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Thursday, June 14, 2012
Oahu's Untapped Hydroelectric Resources
By Henry Curtis @ 2:21 PM :: 11078 Views :: Maui County, Education K-12, Energy, Environment

by Henry Curtis, Life of the Land, Excerpt From Navigating Hawaii's Energy Future, page 100


O`ahu has several large, dammed reservoirs,(262) all of which could provide continuous power to offset intermittent (variable) wind and solar resources. Currently there are no hydroelectric facilities on O`ahu.

Wahiawa Dam, which created Wahiawa Reservoir or Lake Wilson, is located in Wahiawa. It is the second largest reservoir in Hawaii (302 acres) and is owned by Dole Foods. The concrete dam was first built in 1906 on the Kaukonahua Stream, the state’s longest stream (thirty-three miles). The entire Kaukonahua Stream flow is 39 MGD gathered from a drainage basin of ten square miles. The height of the dam is eighty-eight feet and the lake can store 9,200 acre-feet.

Nuuanu Dam, an engineered earthen dam, was first built in 1910 on Nuuanu Stream and reconstructed in the 1930s. Nuuanu Reservoir was originally used for drinking water, but it is now used for recreational fishing and flood control. It is owned and operated by the Honolulu Board of Water Supply. It has a maximum storage of 3,600 acre-feet. The height of the dam is sixty-six feet. The normal water height is thirty feet. Nuuanu Reservoir could store as much as 1.1 billion gallons of water.

Hoomaluhia Dam in Luluku was built for flood control in 1980 and is owned by the City and County of Honolulu. The dam has a height of seventy-six feet. Hoomaluhia Reservoir can hold 4,500 acre-feet.

Kaneohe Dam, on Kamooalii Stream at the base of the Koolau Mountains, has a 4,500 acre-feet capacity. It is an engineered earthen dam, built for flood control, in response to devastating floods in Kaneohe in the late 1960s. Its height is 82 feet.

Dam Acre-Feet / Height (feet) / Stored Energy (kWh)

  • Wahiawa       9,200   88   800,000
  • Nuuanu         3,600   66   230,000
  • Hoomaluhia  4,500   76   340,000
  • Kaneohe       4,500   82   360,000
  • Total   1,730,000 kWh

The Waiahole Ditch (263) is a twenty-two-mile water diversion system that historically took about 28 MGD of windward water to plantation sugar fields on the central O‘ahu plain.264

Lake Wilson Hydroelectric

A hydroelectric facility can be built at Lake Wilson. A large-diameter water pipe can be built adjacent to Kaukonahua Stream along most or all of the stream’s length between Lake Wilson and Otake Camp in Waialua. The pipe could be used to generate in-flow hydroelectric power during periods of peak energy demand.

Some of the water can be returned to the Kaukonahua Stream, which empties into Ki`iki`i Stream about a mile mauka of Kaiaka Bay.

The diverted water could also flow into new non-potable water reservoirs. The advantage of this is two-fold:

First, during the night (10 p.m. to 6 a.m.) wind facilities can produce power but instead sit idle, since they are curtailed by the utility due to low demand. The two North Shore Wind Plants (Kahuku, Kawailoa) could send night-time wind energy to HECO’s Haleiwa (Weed Circle) Sub-transmission Station and then to the lower end of Kaukonahua Stream, just a mile away. The wind energy could then be used to pump water back up to Lake Wilson (pumped storage hydro).

Second, Kaukonahua Stream has periodically overrun its banks, flooding and displacing communities, especially Otake Camp. In addition, major siltation occurs throughout Kaiaka Bay every time there is a heavy rain. The huge watershed gets its water from four Ko`olau streams and two Mount Kaala (Waianae) streams. By siphoning off the stream water into lower reservoirs, electricity would be created, and the flooding and siltation can be avoided.

In all probability hydroelectric could play a large role in firming wind energy.

Honolulu Board of Water Supply (BWS) Power Plants

The Honolulu Board of Water Supply (BWS) system delivers 150 million gallons of potable water and 7.5 million gallons per day of recycled water. Numerous water tanks exist throughout the island. Water can be pumped uphill when there is excess renewable energy on the grid, and dropped during periods of peak demand….

read … Navigating Hawaii's Energy Future


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