Ko Road Rockfall Hazard Assessment and Mitigation Design

State of Hawaii Department of Land and Natural Resources (DLNR)

Hanapepe, Kauai, Hawaii

Ko Road

Hart Crowser conducted a rockfall hazard assessment of an approximately half‐mile‐long section of Ko Road adjacent to a cliff. After past rockfall events affected the roadway that traverses Hawai‘i Department of Land and Natural Resources (DLNR) land, DLNR contracted Hart Crowser to conduct an evaluation of rockfall hazard along this road segment. Using state-of-the-art photogrammetric methods, we conducted 3‐dimensional analyses of rockfall risk and designed mitigation measures to address the risk. In addition to our modeling, we completed rappelling traverses down the cliff face to confirm the remote sensing data.

Our analyses found a significant public safety risk and evaluated multiple mitigation measures to reduce the risk. Selected mitigation included drapery and anchored netting for different cliff configurations within the project, as well as localized rock bolting for areas with larger unstable rocks.

Our design included a full set of plans and specifications for construction in three phases. Our work included coordination of several nontechnical critical tasks, including traffic contrul, environmental and natural resources assessments and permitting, coordinating access through private lands to the cliff top, and communicating with local public-school personnel to minimize adverser impacts to operations at the adjacent school. Hart Crowser also provided construction observation support for the project.