Particle kinematics and sediment transport processes in mountain streams: the role of sediment supply and flow regimes

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Despite a large body of research on sediment transport, no agreement has been established on a governing equation appropriate to the estimation of bulk sediment movement in stream channels over time. In part, this is due to the irregularity of the granular beds acted upon by temporally and spatially variable fluid forces, bedsurface structures and armouring, and episodic sediment supply. Indeed, bed surface composition (texture and structure) and the sediment supply/storage regime both play important roles in controlling channel stability and regulating sediment transport in streams. Mountain streams are especially complex; stones form structures that exert significant influences on both the mobility of the bed sediment and the nature of the flow. In addition, these streams episodically receive large inputs of sediment from adjacent hillslopes, potentially dominating channel morphology and system dynamics. Although many studies have investigated the dynamics of lowland rivers with less variable sediment and flow regimes, little research has focused on mountain streams. The proposed research will focus on a set of questions related to the impact of sediment supply and flow regimes on the variability of particle displacement and retention, streambed texture and structure, bed stability and channel morphology. Understanding which portions of the stream bed are mobile, the frequency of sediment movement, and channel response and recovery all constitute important pre-requisites for the accurate prediction of those flow and sediment disturbances that can be attributed to climate and land-use changes on stream ecosystem. This study will focus on small-scale experimental units (laboratory and field), in order to gain in-depth mechanistic understanding of linkages between sediment supply and flow regime with channel stability and morphology. A key objective is to use the experimental and field results to develop and parameterise models so as to enable predictions of channel response/recovery in relation to changes in sediment and flow regimes in mountain streams. Field observations will be complemented by laboratory experimentation, in turn facilitating the development of protocols and methods for future field-based research. Quantification of the relation between channel response/recovery and changes in flow and sediment supply regimes will be based on: (a) description of individual particle displacement and retention, and (b) quantification of sediment supply-transport relations.