King County creek being diverted to save a bridge

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by GLENN FARLEY / KING 5 News

Bio | Email | Follow: @GlennFarley

KING5.com

Posted on September 14, 2010 at 5:57 PM

NEAR SNOQUALMIE FALLS -  It's name is Tokul Creek.

They should have called it a river.

That's because this creek turns into a major torrent during big rains like the one in early 2009 that began eating away at the bank. The bridge that links the town of Snoqualmie to Fall City on state Highway 202 isn't at risk of collapse, but engineers feared it could be shut down if more of the bank that holds the bridge up were to be wash away in the next big rain.

"The major concern was as this is eating through the banks," said engineer Amir Ahmadi. "That the bridge that is right now serving the commuters would wash away."

Construction equipment now surrounds the bridge as part of a $1.5 million effort to make sure the earth that holds it up is stabilized. But to get some of that equipment down the steep bank in order to work at the bottom, the creek had to be diverted - a flow rate that state engineers say is about 40 cubic feet per second.

The contractor is blocking water with water, using a series of "aqua dams" -  heavy plastic bags filled with water that feel like gigantic water beds to walk on. The creek bed, which had about two feet of water in it three days ago, is now virtually dry. The water is now flowing through large, plastic pipes through the work site.

Biologists say about 1,500 fish were successfully removed and crews are still finding bottom feeding sculpins and a few other fish alive in pools.  When found, they are rescued and returned to the creek. 

The current bridge was built in 1984. Ahmadi says part of the problem is that two concrete bridge piers were left in the creek bed after the old bridge was torn out back then. Those leftover piers tend to snag downed trees and other floating debris, forming a dam in major flood events like one in 2009.  With nowhere else to go, the force of the water is then is directed toward the bank that supports the new bridge.

The money for the job is coming by way of an emergency federal grant.  But the window is narrow. The contractor has to have the walls of the creek that support the current bridge armored with rock in little over a month, before the rainy seasons starts ramping up in October.

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