A PASSAGE TO HABITAT

The Story of Culvert Prioritization in the Siuslaw Watershed

Culverts, like dams, were not seen as a serious problem for fish when they were initially installed. Road builders were concerned about preventing flooding and road washouts. Also, blocking fish passage to small headwater streams did not seem to warrant the expense of designing and installing a culvert that would reliably pass fish for many years.

However, by the time many watershed councils began forming in the 1990s, fish passage, especially culverts, had become a major issue. The image below shows why.

Culvert Map: Siuslaw Watershed Council

Culvert Map (Siuslaw Watershed Council)

This map shows the location of the culverts in the Siuslaw watershed. Many of these culverts block fish passage for multiple reasons. The jump required might be too high for adult fish. There might not be a good pool beneath the outflow for fish to jump from. The culvert might be too small or the water velocity too high. In addition to blocking passage by adult fish, juvenile fish and smaller aquatic organisms need to be able to move upstream to seek refuge during large storms or simply for better habit. Reopening habitat by replacing culverts is one of the most cost-effective ways to help restore salmon populations.

Watershed Professionals Network, Oregon Watershed Assessment Manual, 1999

Watershed Professionals Network
(Oregon Watershed Assessment Manual, 1999)

But with thousands of culverts in the basin, and the high cost of culvert replacement, which culverts should be replaced first? This is the question Todd Miller, Coordinator of the Siuslaw Watershed Council, has been working on for several years. Todd and members of the Council saw that too often culvert replacement was done only when road maintenance required it. Consequently, they created a strategy for prioritizing culvert restoration. The prioritization list includes:

  1. focus on restoring areas with high ecological value for wild coho
  2. work from downstream to upstream
  3. remove barriers that block all passage before removing partial barriers
  4. replace culverts that block longer reaches of stream
  5. evaluate if the road that the culvert supports is still needed
  6. coordinate culvert replacement with in-stream riparian restoration

However, there is a key factor that has made the Siuslaw Watershed Councils approach highly successful. "We use different assessment techniques to determine where the best ecological potential is for salmon recovery. Then we overlay that information with the social context of willing landowners who want see spawning salmon back in their streams."

Todd Miller, Coordinator of the Siuslaw Watershed Council

Todd Miller, Coordinator of the Siuslaw
Watershed Council (John Ame)

Prioritization also helps landowners and the general public grasp the salmon recovery effort because it breaks down the issue into smaller, more manageable pieces. Todd says, "When we can go to a landowner, like a timber company, and say, Look, we have salmon data on everything in this area except for this little square that you own. Then the landowner is more comfortable working with us because were not asking them to just hand over data for everything they own."

The prioritization work is still just the beginning. A watershed council, like the Siuslaw Watershed Council, then has to select specific culverts to be replaced and apply for grants to help fund the replacement. Money for culvert replacement comes mostly from the Oregon Watershed Enhancement Board, the US Forest Service, and the Bureau of Land Management.

With prioritization more streamlined, money for restoration efforts can be allocated where it is most effective.

To learn more about fish passage restoration in the Siuslaw Watershed, explore the Siuslaw Watershed Council interactive case study.