Mountain stream adjustments to changes in flow and sediment supply regimes

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Mass movements in mountainous regions often deliver sediment directly to the stream network, resulting in coupled conditions that can trigger immediate channel responses during relatively large delivery events. Notably, delivery events can reset the local channel profile and govern construction and maintenance of channel-bed architecture downstream of delivery points. The local response rate and trajectory following a sediment delivery event is a function of the prevailing watershed flow regime, the event magnitude, gradients in channel width, and in some instances the activity concentration of aquatic species such as salmon. Whereas lowland river systems have been the focus of a substantial body of research, much less work has been carried out within mountain streams and little concerning mountain channel responses to changes in flow or sediment supply regimes.****The objective of my research program is to help build a more complete knowledge base of mountain stream systems, and my principle interest is to examine how these systems respond to changes in streamflow and sediment supply. Changes in either or both streamflow and sediment supply physically manifests itself as a response in local rates and magnitudes of bedload sediment transport. As a result, the central emphasis of my work is sediment transport and, ultimately, I would like to develop predictive capabilities of channel response trajectories under a broad range of conditions, incorporating adequate physical descriptions of sediment transport and channel properties (morphology, texture, structure). Predictive capabilities can serve as a basic tool for natural resource managers and are urgently needed as stream ecosystems face increasingly frequent and/or extreme landscape disturbances due to climate and land use changes.****Looking forward to the next five years of my research program, and within the context described above, I propose to conduct flume experiments and numerical simulations to: (1) describe particle entrainment, travel distance and rest period of individual grains, (2) analyze the development and maintenance of pool-riffle morphologies in response to changes in flow regime and sediment supply (texture and amount), and (3) to study the impact of hydrograph shape and sediment feed regime on sediment transport and bed surface evolution. Experiments conducted in the CFI-funded Mountain Channel Hydraulic Experimental Laboratory provide detailed descriptions of physical processes that are difficult to obtain in a field setting, and numerical simulations are used to further explore responses of the fluvial system across plausible control regimes. The proposed project will substantially develop our understanding of channel stability in mountain streams, which is a critical issue on many fronts - theoretical, management, restoration, conservation - and an emerging frontier topic in fluvial geomorphology.***