Environmental Review Toolkit
Water, Wetlands, and Wildlife

Washington State Department of Transportation

Watershed-Based Environmental Improvements

photo of a restored wetland
WATERSHED-based measures like Moses Lake Wetland Banking Site (near I-90 in Grant County) store water, provide habitat, recharge groundwater, and provide cultural and recreational benefits. (Tim Hilliard)
photo of a stormwater detention pond
STANDARD measures like this stormwater detention pond (on I-5 near Lacey, WA) have only one environmental benefit: stormwater detention. (Tim Hilliard)

Where should a State transportation agency mitigate construction impacts to wetlands, streams, and other natural resources? What kind of mitigation is best?

In 1996 the Washington State DOT (WSDOT) shifted from a project-by-project approach to these issues to evaluating how environmental mitigation and enhancements fit within the broader ecosystem. Under this "watershed approach" WSDOT examines the value of off-site wetland replacement. Before 1996 WSDOT typically compensated for transportation impacts to a wetland area within the project site. For example, a wetland area may have been created on the inside of a cloverleaf interchange. These wetland replacements often failed, with wildlife struggling to survive within a highway environment. Now WSDOT looks for opportunities to locate its environmental enhancements off site, where the improvements can add greater benefits to the ecosystem - for instance, to upstream areas outside of the highway right-of-way.

WSDOT's watershed approach enables staff to work toward developing a system of interconnected wetlands within a watershed area. And it saves taxpayer dollars when the improvements are not on property directly adjacent to the highway, which is normally considered prime commercial land.

Upfront community and resource agency involvement and early communication with local governments and local watershed groups is a critical factor in WSDOT's watershed approach, as is support from other Department initiatives targeting investments to sites that protect, preserve, or restore key components of the watershed. A Wetlands Strategic Plan and Fish Passage Barrier Removal Grant Program were two of WSDOT's early initiatives. Recent initiatives include efforts such as developing watershed methodologies for meeting permitting requirements, establishing a watershed committee to implement a new State permit streamlining law, incorporating the watershed approach into Endangered Species Act consultations, and coordinating "off-site" mitigation policies into a single policy.

Recently, WSDOT watershed specialists began using the watershed approach to identify and characterize alternative mitigation sites. When they've completed the characterization process, they'll have lists of mitigation options with the greatest environmental benefit. These options will focus on recovering ecosystem processes while at the same time reducing costs through mitigation that restores natural systems rather than creating expensive right-of-way solutions. For example, a restored wetland upstream from a highway construction site might provide as much stormwater control as a vault or a detention pond but it would also provide such additional environmental benefits as habitat, groundwater recharge, and sediment control (see comparison photos).

The WSDOT's watershed approach to environmental improvements has already been tested on two projects: a widening of State Route 522 near Monroe, Washington, and a much larger project involving widening and mass-transit improvements on Interstate 405 between Renton and Bellevue, Washington. The studies identified 195 potential mitigation sites!

For more information visit www.wsdot.wa.gov/environment/watershed

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