Abstract
The morphologies of the world’s deltas are thought to be determined by river discharge, tidal range and wave action 1. More recently, sea-level rise 2,3 and human engineering4 have been shown to shape delta evolution. The effects of factors such as sediment type and the overall amount of sediment carried by rivers are considered secondary4,5,6. In particular, the role of sediment cohesion, which is controlled by sediment size and type of vegetation, is unclear. Here we use a numerical flow and transport model7,8,9,10 to show that sediment cohesiveness also strongly influences the morphology of deltas. We find that, holding all other factors constant, highly cohesive sediments form bird’s-foot deltas with rugose shorelines and highly complex floodplains, whereas less cohesive sediments result in fan-like deltas with smooth shorelines and flat floodplains. In our simulations, sediment cohesiveness also controls the number of channels that form within the deltas, and the average angle of bifurcation of those channels. As vegetation generally acts as a cohesive agent, we suggest that deltas that formed before the expansion of land plants in the Devonian period should show fan-like characteristics, a finding consistent with the limited data from the sedimentological record11.
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Change history
20 January 2010
In the version of this Letter initially published online, the cell size given in the second paragraph of the Methods should have been 625 m2. This error has been corrected in all versions of the text.
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Acknowledgements
The authors would like to acknowledge financial support from NSF grant EAR-0809653, and the Donors of the American Chemical Society Petroleum Research Fund for support of this research. D.A.E. was supported by the STC Program of the National Science Foundation through the National Center for Earth-Surface Dynamics under agreement EAR-0120914. We thank D. Hoyal, B. Sheets and G. Parker for discussions about deltas and cohesion. The focus of this manuscript greatly benefited from reviews by J. Syvitski and D. Jerolmack.
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D.A.E. designed and conducted the numerical modelling and analyses. D.A.E. and R.L.S. critically analysed the results and wrote the paper.
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Edmonds, D., Slingerland, R. Significant effect of sediment cohesion on delta morphology. Nature Geosci 3, 105–109 (2010). https://doi.org/10.1038/ngeo730
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DOI: https://doi.org/10.1038/ngeo730
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