HDR: Kenai bluff‑stabilization construction complete; monitoring, vegetation expected to show stability in 1–2 years
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Summary
HDR engineering told the Kenai City Council that construction of a roughly 4,700‑foot bluff‑stabilization berm finished in October, placing more than 60,000 cubic yards of rock; engineers said the structure protects the bluff toe from episodic wave/ice events, but long‑term bluff retreat due to chronic processes will require vegetation and monitoring.
Ronnie McPherson of HDR Engineering updated the Kenai City Council Dec. 3 on the bluff‑stabilization project and described construction, performance expectations and monitoring plans.
McPherson said construction—completed Oct. 11—used a barge‑based method to place about 26,500 cubic yards of armor rock and roughly 36,000 cubic yards of core and bedding rock along about 4,700 linear feet of bluff from Cemetery Creek upstream. The armor, bedding and a geotextile composite were installed so the toe of the bluff resists wave action, storm surge, river current and sea/river ice; the downstream portion was sized primarily for ice forces.
He said the structure is intended to stop toe‑undermining and thereby reduce episodic erosion (storm events). Chronic erosion driven by wind, groundwater and stormwater runoff is still expected until vegetation establishes a quasi‑equilibrium slope; McPherson said visible vegetation gains and other stabilizing signs could appear within 1–2 years. HDR will provide an operations‑and‑maintenance manual with monitoring recommendations, and staff discussed creating an inspection path and possible controlled access after vegetation is established.
Council members asked about design life, whether additional fill or heavy vibration treatments would be advisable (engineer cautioned against heavy equipment at the bluff edge), ice plucking considerations (addressed via slope design), and whether utilities in zones of potential retreat might be active; HDR advised vegetation and thoughtful monitoring rather than introducing major fill at select short sections.
McPherson said the project’s water‑based barge construction enabled completion in a single construction season and that the Army Corps of Engineers performed feasibility and geotechnical work and led construction management on the project.
