Dam Failure Case Study: Ka Loko Dam (Hawaii, 2006)

On March 14, 2006, Ka Loko Dam experienced an unexpected, catastrophic, and massive breach. Ka Loko Dam was a century-old, 40-foot-high hydraulic fill dam located on the island of Kauai, Hawaii. Owing to a period of heavy but not record-setting precipitation, Ka Loko Dam was overtopped. However, the rain, substantial inflows, and overtopping ceased days prior to the breach.

Although several experts concluded that the dam failed by overtopping, there is substantial evidence to suggest that overtopping was not likely the primary cause or a contributing factor to the failure. Substantial evidence does exist to demonstrate that the likely primary mode of failure was base sliding in a grey saprolite layer beneath the downstream slope of the dam that formed (weathered in place) from concentrated seepage in late-stage volcanic deposits since the construction of the dam in the 1890s. Based on geologic and geochemical analysis, there is evidence of the rapid formation of halloysite clay at key locations in the embankment and foundation. From a stability perspective, the rapid formation of halloysite clay in the form of small, spherical particles created a fragile, sensitive material that became increasingly more susceptible to a progressive sliding failure. The in-place weathering of volcanic deposits into halloysite (clay) has been documented as the cause of landslides in semi-tropical places like Hong Kong, but the Ka Loko Dam failure may be the first known case where in-place weathering caused the catastrophic failure of a major dam. The combination of the presence of late-stage volcanic deposits in the foundation and the substantial duration of dam operation created this dangerous condition. There is a much lower likelihood of in-place weathering for more competent volcanic deposits because of the difference in chemical composition.