Wednesday, August 25, 2010

Tryon Creek Restoration Efforts

Yesterday, I went for a walk in the park. That’s right, Tryon Creek State Park. Jen and I were conducting the biweekly spawning ground survey in Tryon Creek. For those of you who are unfamiliar with the creek, it is a relatively undisturbed urban watershed. Most of it lies within the boundaries of the state park in southwest Portland. Historically, the creek probably supported abundant populations of anadromous fish. Now it seems that most of those fish populations may be depressed. One of the reasons for this may be a culvert running under Highway 43 which was constructed in the late 1920s. The design most likely blocked lamprey migration and was not ideal for salmonid passage, either. The baffles within the 400 foot long culvert were not fish friendly and the drop at the outlet of the culvert was too high for fish to negotiate at times.

Back in 2003, the City of Lake Oswego secured a Metro Greenspaces grant to analyze the best alternative for replacement or removal of the culvert under Highway 43. Soon the Oregon Department of Transportation came up with some more money. Lots of other partners became involved as well.

In 2006, our office began a project to monitor the effectiveness of restoration actions. We began by determining the existing habitat conditions and the presence, absence, and distribution of lampreys and salmonids, both above and below the culvert. Larval lamprey of two species were captured below the culvert, but none above. Cutthroat trout, steelhead/rainbow trout, coho, and Chinook salmon were found both above and below the culvert.

Culvert Baffles - Before and After

In 2008, the baffles in the culvert were replaced and the drop at the outlet of the culvert was reduced with a series of natural step pools. Restoration efforts are ongoing in the portion of creek below the culvert to improve fish passage. We continue to monitor the presence of fish in Tryon Creek to determine the success of the restoration effort to improve fish passage through the culvert.

Fish Passage into Culvert - Before and After

In 2009, no lampreys were found in any section of Tryon Creek. The same species of salmonids were found both above and below the culvert. Cutthroat trout spawning activity was observed above the Highway 43 culvert as well. Still, it is too early to determine the effectiveness of the restoration work.

We will continue to sample Tryon Creek to further our understanding of all fish species within the system. Monitoring will provide further evidence for the level of success of the improvements made to the culvert and to the creek below the culvert as well as the efficiency of passage through the culvert by lampreys and salmonid species.

For more information, read the latest report.

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