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Effects of tributary junctions on longitudinal patterns of riverine heterogeneity are relevant to both fluvial geomorphology and riverine ecology. We surveyed 10 km of small-to moderate-sized mountain channels in the Olympic Peninsula, Washington, to investigate how low-order confluences prone to debris flow deposition directly and indirectly influenced channel and valley morphology. In the Olympic Mountains, debris flows scour sediment and organic material from steep first-and second-order channels and create deposits (debris fans) at tributary junctions in higher-order streams. In lower-energy depositional environments there were statistically significant relationships among debris fans at low-order confluences and gravel substrate, wide channels, and numbers of logs and large pools. Effects of debris fans on channel morphology extended upstream and downstream of fan perimeters, indicating the importance of indirect (offsite) effects of debris flows. Consequently, certain aspects of channel morphology (e.g., pool density, substrate texture, and channel widths) were nonuniformly distributed, reflecting the role of network topology and disturbance history on the spatial scale of morphological heterogeneity. Moreover, heterogeneity of channel morphology increased in proximity to low-order confluences prone to debris flows. In contrast, confluence effects in higher-energy depositional environments were limited. Our field data and information from seven other studies indicate how variation in debris flow volume and composition, stream energy, and valley width at the point of deposition influence the relationship between low-order confluences and channel morphology. Keywords: slope stability, fluvial geomorphology, debris flows, natural hazards.

Large, infrequent fluxes of sediment to streams by mass wasting are intrinsic to the erosion regime of mountain drainage basins. To elucidate the role of mass wasting in the construction and evolution of steep land channel environments, it is crucial that we identify the processes involved and recognize their legacy on the valley floor. In the winter of 1996, nine storm-triggered debris flows carried ~18 000 [m.sup.3] of coarse debris into the upper reaches of the South Fork of Gate Creek (Oregon Cascade Range) during flood flow. Analysis of resulting channel morphologies and bed textures shows that the sediment moved downstream as a wave-like pulse or pulses, overwhelming the channel and causing it to braid, with flooding and alluvial deposition over the valley floor. Downstream progression of the sediment wave resulted in vertical accretion of the valley floor with sediment carried as bedload, the maximum depth of valley-floor burial being set by the amplitude of the wave. Passage of the wave left a channel incised to bedrock, inset between coarse-grained alluvial terraces. This study examines the genesis of these features at Gate Creek and points to such terraces as field indicators of massive episodic influxes of sediment and the associated formation of fluvially transported sediment waves. Keywords: debris flow, fluvial transport, sediment supply, sediment transport, terraces.

Examines the recruitment of wood to streams on redwood forests in Northern California. Impact of logging-related debris and high forest mortality rates in conifer and deciduous forests on second-growth forests; Role played by wood in the geomorphology and ecology of streams and rivers; Variation in source distance curves across second growth sites.

Makes observations on the effects of punctuated sediment supply on valley-floor landforms and sediment transport at Gate Creek in the Oregon Cascade Range. River channel responses to mass wasting; Variation of downstream terrace height; Particle-size distributions; Mechanisms that maintain a sediment wave; Factors affecting formation and life of a sediment wave.