Changes in Instream Habitat, Large Woody Debris, and Salmon Habitat after the Restructuring of a Coastal Oregon Stream

Elk Creek, a drainage of 26.6 km2 that historically has been severely degraded by logging, floods, and stream cleaning, was restructured in 1986, 1987, and 1989. In all, 106 full-spanning and 94 partial-spanning structures were installed along 4.2 km of stream. An upstream reach of 0.5 km was left untreated. Inventories of stream habitat conditions and large woody debris conducted in 1985 and 1990 (i.e., before and after restructuring), showed that restructuring caused substantial changes favoring suitable habitat for coho salmon Oncorhynchus kisutch; meanwhile, the untreated reach became less favorable for rearing coho salmon. Stream surface area and water volume, respectively, increased 74 and 168% in the treated reach, and 8 and 37% in the untreated reach. Surface area of pool and suitable of channel habitat, the most important summer and winter rearing components for coho salmon juveniles, increased nearly fivefold in the treated reach at summer low flow. In the treated reach, which had a mature riparian area, newly recruited large woody debris was 52% greater in mean length and 60% greater in mean diameter than in the untreated reach, which had a previously logged riparian area. Whereas in the treated reach suitable summer habitat for coho salmon increased fivefold and suitable winter habitat increased sixfold, in the untreated reach suitable summer habitat decreased by half and no winter habitat was available.