Computational Modelling Group

The Origin of Aeolian Dunes (TOAD)

Starting
1st June 2018
Ending
31st May 2021
Investigators
Joanna Nield

A Conceptual model of interactions between form, flow and transport relevant to dune initiation and development (after Best, 1993). B Five conceptual stages of dune development (Kocurek et al., 1992) with Stage 2 Namibian example

TOAD is a jointly funded NERC-NSF Standard Grant with investigators Dr Jo Nield (Southampton), Prof Giles Wiggs (Oxford), Dr Matthew Baddock (Loughborough), Prof Jim Best (Illinois, US) and Prof Ken Christensen (Notre Dame, US) and project partners Prof Gary Kocurek (UT-Austin), Prof Nick Lancaster (Desert Research Institute USA), Dr Serina Diniega (JPL, CalTech), Dr William Anderson (UT-Dallas), Prof Philippe Claudin (CRNS, Paris), Andrew Valdez (Great Sand Dunes National Park, Colorado), Dr Gillian Maggs-Kölling (Gobabeb Research and Training Centre, Namibia), Dr Martin Hipondoka (University of Namibia), Caroline Hern (Shell International) and the Royal Geographical Society (RGS).

Aeolian (wind-blown) sand dunes occupy 10% of the Earth’s surface, both in vast desert sand seas and as important natural defences against flooding along coasts. While the environmental conditions that influence the shape, movement and patterns of fully grown dunes have been extensively studied, arguably the most enduring deficiency in our understanding of these landforms is also the most profound: how do wind-blown dunes initiate?

Initiation is central to understanding dunes as major geological units, including the response of these landscapes to climatic drivers, environmental change and societal impact. The significance of dune initiation for the wider understanding of wind-blown sandy systems and their contexts, for which the discovery of extra-terrestrial dune fields has added a recent impetus, ensures that the question of initiation has remained prominent throughout the history of desert research. Despite this, existing ideas proposed to explain processes of dune origin have remained largely descriptive and uncorroborated. The persistence of the question regarding dune initiation is not due to an absence of appreciation of its importance but, rather, a lack of the means to tackle this fundamental issue.

The critical obstacle to a fully developed understanding of dune initiation is that, until now, measurement of the necessary variables, at the ultra-high spatial and temporal resolutions required to detect small-scale variations in surface conditions and wind-blown sand transport, has been impossible. Recent technological advances in the geosciences both inspire and underpin this proposal, as they now provide the opportunity to meet the demanding requirements of process measurement.

Surmounting the abiding problem of dune initiation requires novel approaches in research design and our proposal tackles the issues of measurement at small scales by forging complementary links between fieldwork and physical modelling, as well as an ability to widen the application of detailed process findings through computer modelling. Specifically, this proposal will for the first time examine the key inter-relationships between airflow, surface properties, changes in sand transport and bedform shape that lie behind a meaningful understanding of how nascent dunes emerge. Full measurement of controlling processes and bedform development will be achieved through field monitoring of surface properties and bedform change at extremely high resolution. A key novelty of the fieldwork is that it will be carried out at three carefully chosen locations of known dune development, with each location representing the ‘type site’ for three different drivers of dune initiation; surface roughness, surface moisture and sand bed instability.

The fieldwork will inform experiments undertaken in a bespoke laboratory flume that is designed to enable accurate characterisation of flow very close to the 3D surface of modelled dunes using state-of-the-art imaging techniques. Our field and laboratory dataset will be used to drive a computer model that we will then run to test the sensitivity of dune initiation and growth to different controls in a range of environmental conditions in deserts, coasts and on other planets.

Our proposal is built on a new capability to make field observations at the requisite exceptional levels of detail, augmented by closely coupled state-of-the-art laboratory flow simulations, plus the development and application of evidence-based modelling to examine drivers of dune initiation. In concert, this approach represents an unprecedented opportunity to overcome a truly enduring plateau for understanding the origins of one of the major terrestrial landform systems.

For more background information on protodunes and the techniques that we will use to study them, see:

  • Baddock, M.C., Nield, J.M., Wiggs, G,F.S. (2017) Early-stage aeolian protodunes: bedform development and sand transport dynamics. Earth Surface Processes and Landforms, doi: 10.1002/esp.4242.

  • Nield, J.M., Wiggs, G,F.S., Baddock, M.C., Hipondoka, M.H.T. (2017) Coupling leeside grainfall to avalanche characteristics in aeolian dune dynamics, Geology, 45(3): 271-274, doi: 10.1130/G38800.1.

  • Nield, J.M., Wiggs, G.F.S. and Squirrell, R.S. (2011) Aeolian sand strip mobility and protodune development on a drying beach: examining surface moisture and surface roughness patterns measured by terrestrial laser scanning, Earth Surface Processes and Landforms, 36(4): 513-522, doi: 10.1002/esp.2071.

  • Nield, J.M. and Wiggs, G.F.S. (2011) The application of terrestrial laser scanning to aeolian saltation cloud measurement and its response to changing surface moisture. Earth Surface Processes and Landforms, 36(2): 273–278, doi: 10.1002/esp.2102.

Categories

Physical Systems and Engineering simulation: CFD, Earth Observation, Earth surface dynamics, Fluid Dynamics, Landscape evolution, Sediment transport, Turbulence

Algorithms and computational methods: Cellular automata

Programming languages and libraries: C, Matlab

Computational platforms: Iridis