Systematic valley floor extraction for characterizing valley width distribution in mountain landscapes : comparison between hydraulic and geometrical approaches

Lurin, Aude; Steer, Philippe; Clubb, Fiona; Gailleton, Boris

doi:10.5194/egusphere-2026-3145

Preprints

https://doi.org/10.5194/egusphere-2026-3145

Preprints

15 Jun 2026

| 15 Jun 2026

Systematic valley floor extraction for characterizing valley width distribution in mountain landscapes : comparison between hydraulic and geometrical approaches

Aude Lurin, Philippe Steer, Fiona Clubb, and Boris Gailleton

Abstract. Valleys are key elements of mountainous landscapes, governing the transfer of water and sediment while recording the influence of tectonic and climatic forcing. Despite their importance, the quantitative characterization of valley morphology at large spatial scales remains challenging, particularly due to limitations in automated extraction methods. In this study, we compare two approaches for delineating valley extent from digital elevation models: a classical geometrical method based on topographic thresholds, and a novel pseudo-hydraulic method that estimates flood-prone areas using a simplified water-filling algorithm. Using 30 m resolution DEMs, we find that both perform well and that the conceptual difference between them is mainly significant in headwater areas. We then find that the main control on valley width is drainage area, consistent with previous work. The use of a wideness index allows us to identify local deviations from the width–area scaling, highlighting secondary controls such as lithological changes. New insights into valley morphology could be obtained through the large-scale systematic extraction of valleys across various tectonic and climatic settings.

Received: 01 Jun 2026 – Discussion started: 15 Jun 2026

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Aude Lurin, Philippe Steer, Fiona Clubb, and Boris Gailleton

Status: final response (author comments only)

RC1:
'Comment on egusphere-2026-3145', Anonymous Referee #1, 07 Sep 2026
This manuscript investigates two automated tools for quantifying valley width and tests them in far-flung field study area to deduce systematic trends in valley width as well as factors that cause valley width to deviate from these trends. The authors develop a novel, flood-based algorithm that uses a hydraulic-like approach and compare it to a geometric approach previously developed and published by the authors. They test these algorithms using geologic maps of alluvial deposits and use a statistical approach to assess performance. Their findings confirm previous studies showing how valley width tends to scale with drainage area and they also show how tectonics, glacial history, and bedrock affects valley width. The wideness index is a clever and useful tool that has much promise. The manuscript is generally well-written with thorough scholarship and novel observations. The manuscript is very well-suited for ESURF and should be published after some minor revisions detailed below.
The text has a raft of minor grammatical and spelling issues that should be corrected (see below). These issues did not detract from the flow and comprehension of the text but they demand attention. In addition, the text often had paragraphs in odd places whereby the flow was interrupted. Again, a very minor but sometimes confusing issue that's readily remedied.

The figures are generally well constructed and highly illustrative but they frequently lack important information, such as panel numbers, scale, north arrows, and legends that would greatly improve their clarity and accessibility. Can the authors revisit each figure and ensure that these are included? Also, the captions should be more descriptive, referring to the different panels, etc.

The abstract finishes with a rather vanilla statement about new insights. I strongly encourage the authors to finish with a more compelling and specific statement about the utility and potential impact of these tools and insights.

In the introduction, the valley defining approaches are described briefly but can the authors more clearly describe the rationale for one method vs. the other? the approaches are presented without much context.

The choice of defining valley width below the headwaters has implications for interpreting divide migration, feedbacks with hillslope processes and lots more interesting questions (section 2.1). The rationale for this choice could be more compelling and less arbitrary. Can the authors draw upon previous papers, such as May et al 2013, that defines valleys into the headwaters? what is gained/lost by this choice and can the authors present an analysis showing why 5 km^2 is a meaningful scale to start their method?

the methods section is devoid of units for the quantities. can the authors populate the appropriate units throughout?

The method uses 30-m DEM data but the sensitivity of the results to this choice is not addressed.

