Pacific Salmon (Onchorhyncus spp.) are an iconic species in the northwest coast of the United States. They are an important symbol of regional identity, a commercial and sport fishery and their populations are a critical indicator of ecosystem health. In recent decades, salmon populations have been in decline and many are now listed under the Federal Endangered Species Act (ESA). There are many stressors on these anadromous fish, and access to freshwater habitats is among them. Culverts at road crossings can block fish movement by creating excessive vertical drops, high flow velocities or inadequate water depth and are recognized as a significant conservation issue for salmon and other aquatic species.
Washington State Department of Transportation (WSDOT) is implementing an extensive program to replace hundreds of culverts under State-owned Highways that impede fish passage with fish passable structures. Culverts that restrict stream flows are being replaced with larger stream crossings that mimic natural stream flows. Since 1991, the Fish Passage Retrofit Program has been managed cooperatively between WSDOT and Washington State Department of fish & Wildlife (WDFW). Over 5,000 stream crossings have been inspected on the state highway system. As a result over 1000 culverts have been identified that block significant habitat upstream. Accelerated by the legal requirements of federal treaties with Native American tribes, hundreds of millions of dollars are being invested in inventory, design and construction for stand-alone retrofit projects that restore fish passage at high priority sites. As a result access to hundreds of linear miles of salmonid habitat, once blocked, has been improved at over 300 stream crossings.
The main components for operating this program include: 1) Coordination and partnerships, 2) Field Inventory and survey, 3) Prioritization of projects emphasizing ecological gain 4) Scoping of project corrections, 5) Combining aquatic restoration with terrestrial connectivity improvements 6) Design development, 7) Permitting, 8) Construction, 9) Monitoring, 10) Research
As a result of this work, we have learned that fully replacing barrier culverts with larger structures is a more durable correction with broader benefits for resiliency and maintenance efficiently when compared to retrofits of existing culverts. Successful work also involves developing some specialized knowledge about stream construction which is not commonly held in transportation agencies. Partnerships are critical for addressing watershed restoration needs. To fully realize the ecological benefits of this work, partnerships are often essential to address the conservation needs within watersheds.