By Graham Perednia

The Chronicle

Floods in the Chehalis River Basin are predicted to become more severe over the next half century due to climate change, according to data from a University of Washington climate research group.

That prediction was the focus of a presentation to the Washington State Transportation Commission in Centralia on Wednesday. It was just one topic discussed as local leaders met with the commission for a day-long session at Centralia City Hall.

Along with talk of flooding and its impacts on infrastructure, there were also sessions focused on local city and county transportation, public transit, tourism, economic development and tribal government.

Each year, the Washington State Transportation Commission meets four times in cities across the state to provide a forum for discussion on transportation issues, and this year Centralia was among the stops.

Chehalis River Basin Flood Authority facilitator Jim Kramer told the commission and attendees the predicted level of the 100-year flood will rise to more than 70,000 cubic feet of water per second instead of 50,000 cubic feet of water per second as previously thought. Over the next 50 years, the rate will increase by 60 percent, he said.

The levels are not expected annually, but are the worst case scenario flood that, in theory, would only occur once every 100 years. The predictions are based on the highest flood level recorded in the Grand Mound area, Kramer said.

“The problem is significant and is predicted to get much worse,” he said.

Storms will become worse and generate more precipitation, which will lead to greater volumes of water flowing through the basin, said Bart Gernhart, Washington Department of Transportation southwest region assistant administrator.

The five worst floods in history have occurred in the past 30 years, Kramer said. The worst was in 2007 with a peak flow rate of 80,000 cubic feet of water per second. During the 2007 flood, Interstate 5 was closed for a number of days.

After the 2007 flood, then-Gov. Christine Gregoire created the Governor’s Work Group after the launch of the Chehalis River Basin Flood Authority to create a long-term strategy for reducing flood damage. Gov. Jay Inslee continued the group, which is set to disband this summer when the Office of the Chehalis Basin is permanently established in the Department of Ecology.

The work group has been studying numerous projects throughout the basin, with four alternatives presented by the Department of Ecology last year after intensive environmental studies. The options include a dam near Pe Ell, an improved system of levies and even the relocation of many residents of the floodplain to nearby hillsides, among other options. Upper basin governments largely favored the dam while tribes and some lower basin residents supported the relocation option, which calls for returning the floodplain to its natural state.

Other options include restoration of portions of the Chehalis River and a series of walls and levees along Interstate 5 to prevent the roadway from flooding. Other community projects include raising structures to protect them from floods and building farm pads, which are elevated structures for livestock and heavy equipment to be stored out of the water.

The state Legislature has yet to pass a final capital budget that would provide funding for projects in the basin and allow for the start of the permitting process on a project.

The work group suggested $50 million be allocated to the basin, and the House of Representatives’ version of the budget includes that amount. The Senate version of the budget has $42 million allocated toward basin projects. Regardless of the amount of funding from the state, the region will receive $10 million in federal funds to restore salmon and aquatic habitat. Both chambers of the Legislature must approve the same budget before it can be signed by Inslee.