Cracks discovered in Green River levee
Published 9:00 pm Wednesday, March 8, 2006
KENT – New and widening cracks across a Green River levee worry engineers that if the support fails, it could flood some of King County’s most valuable real estate.
Damage to the Briscoe Meander Levee occurred after 27 consecutive days of rain in December and January. The stress fractures were visible during a recent visit by Andy Levesque, a county flood control engineer who said the cracks probably run through the levee to the bed of the river.
“It hasn’t cut loose, but you can see that it’s cracking and moving,” he said.
The Green River’s deteriorating levees have been a concern for the county, which determined the levees needed $10 million in repairs to prevent “a potential regional flooding catastrophe.”
It would take $112 million to rebuild levees across the county, widen river channels and move homeowners to higher ground, according to the draft Flood Hazard Management Plan.
Sites along the Green River are at greatest risk, including Southcenter mall, industrial parts of Kent and low-lying parts of Renton. Billions of dollars in housing developments, warehouses and factories are in areas that could be flooded, the report states.
County officials are taking a closer look at the levees after flood waters from Hurricane Katrina breached New Orleans’ levee system in August.
“If you look at the success rate (of New Orleans’ levees), they were about 99.9 percent successful, but it only takes one break to do damage in the billions and billions of dollars,” said Steve Bleifuhs, King County’s river and flood plain manager.
In the 1870s and 1880s, farmers used whatever was available to build the first levees in the Green River Valley. Construction of the Howard Hanson Dam in the 1960s added to the continuous system of levees.
When water seeped under the Segale Levee in 1990, flood-control officials realized the poorly built and deteriorating levees were a problem. Emergency crews had to dig trenches and bring in truckloads of rock and gravel, and despite spending $2.8 million in repairs, work is still needed.
Consultants have been hired to study the Briscoe Meander Levee. Its inner walls are too steep, allowing river sediment to “slump” and take parts of the levee with it.
At Narita Levee at Riverbend, 1,000 feet of a paved trail at the top of the levee has settled and cracked, and the levee’s steep inner slope is “grossly unstable,” the county found. In 1965, the same levee section failed and flooded much of the valley.
The new plan proposes widening selected levees and reshaping their inner walls. The task is made difficult because some warehouses were built near the edge of the levees.
The plan also lays out options for raising $112 million in new flood protection funds, increasing the River Improvement Fund levy, creating new countywide or basin-level flood-control districts, or raising surface-water management fees.
A countywide property tax levy would cost $14.32 a year on a $400,000 home.
King County Executive Ron Sims is expected to send a levee funding recommendation to the County Council in May.
