Kaumalapau Harbor, Lanai, Hawaii, Two-Dimensional Breakwater Stability Study

A two-dimensional breakwater study was conducted to examine the effects of design and above wave conditions on the stability of the proposed breakwater rehabilitation at Kaumalapau Harbor, Lanai, HI. Additionally, it was desired to determine what effect, if any, cost reducing construction modifications would have on breakwater stability. The modifications examined were combinations of reducing the crest elevation and raising the armor layer toe elevation. Results of the study were compared to results of a previous three-dimensional study of Kaumalapau Harbor (Smith 1998). Inferences were made to estimate the effects the modified wave and bathymetrical conditions would have on stability of the breakwater head. Five stability plans were studied in a wave tank at a 1:54.3 (model to prototype) scale. The model consisted of a IV: 10H nearshore slope to simulate prototype bathymetry, which was not included in the three-dimensional study of Smith (1998). All plans were constructed using Core-Loc armor units. Plan 1, the recommended plan from the three-dimensional study, was constructed of 17.8-tonne Core-Locs on the sea side and 32.2-tonne on the lee side. Results from Plan 1 experiments indicated that the 17.8-tonne Core-Locs were not stable for 12-sec, 8.5-m waves. Plans 2 through 5 were studied to determine the optimal breakwater design using 32.2-tonne Core-Locs on both the sea side and the lee side.