Marwan A. Hassan – University of British Columbia
Nisreen Al-Ghorani – McMaster University
Sol Leader-Cole — University of British Columbia
Conor McDowell — California State University, Sacramento
Anshul Nadav — Indian Institute of Technology Roorkee, Roorkee
Kevin Pierce – University of Oslo
Jiamei Wang – Tsinghua University
Matteo Sellati — Fisheries and Oceans Canada (DFO)
Enrica Viparelli — University of South Carolina, Columbia
Tianqi Xing – University of British Columbia
Mass movements often deliver sediment directly to the mountain stream network, often causing a drastic response after relatively large events. These events can reset the local channel profile, change the streambed texture, and export large sediment volumes, ultimately governing channel stability. The questions of how, when, and why mountain channels become unstable is related to the flow and sediment supply regimes along the channel. The complex morphology of mountain streams consists of grains of different sizes and shapes, which affects hydraulic variables through flow resistance. Consequently, this morphology impacts sediment mobility and transport, driving the adjustment of this same morphology. In this presentation, we explore how mountain rivers adjust until they fall into a “stable” state for a given combination of sediment supply (texture and volume), water flow (magnitude, duration, and history), channel gradient, and bed morphology. In steep mountain streams, these stable channels are attained by the development of bed structures, with the step-pool morphology being the most stable. In lowland streams, the pool-riffle morphology is the common stable state, as it enables the vertical accumulation (and diminution) of stored sediment as the controlling variables change. To explore the processes that control bed stability along the channel network, we report results from field observations of step-pool, plane-bed, and pool-riffle mountain channels along with paired flume experiments.