Annual bed-elevation regime in the alluvial channel of Squamish River, Southwestern British Columbia, Canada
✍ Scribed by Alan D. Paige; Edward J. Hickin
- Publisher
- John Wiley and Sons
- Year
- 2000
- Tongue
- English
- Weight
- 684 KB
- Volume
- 25
- Category
- Article
- ISSN
- 0360-1269
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✦ Synopsis
The aim of this study is to examine the annual regime of channel scour and fill by monitoring bed-elevation changes in a reach of Squamish River in southwestern British Columbia, Canada. Sonar surveys of 13 river cross-sections in a sandy gravel-bed single-channel study reach were repeated biweekly over a full hydrologic year (1995/6).
The survey results show that bedload movement occurs as waves or pulses forming bedwaves that appear to maintain an overall coherence with movement downstream. These bedwaves propagate downstream by a mode here termed pulse scour and pulse fill, a process distinguished from the conventional mode of scour and fill commonly associated with flood events (here termed local scour and local fill). Bedwave celerity was estimated to be about 15Á5 m d À1 corresponding to a bedwave residence time in the study reach of almost one hydrologic year.
The total amount of local bed-elevation change ranged between 0Á22 m and 2Á41 m during the period of study. Analysis of the bed-elevation and flow data reveals that, because of the bedwave phenomenon, there is no simple relation between the mean bed-elevation and discharge nor any strong linear correlation among cross-sectional behaviour. The bed-elevation data also suggest that complex changes to the bed within a cross-section are masked when the bed is viewed in one dimension, although no definitive trends in bed behaviour were found in the two-dimensional analysis.
Although a weak seasonal effect is evident in this study, the bed-elevation regime is dominated by sediment supplydriven fluctuations in bedload transport occurring at timescales shorter than the seasonal fluctuation in discharge. The study also indicates that bed-elevation monitoring on Squamish River, and others like it, for purposes of detecting and measuring aggradation/degradation must take into account very considerable and normal channel-bed variability operating at timescales from hours to months.