Environmental Review Toolkit
Water, Wetlands, and Wildlife

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Existing Gold Creek crossing on I-90 is narrow and provides inadequate space for large mammals to cross. (WSDOT)
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A conceptual view of a proposed crossing alternative. The crossing is expansive enough for large mammals to utilize. (WSDOT)

Washington State Department of Transportation

Interstate 90 Snoqualmie Pass East Project

Large carnivores need to move a lot in order to survive. Small old-growth forest species need to move only a little, if at all. Thanks to planned improvements on a 15-mile stretch of Interstate 90 in Washington State, both wide-ranging and narrow-ranging species will get a new lease on life. And in the process, linkages within the corridor will be restored.

I-90 is the main east-west route across the Cascades into Seattle and areas beyond. The Snoqualmie Pass section of the highway is infamous for its avalanche hazards, its dangerous curves, its deteriorating pavement, and its increasing traffic volumes (more than 58,000 vehicles a day in peak periods). Located within the Wenatchee National Forest, the project crosses a critical north-south corridor for elk, lynx, gray wolf, grizzly bear, and wolverine. The project also cuts through a 25- to 30-mile area of habitat connecting much larger habitat areas along the mountain range. When the I-90 improvements are completed, wildlife conservation will be integrated with highway safety and improved hydrologic functions, water quality, erosion control. and woody debris redistribution (goals of the Northwest Forest Plan).

U.S. Forest Service researchers used GIS technology, snow-tracking, and other techniques to learn how animals got to the highway and where they crossed it...to determine whether habitats were being used as "homes" or as places to travel through...and to understand wildlife distribution along and near the highway.

The next step: Identifying where and how connectivity structures should be built along I-90. A working group of biologists and hydrologists from the Washington State Department of Transportation and State and Federal resource agencies accomplished this task, with input from the Cascades Conservation Partnership, the Alpine Lakes Protection Society, the Mountains-to-Sound Greenway, and the Kongsberger Ski Club.

The group recommended that structures be built primarily at stream crossings, since they represent locations where multiple project and ecosystem needs converge and therefore offer an opportunity for synergistic solutions. The stream-crossing structures should be designed to accommodate aquatic, riparian, and terrestrial habitat features, and they should be built in these seven key linkages: Gold Creek, Swamp Creek, Bonnie Creek, Price Creek, Noble Creek, Hudson Creek, and the Easton Hill wetland area.

The I-90 working group has also recommended ecosystem-conservation strategies such as identifying "hydrologic connectivity zones"—areas where groundwater flow is impeded or can be improved.

What's in the future for the I-90 Snoqualmie Pass East Project? Continued broad public support, for one thing. This month, Washingtonians voted overwhelmingly not to repeal the State gas-tax increase—the funding source for the I-90 project. WSDOT will use some of these public funds to build at least 25 wildlife underpasses and overpasses, some as wide as 30 feet.

For more information contact Larry Mattson at MattsoL@wsdot.wa.gov.

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