King County executive: $10M to $35M needed to protect people, facilities in flood-prone Green River valley

King County Executive Kurt Triplett will ask the County Council for $10 million to $35 million to protect and possibly evacuate jail inmates, courts, animal shelter and county offices in the flood-prone Green River valley.

Some offices, including election headquarters on Southwest Grady Way in Renton, may be permanently moved to a new location.

Assistant County Executive Pam Bissonnette told the council's Committee of the Whole this morning Triplett will give the council more detailed information about how county operations can continue — and what that will cost — if parts of Kent, Renton, Auburn and Tukwila are flooded by water released from the damaged Howard Hanson Dam.

Triplett has asked the council for authority to declare an emergency in advance of a flood so the county can prepare quickly without red tape.

The Army Corps of Engineers, which owns and operates the dam, is currently installing an underground "grout curtain" intended to slow the seepage of water through a hillside abutment that has reduced the amount of water the dam can safely hold.

But Bissonnette said the Corps doesn't expect to complete a permanent solution — most likely a concrete cutoff wall — for another three to five years. That option would cost "hundreds of millions of dollars," she said.

In the meantime, the Maleng Regional Justice Center in Kent, King County Elections, Aukeen District Court in Kent, the Kent animal shelter, several public health clinics and the Department of Development and Environmental Services are at risk of flooding.

Under worst-case scenarios, Development and Environmental Services could be flooded with 7 feet of water and Elections with 10 feet. Bissonnette said it might be necessary to relocate Elections before flood season to avoid the possibility the November election will be disrupted.

Bissonnette wasn't able to quantify the likelihood of flooding, but said the levees that hold back the Green River were designed with the assumption that the Howard Hanson Dam would hold back most stormwater from the upper watershed. Now the county is faced with the prospect of "more water more frequently."

Thousands of businesses and residents also are at risk. Since the dam went into operation in 1962, the Green River Valley has become the largest warehousing district in the state. The Federal Emergency Management Agency estimated in a draft report that a flood could cause $2 billion to $3 billion in property damage, Bissonnette told the council.

An earlier report commissioned by the county found that severe flooding would cause $46 million in economic disruption per day.

Keith Ervin: 206-464-2105 or kervin@seattletimes.com