Rockfall Risk Assessment Burleigh Head National Park

An assessment of rockfall risk and control options for the Burleigh Head National Park, Queensland is presented. The park consists of a headland which rises from a basalt boulder beach to a rain forest covered plateau approximately 70 m above sea level at a slope inclination of 35o to 45o from horizontal. The basalt cap, which forms the plateau, is columnar jointed with the columnar blocks typically 1 m in diameter and 1.5 to 3 m long. Columnar boulders from the plateau occasionally fall, bounce, roll and slide down the lightly vegetated slope towards the beach with some of the boulders landing on or passing the Ocean View Circuit walking track near the base of the slope. Many of the recent rockfalls have occurred during or immediately after an intense rainfall event or period of prolonged rainfall. A quantitative assessment was undertaken to determine the risk to people walking along the Ocean View Circuit being struck by rockfalls and the risk reduction capabilities of various remedial work options. Probabilistic analysis of rockfall trajectories was undertaken using the computer program ROCKFAL3 to produce distributions of boulder kinetic energy, bounce height and stopping distance relative to the walking track. Both total annual risk and individual risk were calculated. Risk levels were compared with various published acceptable risk criteria to determine if remedial action is warranted. The risk reduction capability of scaling operations, rockfall catch fence construction and temporary track closure during high risk periods was assessed. Catch fence design requirements were determined from ROCKFAL3 probability distributions.