Morphological evolution of bifurcations in tide-influenced deltas [post]

Arya P. Iwantoro, Maarten van der Vegt, Maarten G. Kleinhans
2019 unpublished
<p><strong>Abstract.</strong> 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
more » ... orphodynamic 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.</p>
doi:10.5194/esurf-2019-63 fatcat:qjxuih2kxjdsllqm2v5utmgfn4