EGU2020-182
https://doi.org/10.5194/egusphere-egu2020-182
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Proto-dune formation under a bimodal wind regime

Pauline Delorme1, Giles Wiggs2, Matthew Baddock3, Joanna Nield1, James Best4, Kenneth Christensen5, Nathaniel Bristow5, Andrew Valdez6, and Philippe Claudin7
Pauline Delorme et al.
  • 1School of Geography and Environmental Science, University of Southampton, Southampton, UK (p.m.t.delorme@soton.ac.uk)
  • 2School of Geography and the Environment, University of Oxfrod, Oxford, UK
  • 3Geography and Environment, Loughborough University, Loughborough, UK
  • 4Departement of Geology, University of Illinois at Urbana-Champaign, Champaign, Illinois, USA
  • 5Department of Aerospace and Mechanical Engineering, University of Notre Dame, Notre Dame, Indiana, USA
  • 6National Park Service - NPS - Great Sand Dunes National Park & Preserve, Mosca, Colorado, USA
  • 7Laboratoire de Physique et Mecanique des Milieux Heterogenes, ESPCI - CNRS - PSL Research University – Univ.Paris-Diderot – Sorbonne Universite, Paris, France

Early-stage aeolian bedforms develop into sand dunes through complex interactions between flow, sediment transport and surface topography. Depending on the specific environmental and wind conditions the mechanisms of dune formation, and ultimately the shape of the nascent dunes, may differ. Here, we investigate the formation of a proto-dune-field, located in the Great Sand Dunes National Park ( Colorado, USA), using a three dimensional linear stability analysis.

We use in-situ measurements of wind and sediment transport, collected during a one-month field campaign, as part of a linear stability analysis to predict the orientation and wavelength of the proto-dunes.

We find that the output of the linear stability analysis compares well to high-resolution Digital Elevation Models measured using terrestrial laser scanning. Our findings suggest that the bed instability mechanism is a good predictor of proto-dune development on sandy surfaces with a bimodal wind regime.

How to cite: Delorme, P., Wiggs, G., Baddock, M., Nield, J., Best, J., Christensen, K., Bristow, N., Valdez, A., and Claudin, P.: Proto-dune formation under a bimodal wind regime, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-182, https://doi.org/10.5194/egusphere-egu2020-182, 2019

Comments on the presentation

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Presentation version 3 – uploaded on 30 Apr 2020
few correction
  • CC1: Comment on EGU2020-182, Nathalie Vriend, 04 May 2020

    Hi Pauline,

    I have a few questions on your presentation:

    * Is it correct that you assume that Q is constant for all different wind directions? What happens if the sand source is directional as well, with e.g. more Q in winds from the SW, and less Q in winds from the S. Can you compensate for that in your model?

    * Reading further, it seems that you are differentiating Q in wind direction. However, I am still unsure when you deduce Q from the wind measurements, or whether you measure Q with your Sensit with an angle dependency? Is your measured sediment motion directional, or accumulative?

    * Your measured dune wavelength, orientation and growth rate have a fantastic overlap with your prediction (well done!), but the celerity is underestimated. You do not provide a specific explanation for this. Can you hypothesize what factors impact your celerity prediction, what could cause this discrepancy?

     

    All best,

    Nathalie (from Cambridge)

    • AC1: Reply to CC1, Pauline Delorme, 04 May 2020

      Hi Nathalie, 

       

      * The sediment flux is calculated from the wind velocity for each direction, using a quadratic transport law. The conversion from Sensit measurement to sediment flux is calibrated, in order to check the validity of our transport law. 

      *Concerning the sand source, as the protodune form on an erodible bed the sand source is multidirectional, the sand that constructs the dune comes from the bed. 

      *The celerity is the value the most dependent to the sediment flux, so one possible explanation is that we underestimate the sediment flux. 

       

      I hope this answer yours questions. 

       

      All best, 

      Pauline 

  • CC2: Comment on EGU2020-182, Andrew Gunn, 04 May 2020

    Hi Pauline!

    Great job, glad to see these field observations worked out nicely. 

    Can you explain the choice of A and B in your linear stability analysis please?

    All the best,

    Andrew

    • AC2: Reply to CC2, Pauline Delorme, 04 May 2020

      Hi Andrew, 

      A and B are very difficult to meassure in the field. So for this study I took, A and B ranging respectively from [3.5 , 4] and [1.5, 2] according to Charru et al. ,2013 and Claudin et al., 2013.

      Best, 

      Pauline

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