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First order controls of avulsion in river deltas
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  • Octria Adi Prasojo,
  • Trevor B. Hoey,
  • Amanda Owen,
  • Richard David Williams
Octria Adi Prasojo
University of Glasgow

Corresponding Author:octria.prasojo@glasgow.ac.uk

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Trevor B. Hoey
Brunel University London
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Amanda Owen
University of Glasgow
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Richard David Williams
University of Glasgow
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Changed hydrological regimes, sea-level rise, and accelerated subsidence are all putting river deltas at risk across the globe. Deltas may respond to these stressors through the mechanism of avulsion. Decades of delta avulsion studies have resulted in conflicting hypotheses that avulsion frequency and location are upstream (water and sediment discharge) or downstream (backwater and sea-level rise) controlled. In this study, we use Delft3D morphodynamic simulations to investigate the main controls over delta avulsion. Avulsion timing and location were recorded in six scenarios modelled over a 400-year period with varying alluvial slopes upstream of a delta slope break (1.13x10-4 to 3.04x10-3) within a range representative global deltas. We measure several independent morphometric variables including avulsion length, delta lobe width, channel width at avulsion, delta topset slope and sediment load. Correlating these variables with the avulsion timescales observed in our model shows that avulsion timescale is mostly controlled by sediment load, which in turn is controlled by the alluvial slope upstream of a delta slope break. With higher stream power index in steeper alluvial slopes, more sediment can be carried within a channel, resulting in more frequent avulsions. Our results are consistent with the avulsion timescale derived from an analytical solution, 19 natural deltas and downscaled physical laboratory deltas. These results help mitigate delta avulsion risk by focusing management efforts on variables that primarily control avulsion in a river delta, but also induce further debate over whether sea-level rise may, or may not, trigger more avulsions in river deltas.
12 Sep 2023Submitted to ESS Open Archive
13 Sep 2023Published in ESS Open Archive