Process and discharge estimation in ephemeral channels, Canadian Rocky Mountains

Abstract

Process determinations and discharge estimates are made for 10 steep alpine channels in the Front and Main ranges of the southern Canadian Rocky Mountains. The catchments, which range in size from 0.17 to 1.13 km2, are sufficiently small that their runoff patterns are dominantly ephemeral and are characterized by processes that include water floods, debris flows, and snow avalanches.Longitudinal and cross-sectional channel profiles demonstrate the importance of bedrock control and the influence of one or more dominant processes. Debris flow channels have been partially scoured by water floods, and avalanche and debris flow sediments are noted in modified alluvial channels. The distribution and sorting of sediments support the multiple-process origin of specific channels or channel reaches.The discrimination of channel processes is essential for estimates of channel discharge. Slope/area and competence methods employed in fluvially dominated reaches of the 10 channels yield maximum instantaneous discharge estimates of between 1.1 and 12.2 m3 s−1. These discharges are generally not representative of the potential volumes of water and sediment released from the channels because of augmentation by both debris flow and avalanche processes. The design of roads and railways traversing these channels requires consideration of a range of processes of varying magnitudes.