstream of the Imi Kala Street Bridge within the project area causing “significant damage” to the existing bank. The County of Maui performed emergency repairs of the stream bank in 2017, and a 2018 assessment showed that boulders placed at the toe of the stream bank washed away, exposing the underlying stream bank along the bottom portion.
The proposed project includes removal of the existing concrete boulder fill slope and grading the slope; excavation to deepen the protection along the toe of the slope to be below the scour depth; and construction of a new revetment system at the toe of the slope to protect against scour. The size and depth of the boulders will be designed to withstand the stream velocity during the 100-year recurrence interval storm event.
Certification that levees can withstand a 1-percent chance flood is required by the Federal Emergency Management Agency; if not certified, flood protection infrastructure is not deemed viable to protect property or life from the 100-year recurrence interval storm event, the report said.
Wailuku River is about 12,000 feet in length from an upstream sediment basin to its outlet into Kahului Bay.
The findings of the environmental assessment process will allow the county department to make an informed decision on its requirement to either prepare an environmental impact statement or issue a finding of no significant impact. If the process concludes that no significant impact is likely, then the county may issue a finding of no significant impact and proceed with the filing of building and construction permits for the project.
To view the draft report, visit oeqc2.doh.hawaii.gov/Doc_Library/2021-08-08-MA-DEA-Iao-Stream-Levee-27-Repair.pdf.
The county Department of Public Works is the determining agency and the consultant is R. M. Towill Corporation.
Comments are due Sept. 7 and can be sent to the County of Maui, Department of Public Works, 200 South High Street, Room 410, Wailuku, HI 96793, or by contacting Kristi Ono at (808) 270-7745 or kristi.ono@co.maui.hi.us.
Comments should also be copied to the consultant at R. M. Towill Corporation, 2024 North King Street, Suite 200, Honolulu, HI 96819, or by contacting Brian Takeda at (808) 842-1133 or BrianT@rmtowill.com.
* Kehaulani Cerizo can be reached at kcerizo@mauinews.com.
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