Report: Dams on Chehalis River won't prevent floods
By John Henderer, The Chronicle,5/6/98
Building a flood-control dam or two on the upper Chehalis River is not the best way to control flooding in the Twin Cities, according to a new report that reverses a consultant's prior recommendation.
The 113-page report released Tuesday does not abandon dams entirely.
Instead, it switches emphasis from damming the upper Chehalis River to modifying an existing dam on the Skookumchuck River, which flows into the Chehalis at Centralia.
The "Pre-Feasibility Analysis of Alternative" by Edmonds-based Pacific International Engineering, a Lewis County consultant, recommends adding an inflatable rubber wier atop Pacific-Corp's earthen dam on the Skookumchuck River in Thurston County.
A second measure calls for excavating 7.2 million cubic yards of dirt - enough to cover a football field more than four times the height of Seattle's Columbia Seafirst Center, Washington's tallest building. The excavation would follow more than five miles of the Chehalis River downstream from the Chehalis-Centralia Airport.
PIE estimated the projects would cost $93.3 million and bring annual benefits of $9.5 million.
"We feel quite strongly now that you can solve the (Interstate) 5 flooding and community flooding without upstream storage (dams on the Chehalis)," Harry Hosey, Pacific International Engineering president, told a technical advisory group Tuesday. "We don't have to go out and permit and build something new."
That's not what PIE told the Flood Action Council, a group made up of local business volunteers, in a November 1996 report.
PIE stated then, "A new dam project with provision of a substantial flood control storage is the only effective means to solve the majority of the existing flooding problem."
County commissioners last year rejected the Flood Action Councils petition to form a flood control district for the Chehalis River Basin in Lewis County.
Commissioners instead formed a countywide flood control zone district, retaining jurisdiction over flooding problems without creating a new layer of government. Commissioners later hired PIE to continue its work.
PIE released its new report Tuesday to a technical team of county, state and federal officials organized by the Legislature as a condition of granting $600,000 toward the work. Already under contract with the county, the PIE study now has $1.1 million allocated toward local flood control studies.
Lewis County is lobbying state congressional officials for $2.5 million more funding from the Federal Highway Administration, said Bob Berg, county director of the General Administration Department.
Officials hope to divert project money that would have been used to raise Interstate 5 toward flood control measures that benefit the freeway and the local community. Raising the freeway 2 feet above flood stage has been estimated to cost $108 million.
"I just hate to go ahead and raise the grade and say, 'To heck with everything else,' when we could form a partnership with the county," Matt Witecki, state Department of Transportation hydraulics branch supervisor, said Tuesday.
Modifying the Skookumchuck Dam has been studied by the U.S. Army Corps of Engineers before, and has been ruled economically infeasible.
In its new report, PIE says the 15-foot high, inflatable rubber wier itself would still be economically infeasible. But combined with floodway excavation and terracing along the Chehalis River, the dam improvement would "overcome the shortfalls" each project has on its own, the report state.
The wier would provide 24,000 acre-feet of water storage, PIE states. An acre-foot is equal to one acre square, one foot deep.
To prevent Interstate 5 from flooding as it did in 1990 and 1996 PIE must reduce floodwaters by 4 feet at the Chehalis-Centralia Airport.
The dam modification would reduce the 1996 flooding level 11.4 feet at Centralia' Pearl Street bridge, the report state.
Excavation work would trim 7 more feet from the 1996 flooding at the mouth of Salzer Creek.
PIE based its recommendations on a flood model it prepared using data from four floods on the Chehalis River.
PIE reviewed new dam proposals for eight sites on the upper Chehalis River system, including two on the Newaukum River, one on the South Fork of the Chehalis River, four on the main stem of the upper Chehalis and one on Elk Creek.
The new dam sites studied on the Chehalis River were near Ceres Hill, Meskill, Doty Canyon and "Charlies Hump" south of Pe Ell. Estimates for each of the eight dams' construction ranged from $82 million at Elk Creek to $423 million on the Chehalis River at Ceres Hill.
The report acknowledges massive excavation along the Chehalis River could result in "a relatively large area of wetland disturbance," for which required mitigation costs "could be substantial."
Officials from the state Department of Ecology queried Hose Tuesday about when he would begin addressing environmental questions.
Hosey said that would happen during the next stage.
The excavation work "has tremendous potential to provide enhanced fish enhancement," he said. "It's just a huge treasure box that's ready to be opened."
PIE is continuing to study the feasibility of its proposals. The technical group reviewed a second-phase work proposal Tuesday that called for river cross-section surveying, "optimization" of the recommended proposals and an environmental assessment.