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Fish Passage Facts

WSDOT’s Fish Passage Barrier Removal Program

 Photo used as an example of freshwater habitat needed by Salmon and other fish for feeding and spawning.
Salmon and other fish need access to freshwater habitat for feeding and spawning.

Salmon and other fish need access to freshwater habitat for spawning and juvenile rearing. Washington State Department of Transportation (WSDOT) recognizes that removing fish barriers is important to the restoration of fish habitats and salmon recovery efforts.

WSDOT’s Fish Passage Barrier Removal Program began in 1991 to identify and remove barriers to fish passage caused by culverts under state highways. This is a cooperative effort with the Washington Department of Fish and Wildlife (WDFW).

How do we determine the number of blocking culverts?

WSDOT works with the Dept. of Fish and Wildlife to identify and prioritize fish-bearing streams and fish passage problems.

WSDOT works with WDFW to evaluate culverts for fish passibility in all fish bearing stream crossings. Physical habitat surveys are conducted upstream from fish barriers to help us prioritize corrections that have the most benefit to fish.

The state wide inventory of WSDOT’s highway system (7,043 miles) was completed in October 2007.

Data from our June 2011 Fish Passage Inventory (pdf 2.6 mb) reported:

  • 6,514 crossings have been inventoried statewide
  • 3,200 culverts in the state system are in fish-bearing streams
  • 1,960 of the culverts in fish-bearing streams were identified as barriers
  • 1,521 WSDOT–owned fish passage barriers that are in need of modification or replacement were identified as having significant habitat gain.*

*Significant habitat gain can be described as adding more than 200 meters (or 218 yards – approximately two football fields) of upstream habitat by removing a barrier from a fish bearing stream.

How culverts can be a barrier:

 example of fishpassage barrier
This culvert on SR 109 is an example of a fish passage barrier because the opening of the culvert is too high for fish to jump into and prevents fish from reaching upstream habitat.
  • Culvert outlet is too high – exceeds the jumping capabilities of the fish
  • Water velocity through the culvert is too fast – exceeds the swimming capabilities of the fish
  • Water depth inside the culvert is too shallow – not enough water for fish to swim through
  • Debris blocks access or creates turbulence that exceeds the swimming capabilities of fish

How we address the problem – our three-pronged approach:

  • Fish barriers are corrected through highway projects, whenever a hydraulic permit is required
  • Stand-alone projects fix high priority barriers on highways that will not be addressed by a highway construction project anytime soon
  • Some barriers are corrected through our Maintenance program, which replaces a failing culvert with a fish passable structure

How are culvert projects prioritized?

Stand-alone fish barrier corrections are prioritized to provide the largest habitat gains for the greatest number of “at risk” fish species, for the best value. 

Prioritizing factors include:

  • Amount of habitat gained for spawning and rearing
  • Quality of the habitat gained
  • The number of species that benefit from the habitat
  • Cost of the project – Costs for barrier corrections cover a wide range – from solutions that modify existing culverts in place to those that entirely replace a culvert with a bridge. 

How are culverts designed to provide fish passage?

When a fish passage barrier is identified and scheduled for correction, WSDOT works with WDFW to pick the best alternative for correcting the fish passage problems. Culvert designs are based on the latest edition of WDFW’s Design of Road Culverts for Fish Passage Manual. This design manual provides a variety of culvert correction options. WSDOT's and WDFW's goal is to select a design that maximizes fish passage for the species found in a particular stream, and can be successfully constructed at that location.

Where feasible, WSDOT and WDFW prefer to use a type of design called “stream simulation” to correct culvert barriers because it best mimics the conditions found in the natural streambed at the culvert site. Culverts designed to simulate natural streambeds are constructed wider than the existing stream channel width, and sloped at a similar gradient as the existing natural stream. Our approach to a stream simulation culvert is a bottomless culvert placed over a natural streambed. Use of stream simulation culverts is based on the principle that, if fish can migrate through the natural channel, they can also migrate through a man-made culvert that simulates the stream channel.

What’s been done so far?

round corrugated steelpipe 
Above: An undersized 11 foot culvert at Mill Creek on US 2 near Stevens Pass was a total fish barrier because the outfall drop was too high.

Below: In 2006 the culvert was replaced with a 38 foot bottomless arch culvert. The new structure restores access to over seven miles of upstream habitat for chinook salmon, steelhead, resident cutthroat trout and bull trout.

 38 foot bottomless arch
  • WSDOT has completed 245 fish barrier removal projects, improving access to 822 miles of potential habitat (as of June 2011)
  • In 2010, 7 fish passage projects were completed opening up approximately 67 miles of potential habitat. 

Where are we heading?

WSDOT is committed to doing its part for the environment by removing barriers to fish habitats.  Our strategy is to continue correcting barriers as part of highway construction projects where we have in-stream work; and to spend money provided by the legislature for stand-alone projects on the highest priority corrections. 

Need more information?

For more information on WSDOT’s Fish Passage Program, call Jon Peterson, WSDOT Fish Passage Coordinator, at 360-705-7499.