The U.S. Army Corps of Engineers’ Mark Ohlstrom tried to explain in the cool, rationale terms of an engineer why Auburn residents needn’t panic about Howard Hanson Dam.
Despite record rainfall in January that stressed the pool behind the dam with the highest water levels it has ever known, the dam itself is sound and poses no risk, emphasized Ohlstrom, the chief of engineering and construction for the Corps’ Seattle District.
Heavy rainfall — 14 inches in 24 hours – also opened two troublesome depressions in the dam’s right abutment.
“We do have an issue of concern, but we don’t know what the significance is,” Ohlstrom told the crowd at the first of two public meetings at Cascade Middle School on Saturday.
Concerns about that abutment lead the Corps to restrict the pool elevation to a third of its normal flood season capacity through mid-March. Now with the dam unable to hold back all the water it was designed to contain, engineers plan to keep watching downstream communities and restricting inflows to cut the risk of flooding, Ohlstrom said.
But Ohlstrom conceded that in the event of an extreme flood like the one in mid-January — unlikely to non existent this flood season he said — the reservoir would probably release inflows with the attendant risk of flooding. Just how extensive or deep is unknown, but North Auburn, much of it below the critical 65 feet sea level, is likely to feel it.
All of which makes Lynda Heinreich, who lives less than a mile from the Green River on I Street in North Auburn, very angry.
“With all the technology available, why has it taken the Corps so long to figure out the problem and do something about it?” Heinreich demanded of Ohlstrom. “How is it we can put a man on the moon, but we can’t fix a dam here on Earth?”
Ohlstrom said that the dam was never designed to eliminate all potential of flooding downstream under any scenarios. Instead, he said, it was designed to reduce the risk of flooding and downstream impacts. Since the dam began operation in 1961 until now, Ohlstrom said, it has done “a tremendous job” at reducing the effects of flooding, making the industrialization and development of the valley all the way up to Southcenter possible.
“Remember that the dam is just one component in a system of trying to do flood damage reduction,” Ohlstrom said. “You also have to look at the levy systems as a key component.”
Among the other components are a series of monitoring wells and a gauge near the bridge over the Green on Eighth Street Northeast.
But it’s the levees that weigh heavily on the mind of Auburn Mayor Pete Lewis.
It is not the single, high-water event that worries Lewis, it is the cumulative “sandpaper” effect of repeated high flows on 100-year-old levees over the course of the estimated two to four years it will take to fix the abutment.
At the moment, Lewis said, the Corps does not know the extent of the needed repairs. Moreover, it doesn’t have the estimated $100 million plus it will need from the federal government to make things right.
The City of Auburn last week released a map showing areas in the city at risk, mostly North Auburn north of 22nd Street Northeast. But engineers said other areas could experience flooding from backed-up storm drains. If the Green River tops its banks, Mill Creek would also flood.
Lewis said that state Department of Ecology policy forbids the city from doing anything in the river to improve the situation, including tree removal or dredging.
“Our hands are tied,” Lewis said.
Carolyn Fitzgerald, chief of water management for the Corps’ Seattle District, told the Tuesday audience that if higher-than-standard flows become necessary, the Corps and local communities have a levee monitoring plan in place. Such a procedure provides experts to walk the levees and provide immediate information to local and federal officials about any impacts or potential impacts to levee protection.
But she said the risk is real.
“All of this translates to high flood risk for all downstream communities,” Fitzgerald said.
The January rainfall resulted in the highest pool of record by about six feet at 1,189. The previous high pool was 1,183 in February of 1996. The maximum flow Auburn can handle is about 12,000 cubic feet of water per second.
“We had inflows at the peak of 30,500 cubic feet per second,” Ohlstrom said. “So if that dam had not been there, we would have had an additional 30,000 cubic feet second of water going downstream.”
Sarah Miller, emergency preparedness manager for the City of Auburn, said the maximum flood damage the Federal Emergency Management Agency (FEMA) will cover is $30,000. Everything else will take the form of low-interest loans. She advised homeowners to consider flood insurance. Everyone who lives within the Auburn city limits is eligible.
