Kuhio Highway, Kauai

Hanalei Hills Landslide Mitigation along Kuhio Highway (Route 560) on Kauai secures a critical North Shore route at Mile Marker 1 near Hanalei Bridge, where a massive March 2021 slope failure from heavy rains dumped over 80,000 tons of debris across the road, severing access to Hanalei and beyond. This $24 million project, completed in late September 2025 after four years (with 80% federal funding), restored two-way traffic reliability for locals, tourists, and emergency services on Kauai's only land route to the scenic North Shore, addressing vulnerabilities from flooding, old irrigation tunnels, and steep terrain.​

The effort unfolded in three phases: Phase 1 (2021) built a shotcrete wall and installed 500+ soil nails up to 40 feet deep for emergency hold; Phase 2 (2023-2025) added 800 more nails, anchored wire mesh via helicopter lifts, and minimized daytime disruptions with night work despite single-lane limits; Phase 3 rerouted hillside water through pipes to the Hanalei River, repaved the road, upgraded guardrails, shoulders, and drainage during full nighttime closures from July to September 2025. It boosts resilience for the area's tourism-dependent economy and communities, though adjacent Waikoko slope work wraps up by January 2026.​

From a technical standpoint, the stabilization anchors the slope above and below the highway with over 1,300 soil nails grouted into bedrock, double-layer wire mesh draped and tensioned across sheer faces to catch rockfall, and shotcrete facing for erosion control, all tied to an upgraded drainage network capturing runoff from a discovered irrigation tunnel that triggered the initial slide. Engineering tackled logistics on a narrow, high-traffic switchback with phased construction, helicopter ops for mesh, and BMPs for stormwater to protect the Hanalei River watershed, while pavement overlays and 10-ton weight limits (ongoing above the site) enhance load-bearing for heavier vehicles post-repair.