Large woody debris in urban streams of the Pacific Northwest

Large woody debris (LWD) performs key functions in undisturbed streams that drain lowland forested watersheds, including dissipation of flow energy, stabilization of bedforms and channel banks, entrapment of sediment, and formation of pools. These functions vary between individual channels, however, depending on the size and morphology of the stream, which in turn depend on climate, watershed size, valley slope, geologic substrate, and relative inputs of water and sediment. Loss of LWD will alter channel form and processes, yielding greater sediment fluxes, more rapid bank erosion and incision, and loss of heterogeneity in bed morphology. Just as LWD is ubiquitous in undisturbed lowland streams of the Pacific Northwest, it is significantly depleted in urbanized systems where it is lost through washout, downcutting, and direct removal. Given the dramatic changes in runoff processes and sediment delivery that typify urban watersheds, we doubt that simple reintroduction of LWD will fully restore the lost functions of urban streams. Instead, projects that replace LWD may be best suited to recover a more limited se