Alexander Dam is a hydraulic fill earth dam and the second-highest embankment dam in Hawaii, having been built in 1929–1932 on the south side of the Hawaiian island of Kauai to provide irrigation for McBryde Sugar Company Ltd. It was constructed across Wahiawa Stream mauka (Hawaiian for “stream that comes from the mountains,” literally “toward the mountains”), upstream of Kalaheo, to store 800 million gallons (5 million m3) of water to irrigate sugarcane fields. The embankment dam was intended to have a maximum height of 125 ft (38 m), a crest length of 620 ft (189 m), and a maximum base thickness of 640 ft (195 m). The total design volume was 580,000 yd3 (443,120 m3) and consisted of hydraulic fill sluiced to the dam site and supporting shell material. On March 23, 1930, a 60-ft- (18.3-m) wide section of the core pool suddenly dropped ∼30 ft (9.1 m) and moved downstream, rapidly draining the core pool and enlarging the mass. The embankment was at a height of 95 ft (29 m) and 78 percent complete when the failure occurred. The failure occurred so quickly that it killed six workers and injured two others on the downstream face. The volume of slide debris was ∼275,000 yd3 (210,100 m3). Thirty feet (9.1 m) of the embankment's core stood near vertical after the failure, leading engineers to believe that the materials making up the downstream shell had consolidated sufficiently to inhibit internal drainage. The embankment was rebuilt by emplacing a 40-ft- (12.2-m) high rock buttress across the downstream toe, widening the downstream shell, and installing tile drains to facilitate internal drainage. The retrofitted structure was completed in December 1932 and remains in service some 85 years later.

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