Flooding simulations obsolete
|||State to release Kaua'i reservoir inspection results|
By Jan TenBruggencate
Advertiser Kaua'i Bureau
By Jan TenBruggencate
Geologists and Civil Defense authorities are scrambling to develop new computer models to predict and prevent the damage from the possible failure of any of the more than 100 reservoirs in the state, officials said.
The problem: Hawai'i's existing flood maps are designed to predict the effects on dams of heavy rain — not the sudden and massive injection of water into a stream by a failed reservoir.
The breach of the Kaloko Reservoir's dam, which killed seven people downstream, revealed a vacuum in state emergency planning when it came to dams, officials said.
Ed Teixeira, state deputy director of Civil Defense, said he has called on the Pacific Disaster Center on Maui, an arm of the East-West Center, to apply a dam breach computer program to Hawai'i dams.
"We first used this when we asked them to prepare a dam-failure model for Lake Wilson" on O'ahu, Teixeira said.
Officials said state Civil Defense flood maps, which are based on FEMA maximum stream flow calculations, were never designed to predict the movement of water in catastrophic dam failures.
When Kaloko's dam breached, sending more than 400 million gallons of water sweeping down the rural Wailapa Stream on Northeast Kaua'i, its floodwaters scoured the adjacent land far higher than the edges of the federal flood maps that planners use. Two homes built outside the flood zone were swept away, killing seven people. Another home's lower floor was flooded and several other buildings were washed away.
The center has been working with the technology for several years, but after the Kaloko breach, "it became very high-profile," said Andrea Chatman, senior geologist with PDC.
The technology allows engineers and geologists to simulate a dam breach with computers, predicting the flow of water based on the mapped contours of the land. That information can then be overlaid on aerial photographs that show inhabited areas.
"It's to get a general feel for who and what needs to be evacuated if a dam were to fail," said Jim Buika, senior manager and geologist with the PDC.
The software is sophisticated, but probably won't result in new flood maps for general use in the near future, he said.
"Eventually, I think it will be an important data point for planners, but I don't think the accuracy is there yet," Buika said.
Teixeira said he understands the organization can produce a dam-breach flood prediction in about two hours, but does not know whether the work will lead to a statewide series of dam-disaster flood maps like the tsunami maps in the phone book.
But that kind of information is critical to effective land-use planning, and to help people living in the shadow of dams be able to protect themselves, said Ladye Martin, Kaua'i County deputy engineer.
"I think it just makes sense. People should be aware of what's above them," she said.
For Teixeira, the more critical issue is to do a better job of monitoring reservoirs and regularly maintaining and inspecting dams.
"These things are not supposed to fail. They're man-made. They've got to be man-maintained," he said.
Meanwhile, state and federal engineers have now inspected every reservoir dam in the state, and are preparing reports. Clifford Inn, Department of Land and Natural Resources information officer, said dam inspection reports for Kaua'i are expected to be released by the end of this week.
While state dam engineers have inspected most facilities, the system was not foolproof — a situation that became brutally clear when state Land Board Chairman Peter Young admitted that since the Department of Land and Natural Resources formed its dam safety unit in the late 1980s, it had never once physically inspected Kaloko.
The Hawai'i Dam Safety Program, even after the disaster, is staffed with just 1.5 engineering positions.
It also has become clear that dam-danger ratings are outdated.
The DLNR danger-rating system assesses not the condition of the dam, but the number of people and structures downstream that could be threatened by its failure. In the Kaloko situation, the dam was declared a low-risk dam at a time when there was little but sugar cane downstream. When luxury homes began popping up along Wailapa Stream, the rating system was never updated.
Reach Jan TenBruggencate at email@example.com.