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Channel adjustment in a small mountain stream over a long flood series : insights from the morphological method

University of British Columbia

The use of high-resolution topographical data (HRTD) with the morphological method has largely remained restricted to active channels with high sediment transport regimes, where disturbance is significantly higher than noise within HRTD, yet channels with low stream orders and low sediment transport regimes dominate watersheds. The morphological method with HRTD was used to determine spatial and temporal trends of channel adjustment in East Creek, a small gravel-bed channel with a low sediment transport regime near the Coast Mountains of British Columbia, over a fifteen-year flood series. A probabilistic threshold with 68% confidence intervals was used to determine distributions of significant bed elevation change in conjunction with a tracer data set, and these disturbance distributions were compared between different morphologies. These distributions were then used to determine the volumetric input from the bed to the net morphological displacement (NMD), a new term proposed to distinguish the net processes that occur after multiple events from bed material transport. Cross-sectional surveys were used to determine the NMD fraction originating from the channel banks since HRTD cannot capture undercutting. The disturbance distributions are best described by the log-normal distribution, although the distribution tails tend to deviate from the log-normal. These distributions were found to generally be statistically similar between the different morphologies within both depositional and erosional areas. Erosion from the bed was found to generally become more significant to the NMD relative to erosion from the banks going downstream, and both the NMD and mean disturbance depths were found to not be correlated with the hydrological conditions. This lack of correlation may be best explained by the channel history. The disturbance distributions and their volumes found from HRTD were compared to the same determined from tracer stone surveys and cross-sectional surveys, respectively, both more traditional surveys. The distributions found from HRTD were found to result in more robust estimations that can be studied at increased spatial levels than from those found using tracer stones alone, and disturbance volumes from cross-sections were found to differ from those found using HRTD by a maximum and minimum of six and one-sixth times.

Text

2021-04-20

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/77840

Geography

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/