Study to predict what will happen if dams fail
How Hawaii dam failures would affect 11 populated areas downstream is the subject of a new U.S. Army Corps of Engineers study on dam safety, the agency announced yesterday.
The $2 million study kicks off this week as engineers attend training classes about computer modeling of floodwater flows, said Derek Chow, the Corps of Engineers project manager. The work is expected to be complete by the end of the year, he said.
IN CASE OF DELUGE
The U.S. Army Corps of Engineers will study the path of flooding downstream if the following 11 dams were to fail. The dams were chosen because of the amount of development downstream, not because of the structural soundness of the dams themselves. To be studied, by island, dam, owner and location, are:
» Nuuanu; Honolulu Board of Water Supply; Nuuanu Valley.
» Wahiawa; Dole Foods; Waialua and Haleiwa.
» Twin; East Kauai Irrigation; Kapaa.
» Waita; Grove Farm; Koloa.
» Elua, Kauai Coffee Co., Kalaheo.
» Aepo; Alexander & Baldwin, Kalaheo.
» Puu Lua; Kekaha Sugar Co., Polihale State Park.
» Hanamaulu, state Department of Land and Natural Resources, Hanamaulu.
» Upper Kapahi, state DLNR, Kapaa.
» Kualapuu; state Department of Agriculture; Hoolehua, Palaau homestead.
» Reservoir 24, Alexander & Baldwin/HC&S Sugar; Paia.
"This is major training," Chow said. "What is going to result from these dam break analyses is going to become standard."
Current estimates of where water would go if a Hawaii dam breaks are what are known as "sunny day" studies because they assume a normal volume of water in the dam, Chow said.
"We're going to get a lot more sophisticated," Chow said, including variables such as 100-year flood scenarios, soil saturation levels and where the dam is broken.
The study will ask, Chow said, "If a dam was to break, what would be its likely break scenario? In which direction is the rush of water going?"
Once that is known more precisely, the state Department of Land and Natural Resources, which oversees the state's dam inspection program, "then decides, working with dam owners, How do we prepare the community for this? Do we set up warning systems, evacuation plans?"
DLNR also must decide whether the dams need to be repaired to make a break less likely, Chow added.
Chow emphasized that 11 dams were chosen for the study not because their structures are at risk of failing, but because they have significant numbers of people living, working or playing downhill from them.
They are Nuuanu and Wahiawa on Oahu; Twin, Waita, Elua, Aepo, Puu Lua, Hanamaulu and Upper Kapahi on Kauai; Kualapuu on Molokai; and Reservoir 24 above Paia, Maui.
The 11 sites were judged to need this kind of study by professionals who have been looking at the state of Hawaii's aging, mostly earthen dams since the tragic breach of Kauai's Ka Loko Dam on March 14, Chow said.
Funding for the study comes from the current federal budget, as requested by U.S. Sen. Daniel Inouye soon after he visited the Ka Loko Dam site last year, Chow said.
It will focus exclusively on how water would flow from the given dams under a variety of situations, Chow said.
The Army corps study is separate from the $5 million in emergency state funds that paid for emergency dam safety inspections of all Hawaii dams after the Ka Loko incident and again after the Oct. 15 earthquakes on the Big Island, Chow said.
The study will be done by corps staff and by engineers with Oceanit Laboratories, SSFM International, PB Americas Inc. and Tetra Tech Inc. Chow said he told the group that although they are normally competitors, he expects them to work together to provide the public with high-quality information about dam safety.
Hawaii Adjutant General Robert Lee, who is in charge of the state Civil Defense program, said yesterday that he welcomes the updated information.
The emergency inspections by the Corps of Engineers and state DLNR dam program after the Ka Loko Dam break have already paid off, Lee said.
Base-line observations made in April were used to compare inspections after the Oct. 15 earthquakes. That comparison is what alerted officials to the need to drain a reservoir above Waimea on the Big Island to make repairs, he said.