The use of the F1 score to assess model accuracy is a good choice but can the authors express why they made this choice? There are a multitude of ways to splice up the confusion matrix to generate metrics depending on the relative importance of false negatives and false positives. What is the objective for this test in terms of what to minimize/maximize?

figure 6: the western alps fits (left side) are highly influenced by one outlier bin at high drainage area that causes the fits to have much higher exponents. an alternative regression scheme could be considered given that the remainder of the data set has a very well-defined trend. This would put less emphasis on the apparently high exponent in this field area, which seems to be driven by a singular bin value.

on figure 6, the point density and binned points have similar color schemes and it was difficult to decipher them. Can the authors more clearly differentiate the bins vs. density data? perhaps make the used and not-used bins (black and gray)?

minor comments:
line 39: "first" appears, but "second" does not. Also, this would be better structured as one paragraph.
line 53: these "other controls" are relatively unsatisfying. can the authors explain a bit more about how these processes feedback on valley width and how it may affect observed trends?
line 55: do the authors mean "channel" profiles? the vast lectures on tectonic geomorph focuses on channel profiles.
line 137-9: incomplete sentence and inconsistent structure. rewrite for clarity.
line 297: "that" not "the"
line 344-6: refer to the figures that show these trends.
line 380-6: make one paragraph.
line 392: distributions
line 396-7: the choice and method of separating up and down stream valleys with a 300m threshold is not clear. how does this work? please refer to a figure and show what's being done. also, is this choice driven by the scottish highlands? can this be more systematic?
Citation: https://doi.org/10.5194/egusphere-2026-3145-RC1
RC2:
'Comment on egusphere-2026-3145', Anonymous Referee #2, 05 Oct 2026
The manuscript introduces a new method for automated valley floor delineation and compares its results with those of an existing approach in 4 selected regions that are distinctly different. To this end, mapped extents of alluvial deposits in geologic maps are used as benchmark data. Finally, the valley width results are discussed in the regional geological context, and end-member classifications for valley types are proposed. The main findings demonstrate the applicability of the new approach, while the discussion nicely highlights the differences between the two approaches. Furthermore, the results confirm that valley width appears to scale primarily with drainage area, whereas glacial history, tectonic structure, and bedrock type may have a much smaller effect.
The manuscript is well written and logically structured. The methods are well introduced and easy to follow, and the results are clear and convincing. The study is well within the scope of Earth Surface Dynamics, and I have only a few minor suggestions for improvement (see below and the attached inline comments). Congratulations to the authors on this nice study!

Minor comments:
The introduction could do with more focus in some parts (see related in-line comments). The rationale behind the new valley-width extraction method and the reasons for choosing the 4 selected regions could be expanded.

The geologic datasets could be better referenced, and some figure captions could be improved (see also related in-line comments).

Some text in the result section might better fit in the discussion and/or the setting chapter (see related in-line comments).

Panel numbering and specific references would better link the figures to the text.

Figure 3: More details on the binning of the data for the thresholds would be helpful. Furthermore, in the Pyrenean foothills, larger values might yield even higher F1 scores (see also inline comments).

In Figure 6, the fit for the western Alps seems to be influenced by the binning (as also pointed out by reviewer 1; see also in-line comments). Maybe testing a different binning could lead to a more robust fit?

A few more comments on wording, on some typos, and occasionally on the text structure can be found in the in-line comments.
Citation: https://doi.org/10.5194/egusphere-2026-3145-RC2

Aude Lurin, Philippe Steer, Fiona Clubb, and Boris Gailleton

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Short summary

The dynamics of mountains landscapes is controled by their valley networks. The morphology of valleys, including their width, impacts how they transmit sediments and water and record tectonic or climatic signals. In order to further our understanding of the controls of valley morphology and width, we compare two automatic valley extraction methods in four regions. We then evaluate how valley width and morphology is affected dy drainage area, lithology, and the tectonic and geomorphic setting.


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