Exploring the interaction between rivers and sand dunes : implications for fluvial-aeolian geomorphology

Liu, Baoli (Environmental scientist)

Geography
September 2014

Thesis or dissertation


Rights
© 2014 Baoli Liu. All rights reserved. No part of this publication may be reproduced without the written permission of the copyright holder.
Abstract

The interaction between fluvial and aeolian processes can significantly influence landforms. When rivers and sand dunes meet, the interaction of sediment transport between the two systems can lead to change in either one or both systems. However, these two systems are usually studied independently which leaves many questions unresolved in terms of how they interact. This study investigated interactions between fluvial and aeolian processes, focusing on the triggers that switch the dominance between one process and the other, and the consequent changes in geomorphology that may occur.

Firstly, a global inventory of fluvial-aeolian interactions at 230 globally distributed locations was collected using satellite imagery. At each site, the following attributes were measured: net sand transport direction, fluvial-aeolian meeting angle, dune type and river channel pattern. From these data, six different types of interaction were classified that reflect a shift in dominance between the fluvial and aeolian systems. Results from this classification confirm that only certain types of interaction were significant: the meeting angle and dune type, the meeting angle and interaction type and finally the channel pattern and interaction type. These results show the importance of fluvial – aeolian interactions, but also reveal the difficulties of understanding dynamic geomorphic systems from images taken at a single moment in time.

A highly novel cellular fluvial and aeolian/dune model was then developed to simulate the process interactions over longer periods of time. Results from the global inventory were used to set up the computational domain and different flow regimes (perennial and ephemeral) were simulated interacting with different magnitudes of aeolian sand transport. The model results demonstrated the same six types of interaction that were identified in the global survey, and also provided a better understanding of the dynamics of landform change which cannot be interpreted from single ‘snapshot’ images. In perennial fluvial systems, when the ratio between fluvial discharge (Rs) and aeolian sand transport rate (Dc) was in a range of critical values, the landscape exhibited cyclic behaviour with abrupt large-scale changes in the absence of external forcing. River channels would avulse around dunes significantly altering the river/dune configuration and affecting sediment output. The interaction types observed in the modelled scenarios also exhibited transient characteristic with gradual or rapid shifts between various interaction types even under stable conditions. In contrast, landform evolution in ephemeral fluvial systems was very different from perennial environments. Dunes crossed the river channel more easily in ephemeral environments and channel development was more irregular with wetland areas developing and frequent changes in channel pattern. The results suggest that the duration of the wet season is more important than the timing of the wet season on the sediment output rates.

This study has demonstrated the importance of fluvial-aeolian interactions for understanding landform development in certain fluvial-aeolian environments and has shown that these systems may show complex responses even with constant input conditions.

Publisher
Department of Geography, Environment and Earth Sciences, The University of Hull
Supervisor
Coulthard, Tom J.; McLelland, S. J.(Stuart J.)
Sponsor (Organisation)
University of Hull; China Scholarship Council
Qualification level
Doctoral
Qualification name
PhD
Language
English
Extent
8 MB
Identifier
hull:12301
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