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Spatial and temporal patterns of sediment mobility and storage in a small mountain stream Klinghoffer, Ilana


The study was conducted in East Creek, a headwater gravel-bed channel in the Fraser Valley foothills of the Coastal Mountains of British Columbia. Sediment transport was measured at three spatial scales using two measurement techniques in a study reach containing three unique morphological reaches: rapids, riffle pool, and step pool. At the largest spatial scale, the channel scale, channel stability was assessed between 2003 and 2009 using longitudinal profiles of channel elevation obtained from digital elevation mapping. The longitudinal profiles suggest that East Creek was in a relatively stable state over the six year analysis period, with the majority of erosion and deposition limited to localized fluctuations that varied in magnitude and direction. At the intermediate spatial scale, the reach scale, sediment transport estimates obtained from pit trap and digital elevation mapping data were used to create a sediment budget for the rapids reach and riffle pool sub-reaches of the channel. Using both measurement techniques, erosion and deposition fluctuated and could not be linked to flow regime or sediment supply alone. It is hypothesized that in-stream sediment supply and bed conditioning are important controls on sediment storage, and were used to explain observed fluctuations in erosion and deposition. The magnitude and direction of reach scale sediment storage fluctuations were not consistent across the two measurement techniques; however, elevation mapping estimates were nearly always higher than pit trap estimates. This is likely a result of overpassing of fine material and pit trap inefficiency. At the smallest spatial scale, the unit scale, spatial patterns of sediment transport were assessed across riffles and pools using digital elevation and morphological mapping data. There was increased sediment mobility in pools compared to riffles, which is likely a result of pools containing finer more loosely interacting particles compared to those in riffles. The high resolution unit scale sediment storage data demonstrated conservation of mass and a tight coupling of erosion and deposition in East Creek.

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