By Sharon Michael, The Chronicle , 1/26/1998
The good news is the Chehalis River Basin virtually can be floodproofed.
The bad news is doing so could cost between $40 million and $80 million.
But engineering consultants who based recommendations on a sophisticated computer model say the cost of making structural changes to protect against flooding is cheap compared to the economic impact of floods.
Harry Hosey, Pacific International Engineering project manager, said the cost of Interstate 5 flooding in February 1996 was $50 million a day.
Lewis County Economic Development Council director Bill Lotto said local losses due to 1996 flooding reached $9 million. "We're already paying," Lotto said.
Flooding has been identified by public officials as one factor inhibiting economic growth in the county. Fear of flood damage is said to hold down property values, make it difficult to attract new industry, and cause people to leave the area.
But local flooding has a wider impact when it cuts traffic flow on I-5, the main ground transportation route from Canada to Mexico. Because of the regional impact, state and federal money could be available to pick up the majority of the floodproofing costs.
The three-part solution recommended by PIE, consulting engineers for the Lewis County Flood Control Zone, includes installation of an inflatable rubber weir on top of the Skookumchuck Dam spillway and adding larger outflow structures. That project alone is estimated to cost about $10 million.
The inflated weir would allow the dam to store more water. Additional outflows would allow for the faster release of stored water.
But dam modifications would be just part of the solution, Hosey said Saturday during a meeting of county and city officials.
Excavating under the Mellen Street Bridge, and overbank excavation at other points along the Chehalis River north and south of the bridge, completed the list of "three doable items" that Hosey said would "virtually eliminate flooding" in the basin.
In combination, these modifications could reduce the flood level at Mellen Street from 1 foot to 7 feet. "At a 4-foot reduction at Mellen, it will no longer flood I-5.
"The benefits to the community are tremendous," Hosey said.
"DOT is planning on raising I-5 8 to 12 feet. This is an alternative to raising the highway," Hosey explained.
Costs to elevate I-5 through the Chehalis River flood zone is expected to cost between $60 million and $80 million. Hosey said that estimate does not include mitigation costs.
Hosey said Sid Morrison, state Department of Transportation director, is receptive to PIE's recommendations and has passed on tips about potential federal funding sources. "The timing is right now," he explained.
If money is secured, Skookumchuck Dam modifications could begin in fall 1999. All three projects could be completed by 2002.