Thousands of residents living in South King County take their "floodless" region for granted. Nearly 50 years ago the Green River Valley and Duwamish River systems – including Auburn, Kent, Tukwila, Renton, parts of Seattle and other cities – were flooded annually.
The Howard Hanson Dam was built in 1961. Since the last big flood in 1959, many large corporations, including Starbucks and Boeing, have set-up-shop nearby. Two major railways cross the expanse of the valley daily and State Route 167 stretches from one end to the other.And so, it might be asked what the problem is. Expansion is good, correct?
Well, yes, but no, in the sense that a large portion of the region's economy and resources are at risk if major flooding were to occur.
The dam itself is reported to be in fine condition, but the two depressions surrounding the dam found in January and February are cause for concern to residents and businesses. Due to these depressions, the dam is only allowed to withhold a whopping 1/3 of its full capacity.
"If they fill the dam all the way up there's a danger there," said Sarah Miller, emergency preparedness manager for the City of Auburn, "and they don't know how much danger, so they're not going to do it. Filling it most of the way up is what caused the depressions in the first place."
The foundation of the dam is a 10,000-year-old landslide mass. The depressions were found on the right abutment, and engineers have recently performed excavations on the area to gather information about the developing problem.
The smaller depression is reportedly a product of weathering against an engineered filter blanket used to support the abutment. The larger depression is the result of materials settling into a tunnel roughly 30 feet below the abutment, according to Mark Ohlstrom, chief of engineering and construction for the Seattle District of the U.S. Army Corps of Engineers.
The repairs necessary are still not yet known, however. Nor are they expected to be started – let alone finished – before the next flood season starting in mid-October.
The costs of potential repairs are currently ambiguous as well.
"If they need to build a whole new dam or something, it's going to be really expensive," said Miller. "If they just need to put a wall of concrete in it somewhere, it's going to be a lot less. So they just don't know yet."
Various informational meetings have been held to educate local residents about the issue – including one at our own Green River Community College.
The meeting saw roughly 280 residents from the impacted communities on March 31, and those residents were advised to get flood insurance before the next flood season kicks up.
"We always recommend that people get flood insurance, regardless of whether they live in the flood plane or not," Miller commented.
"It's just really cheap if you don't live in the flood plane," she added. "But there's a 30-day waiting period for it, and it's just a good idea to have when you live in a valley with a river in it, with two rivers in it."
The cost of flood insurance varies depending upon the size of your property, whether you rent or own, the amount of coverage you want and ultimately whether you live in an area prone to flooding. However, it is a low estimated $380 per year for maximum coverage on an owned home located outside of the flood plane.
Flood insurance is advised, even for residents seemingly clear from the at-risk regions, but especially for residents and businesses impacted by the depressions.
"You know, the one thing that is important to note probably is that it's not just the flood we're worried about," Miller continued, "because if the flood happens, we lose transportation routes, north, south. Because it puts Auburn Way, West Valley Highway, and 167 all underwater."
In addition to potential loss of transportation, many critical facilities – including power substations, telephone system switches and sewer systems – would be in danger during a major flood.
Not only this, but any goods which would normally be shipped on any major roadways or railways in the Valley would instead have to be shipped east over the mountains then south and back over the mountains, just to arrive at their destination. An unnecessary and expensive procedure, if major flooding can be avoided.
Of major importance, Miller said, is to get flood insurance and stay tuned for further information.
The flood season doesn't start up until mid-October, but that shouldn't give residents the peace-of-mind that leads to procrastination. Any resident or business owner living in the impacted area should get flood insurance.
Keep an eye out for informational meetings when late summer and early fall roll around.
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