CHANNEL-REACH MORPHOLOGY IN MOUNTAIN DRAINAGE BASINS

A classification of channel-reach morphology in mountain drainage basi ns synthesizes stream morphologies into seven distinct reach types: co lluvial, bedrock, and five alluvial channel types (cascade, step pool, plane bed, pool riffle, and dune ripple), Coupling reach-level channe l processes with the spatial arrangement of reach morphologies, their links to hillslope processes, and external forcing by confinement, rip arian vegetation, and woody debris defines a process-based framework w ithin which to assess channel condition and response potential in moun tain drainage basins, Field investigations demonstrate characteristic slope, grain size, shear stress, and roughness ranges for different re ach types, observations consistent with our hypothesis that alluvial c hannel morphologies reflect specific roughness configurations adjusted to the relative magnitudes of sediment supply and transport capacity, Steep alluvial channels (cascade and step pool) have high ratios of t ransport capacity to sediment supply and are resilient to changes in d ischarge and sediment supply, whereas low-gradient alluvial channels ( pool riffle and dune ripple) have lower transport capacity to supply r atios and thus exhibit significant and prolonged response to changes i n sediment supply and discharge, General differences in the ratio of t ransport capacity to supply between channel types allow aggregation of reaches into source, transport, and response segments, the spatial di stribution of which provides a watershed-level conceptual model linkin g reach morphology and channel processes, These two scales of channel network classification define a framework within which to investigate spatial and temporal patterns of channel response in mountain drainage basins.