Week of Oct. 1, 2007

King County Roads Division opens up new territory for salmon homecoming

Spawning salmon return to Cherry Creek near Duvall via a new King County culvert.

Replace failing and undersized culverts – some have been as old as 100 years– prevents road failures, washouts and other serious storm-related damage. But, it also improves wildlife habitat by opening up streams for fish passage and providing wildlife corridors across busy travel areas.

As we enter October and see the return of salmon to local waterways, the Roads Division is winding up another construction season with an emphasis on culvert replacements. Since spring, 13 culverts have been replaced by maintenance and engineering crews, opening up another five miles of stream habitat.

“It’s challenging work,” said County Road Engineer Paulette Norman. “We only have a three to four month ‘fish window’ when we can work in and around the streams, and we also want to work as quickly as possible to keep the roads open to the public.”

Long-time state law requires that barriers to fish passage in local salmon spawning streams be removed, and small, narrow culverts are frequently one of the biggest barriers in the upstream journey. In many cases, the journey home for fish ends when they reach one of these old and narrow culverts.

Norman said most culvert replacement projects average four weeks from start to finish. And although the crews work as quickly as possible, some projects can take up to 10-12 weeks to complete if the excavation for the new culvert is very deep, the old culvert is difficult to remove, or there are problems with the surrounding ground conditions.

With the 13 replacements completed this year, the Roads Division has opened up 70 miles of upstream habitat for fish since 1999. Norman said next year the division plans to replace another 18 culverts.

In addition to benefiting fish, the size, structure and configuration of the replacement culverts have multiple benefits for the county's road system and the traveling public.

Larger culverts increase the safety and function of roads during periods of heavy rain by allowing increased stream flows to readily pass under the roadways rather than overtopping the roads and potentially causing lengthy detours. They also allow woody debris to pass through and reduce blockages during storms that can cause road washouts and localized flooding.

The new concrete box culverts have a longer life, about 50 years compared to 25, than older metal culverts. They also save the county and taxpayers money by reducing the number of road repairs and travel impacts resulting from high-flow damage and work hours spent clearing plugged culverts.

By creating a bigger passage under the roadway, the water loses some of its velocity which reduces soil erosion and scouring downstream of the culverts. And, it allows small mammals to use the culverts as undercrossings, reducing the potential for critter fatalities on roads in the unincorporated areas.

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