Aepo and Elua Reservoir Systems Dam Break Analysis (HI)
The heavy rains of February 2006 and the subsequent failure of Kaloko Dam on the Island of Kauai prompted a major disaster declaration and led to the implementation of detailed dam failure inundation studies for critical reservoirs on the major Hawaiian islands. WEST Consultants was contracted to conduct hydrologic and hydraulic analyses to determine the dam breach floodplain below Aepo and Elua Reservoirs on the Island of Kauai. The scope of work included site visits, hydrologic modeling, hydraulic modeling, inundation mapping, technical meetings, and reports.

Aepo Reservoir is located within Aepo Gulch, on the south side of the island of Kauai. Aepo Gulch contains a series of storage and distribution reservoirs including the Aepo, the Aepoalua, the Aepoekolu, and the Aepoeha Reservoirs. The Aepo Gulch reservoirs store irrigation water for distribution to downstream agricultural lands.

Elua Reservoir is also located on the southern slope of the island of Kauai, in the town of Kalaheo, just north of Highway 50. It is roughly 13 acres in area, with an impoundment volume of 135 acre-ft at normal pool elevation. Flow from the reservoir drains to the downstream Ipuolono Reservoir.

Hydrologic Engineering Center Hydrologic Modeling System (HEC-HMS) models of the two watersheds were created based on available geographic and hydrologic data to estimate the 100-year, 24-hour and Probable Maximum Precipitation (PMP) event inflow hydrographs. HEC-RAS hydraulic models were used to route the Probable Maximum Flood (PMF) inflow hydrograph through the reservoirs, simulate dam breach conditions, and route the flood downstream to the Pacific Ocean. Both “sunny day” and PMP-induced dam breach scenarios were considered. Results of the hydraulic analysis were used to define dam breach floodplains and create dam breach inundation mapping. Cost $185,000.