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Discussion papers
https://doi.org/10.5194/esurf-2019-63
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/esurf-2019-63
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 28 Nov 2019

Submitted as: research article | 28 Nov 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Earth Surface Dynamics (ESurf).

Morphological evolution of bifurcations in tide-influenced deltas

Arya P. Iwantoro, Maarten van der Vegt, and Maarten G. Kleinhans Arya P. Iwantoro et al.
  • Department of Physical Geography, Faculty of Geosciences, Utrecht University, Utrecht, 3508 TC, the Netherlands

Abstract. In river-dominated deltas, bifurcations often develop an asymmetrical morphology, i.e. one of the downstream channels silts up while the other becomes the dominant one. In tide-influenced systems, bifurcations are thought to be less asymmetric and both downstream channels of the bifurcation remain open. The main aim of this study is to understand how tides influence the morphological development of bifurcations. By using a 2DH morphodynamic model (Delft3D), we simulated the morphological development of tide-influenced bifurcations on millennial time scales. The schematized bifurcation consists of an upstream channel forced by river discharge and two downstream channels forced by tides. Two different cases were examined. In the first case, the downstream channels started with unequal depth or length but had equal tidal forcing, while in the second case the morphology was initially symmetric but the downstream channels were forced with unequal tides. Furthermore, we studied the sensitivity of results to the relative role of river flow and tides. We find that with increasing influence of tides over river, the morphology of the downstream channels becomes less asymmetric. Increasing tidal influence can be achieved by either reduced river flow with respect to the tidal flow, or by asymmetrical tidal forcing of the downstream channels. The main reason for this behaviour is that tidal flows tend to be less unequal than river flows when geometry is asymmetric. For increasing tidal influence, this causes less asymmetric sediment mobility and therefore transport in both downstream channels. Furthermore, our results show that bedload tends to divide less asymmetrical compared to suspended load, showing a possible stabilizing effect of lateral bed slopes on morphological evolution. In our simulations, the more tide-dominated systems tend to have a larger ratio of bedload and suspended load transport. Our results explain why distributary channel networks deltas with strong tidal influence are more stable than river-dominated ones.

Arya P. Iwantoro et al.
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Arya P. Iwantoro et al.
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Short summary
We investigated the effect of tides on morphodynamic evolution of bifurcations in tide-influenced deltas. Using results from a numerical morphodynamic model (Delft3D), we found that tides cause less asymmetric bifurcations, and thereby keep both downstream channels to open. Our results explain why avulsion rarely occurs in tide-influenced deltas, whereas it occurs more often in river-dominated deltas.
We investigated the effect of tides on morphodynamic evolution of bifurcations in...
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