Introduction: Shortly after the failure of Ka Loko Reservoir dam on March 14, 2006, the USGS made several hydrologic field surveys in cooperation with the State of Hawaii Department of Land and Natural Resources Engineering Division. Results from these surveys were used to compute peak discharges for inflow from Ka Loko Ditch to Ka Loko Reservoir and for Wailapa Stream at Kuhio Highway located downstream of the Ka Loko Reservoir. In addition, peak flood stage was determined for Ka Loko Reservoir, Wailapa Stream at Kuhio Highway, and Morita Reservoir. Morita Reservoir is located between the Ka Loko Reservoir and Kuhio Highway (see map below).

Nature of Flood: Significant rainfall began in mid February 2006 and affected most of the island of Kauai. During the period March 1-14, 2006, USGS rainfall gages at Mt. Waialeale and Hanalei recorded 66.36 and 22.73 inches of rain, respectively. On March 13 and 14 rainfall totals were 7.24 and 4.05 inches at Mt. Waialeale and 4.27 and 1.27 inches at Hanalei. Early in the morning of March 14, 2006, the earthen embankment at the outlet of the Ka Loko Reservoir, which is located in the headwaters of Wailapa Stream, failed. The dam failure caused an estimated 300 to 400 million gallons of water to flow down Wailapa Stream.

Ka Loko Ditch: The peak rate of inflow from the Ka Loko Ditch to the Ka Loko Reservoir was computed to be 205 cubic feet per second. The date of the peak flow was most likely March 10, 2006, which corresponds with the date of the peak flow recorded at the USGS streamflow gage on Halaulani Stream near Kileaua. Beyond direct rainfall to the reservoir itself, discharge from the Ka Loko Ditch is the primary source of inflow to the Ka Loko Reservoir. The peak inflow rate for the Moloaa Ditch, which also flows into the Ka Loko Reservoir, was not determined.

Ka Loko Reservoir: The peak flood stage in Ka Loko Reservoir was determined to be 750.65 feet above mean sea level. The Ka Loko Reservoir water level gage was installed shortly after the dam failure.

Morita Reservoir: The peak flood stage in Morita Reservoir was determined to be 355.10 feet above mean sea level.

Wailapa Stream at Kuhio Highway: Peak discharge on Wailapa Stream at Kuhio Highway was computed to be 27,200 cubic feet per second. The discharge included 26,200 cubic feet per second over the road embankment and 1,000 cubic feet per second through the culvert. The average peak flood stage on the right and left bank of the approach section to Kuhio Highway was computed to be 299.98 feet above mean sea level.

Contact Rick Fontaine at rfontain@usgs.gov or at 808-587-2412 for additional information.