Results

The results of the habitat assessments indicate that channel and habitat structure of a number of the segments in most streams are frequently degraded relative to values from published “properly functioning conditions” for the Puget Sound or the Pacific Northwest region. For example, bankfull width to depth ratios are often larger than prescribed properly functioning conditions ratios, suggesting that channel dynamics are unstable. Pool habitat frequencies are lower than standards and of low quality in most segments. This decreased slow water “rearing” habitat may limit juvenile carrying capacity as well as hinder upstream migration by adult salmon. In addition, instream habitat complexity and large woody debris (LWD) abundance and quality are significantly degraded, exacerbating rearing habitat deficiencies and compounding the hydro-geomorphic instability. The low amounts of instream LWD may be partially responsible for the low pool frequency. LWD frequency was closely related to pool frequency in most study streams as it is in undisturbed streams of the Pacific Northwest.

These data suggest that processes creating natural habitat structure may be changed from natural conditions. Analysis of basin land cover reveals less forested and increasingly impervious cover, as well as a significant loss of wetlands, which has been shown to alter the basin hydrologic regime. This change in basin hydrology leads to destabilization of channel morphology. Riparian vegetation also seldom resembled natural conditions and was nearly completely depleted of sources of high quality, coniferous LWD. Dominant riparian vegetation often included landscaping, invasives, and young deciduous forest.