the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 11 Mar 2026
Sediment storage and routing in bedrock canyons
Abstract. Bedrock river bathymetry is dynamic, with incision rates dependent on sediment cover, supply, and mobility in the channel. However, the scale and fluctuation of this dynamic sediment storage is not well understood, particularly in large bedrock rivers where the bed is not visible at low flows. We used repeat, high resolution, multibeam bathymetric surveys from 2021–2023 to characterize bed and bank topography in nine bedrock canyons that are representative of a wide range of width, depth, slope, and velocity observed through the 375 km long Fraser Canyon in British Columbia. Change in elevation as high as 15 m is identified between surveys. We characterize patches of contiguous change to measure changes in sediment storage volume. Our observations reveal that channel morphology determines where storage occurs. We find that sediment is 'staged' through canyons, initially being deposited in a canyon near a sediment supply site, then moving downstream as the initial deposit declines. Substantial changes in storage volume occur without substantial changes in patch footprint. These findings provide key context for interpreting the reach-scale structure of bedrock erosion, the long-term evolution of mountain river networks, and the moderation of sediment delivery to lowland environments.
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Status: final response (author comments only)
- RC1: 'Comment on egusphere-2026-819', Stefanie Tofelde, 30 Apr 2026
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RC2: 'Comment on egusphere-2026-819', Anonymous Referee #2, 21 May 2026
This paper uses a dataset of repeat bathymetric surveys along canyons of the Fraser River to explore variability of sediment erosion, deposition and storage and link this to canyon morphology and a sediment input event. I found this a very interesting paper – it is an amazing set of data! We do often make a lot of assumptions in models and calculations around bedload cover and storage, so it is really valuable to have data on this, particularly from a large river with variable morphology. The treatment and presentation of the data does a good job illustrating and synthesizing a large amount of complex change data. The interpretations are interesting and follow clearly from the data. I found the story on sediment staging particularly interesting. I don’t have any major concerns, just some very minor points below, although I do agree with the other reviewer that some discussion about implications for modeling would be a great addition.
Line 125: Can you add the gauging station to the map in figure 2?
Line 140: Lytton is also not on the map
Line 170: 2022 is only April, not May?
Line 205: it would be good to specify here that you mean the minimum elevation at each pixel. I know you have this a few lines down, but the sentence as it is may give readers the wrong idea at first.
Line 252: absolute value of the mean of each patch?
Line 254: in line 204, it says that the smallest patch size considered was 2 m2, and here it says 12 m2, is that because no patches between 2-12 m2 were observed?
Line 272-3: this repeats what you already said in line 266
Citation: https://doi.org/10.5194/egusphere-2026-819-RC2
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General comments
In the study “Sediment Storage and Routing in Bedrock Canyons,” Ross et al. employ repeat high-resolution multibeam bathymetric surveys (2021–2023) to examine morphological changes across nine reaches of the Fraser Canyon, British Columbia, following a major sediment supply event in 2021. Based on four survey campaigns, they quantify spatial and temporal variations in sediment erosion and deposition, including changes in patch size, distribution, and volume. Their results highlight highly dynamic sediment behavior, with deposits exhibiting merging, splitting, and alternating phases of erosion and accumulation.
This contribution is based on a case study, and it successfully captures the highly dynamic behaviour characteristic of natural fluvial systems. The authors maintain a clear and well-structured presentation throughout, which is particularly commendable given the complexity of the dataset, including varying survey durations and differences among study reaches. Overall, the manuscript is very well organized and easy to follow.
The text is clearly written, and the figures are of high quality and effectively support the analysis. The study represents a valuable contribution to the field and provides a strong foundation for future model development (see specific comment below). Beyond one main point raised below and a number of minor technical corrections, I have no major concerns.
Specific comments
It would strengthen the discussion to include a dedicated section—potentially at the end of the discussion or following lines 437–438, where this issue is briefly raised—addressing the broader implications of this case study for modeling sediment transport and long-profile evolution of bedrock rivers. The observations presented here underscore a clear mismatch between the complex, highly dynamic nature of sediment routing documented in the field and the simplified process representations commonly employed in current numerical models, which are often unable, or only partially able, to reproduce such behaviour. In particular, the observed patterns of transient storage, patch-scale dynamics, and episodic sediment release indicate that sediment transport is more spatially and temporally heterogeneous than is typically assumed. Explicitly acknowledging this discrepancy would provide valuable context for interpreting the results and help define key priorities for future model development, including improved representation of localized sediment storage, non-linear transport processes, and event-driven system responses to better capture river morphological evolution.
Technical corrections
Figure 1: In (a) it might help to add a label of sideview and topview. In (b), (d), and (f) please add a scale bar for reference.
Figure 2: Please add an inset map indicating the study location within Canada. In panel (b), geographic coordinates are missing, which prevents subsequent georeferencing and should therefore be included. Additionally, the legend in panel (b) should clarify that the values represent upstream river kilometers; alternatively, the flow direction could be indicated with an arrow for clarity.
Figure 3 caption: Spelling mistake, should be ERA1 instead of ERA2 for the 2022 freshet.
Figure 6a: Maybe add another number to the x-axis for better orientation. In the figure caption, add a comma before ‘(b) area…’.
I wish you all the best with the revision, and I apologize for the delay in providing my comments.