Kent escapes first major rains of the season unscathed

The Green River levees and the Howard Hanson Dam had no trouble this past weekend handling the deluge of the winter’s first major Pineapple Express weather system.

The cities of Kent, Auburn, Tukwila and Renton escaped major Green River flooding despite the more than 2 inches of rain that fell Sunday.

“Everything seemed to perform as well or better than expected,” said Casondra Brewster, public affairs specialist for the U.S. Army Corps of Engineers in Seattle, in a phone interview Tuesday. “This was a smaller storm than some we have experienced, but the dam operated as well or better than expected and the levees had no issues.”

That’s good news for the many Green River Valley residents and businesses who have kept close watch on the river since the January 2009 storm damaged the abutment next to the Hanson Dam.

The corps lowered the threat of Green River flooding this winter to 1 in 60 from 1 in 33 last year because of installation of a grout curtain at the dam abutment last year that stood up to summer tests to allow for more storage capacity in the reservoir behind the dam.

But the corps still needs to complete repairs over the next two years to get the Hanson Dam back to full operating capacity when the odds of flooding are 1 in 140. An additional $44 million in repairs, including more drains and the extension of the existing drainage tunnel to put the dam back at its top level, will not be completed until 2012. The federal government provided the funds for the repairs.

The Green River reached a flow of 9,675 cubic feet per second late Monday morning, Brewster said. A flow of more than 9,000 cubic feet per second triggers a King County flood warning alert of moderate flooding, which means the valley upstream of Auburn and Southeast Green Valley Road and the West Valley Highway could have some water over the roadways.

Crews from the corps, county or local cities also start to monitor the levees at a flow of 9,000 cubic feet per second.

“We did really well considering all of the rain we got in the area,” said Mike Mactutis, a city of Kent environmental engineering manager who helps oversee the levees. “There was still plenty of freeboard (extra capacity) left when the flow was highest in the river.”

Corps engineers let water pass through the dam during most of the rainstorm.

“When the flows downstream went up, we starting holding back water,” Brewster said. “But we were at just 5 percent of capacity.”

It takes a flow of 12,000 cubic feet per second before King County issues an extreme flooding alert where levees may overtop because of the rising water.

Brewster said about 4.5 inches of rain fell Sunday up near the dam, far less than the 2009 storm that damaged the abutment next to the dam.

“We had 15 inches in 12 hours in January 2009, so that gives you an idea for comparison,” she said.

Elsewhere during the rainstorm in Kent, a few streets flooded because of Soos Creek and Mill Creek overflowing. The windstorm Monday brought down a few trees and knocked out power to Kentlake High School, which closed early Tuesday. Puget Sound Energy reported about 850 customers were without power Tuesday morning in Kent.

Street crews closed 79th Avenue South between South 259th Street and South 264th Street Tuesday when a tree fell across the road and knocked down a few power lines. PSE crews responded to fix the downed lines.

Crews closed Southeast 256th Street from 156th Avenue Southeast to 146th Avenue Southeast from Sunday to Tuesday because of water over the roadway from nearby Soos Creek. The overflow from Soos Creek also closed a section of 148th Avenue Southeast for a couple of days.

Drivers should avoid driving through large amounts of standing water that cover roads. City crews reopen the roads once water has receded.

For updated street closure information, go to www.drivekent.com.