Ecological - Second Order
Forty-six debris flows in a fifth-order basin in the Oregon Coast Range, U.S.A., were studied to determine the role and significance of debris flows in sediment routing. Dating of charcoal from basal colluvium in three bedrock hollows and in one first-order channel yielded an average landslide recurrence interval of approximately 6000 years. This resulted in recurrence intervals of debris flows in first- and second-order channels of respectively 1500 - and 750 years. These time intervals were used to construct sediment budgets for first- and second-order basins, which, in conjunction with textural analyses of colluvium in hollows and sediments in channels, indicated that first- and secondorder basins store the majority of sediments supplied to them by mass wasting and release it periodically by debris flows. The transport of a majority of sediments to thirdand higher-order channels by debris flows implies a strong stochastic character in the routing of sediments through basins that may include alluvial channels alternating between conditions of aggradation and degradation and armoring over time scales of 10^ to 10-^ years.