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Earth Surface Dynamics An interactive open-access journal of the European Geosciences Union
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Discussion papers
https://doi.org/10.5194/esurf-2019-12
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/esurf-2019-12
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 20 Mar 2019

Research article | 20 Mar 2019

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

A global delta dataset and the environmental variables that predict delta formation

Rebecca L. Caldwell1,2, Douglas A. Edmonds1, Sarah Baumgardner2,3, Chris Paola3, Samapriya Roy4, and Jaap H. Nienhuis5 Rebecca L. Caldwell et al.
  • 1Department of Earth and Atmospheric Sciences, Indiana University, Bloomington, IN, 47401, USA
  • 2Chevron Energy Technology Company, Chevron Corporation, Houston, TX, 77005, USA
  • 3Department of Earth Sciences, University of Minnesota, Minneapolis, MN, 55455, USA
  • 4Department of Geography, Indiana University, Bloomington, IN, 47401, USA
  • 5Department of Physical Geography, Utrecht University, Utrecht, the Netherlands

Abstract. River deltas are sites of sediment accumulation along the coastline that form critical biological habitats, host megacities, and contain significant quantities of hydrocarbons. Despite their importance, we do not know which factors most significantly promote sediment accumulation and dominate delta formation. To investigate this issue, we present a global dataset of 5,399 coastal rivers and data on eight environmental variables. Of these rivers, 40 % (n = 2,174 deltas) have geomorphic deltas, defined either by a protrusion from the regional shoreline, a distributary channel network, or both. Globally, coastlines average one delta for every ~ 300 km of shoreline, but there are hotspots of delta formation. For example, in Southeast Asia there is one delta per 100 km of shoreline. Our analysis shows that the likelihood of a river to form a delta increases with increasing water discharge, sediment discharge, and drainage basin area. On the other hand, delta likelihood decreases with increasing wave height and tidal range. Delta likelihood has a non-monotonic relationship with receiving basin slope: it decreases with steeper slopes but increases for slopes > 0.006. This relationship likely reflects different controls on delta formation on active versus passive margins. Sediment concentration and recent sea-level change do not affect delta likelihood. A logistic regression shows that water discharge, sediment discharge, wave height, and tidal range are most important for delta formation. The logistic regression correctly predicts delta formation 75 % of the time. Our global analysis illustrates that delta formation and morphology represent a balance between constructive and destructive forces, and this framework may help predict tipping points where deltas rapidly shift morphologies.

Rebecca L. Caldwell et al.
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Short summary
River deltas are valuable resources that support biodiversity and human habitation. Despite this we do not have a global census of deltas nor do we know the conditions that promote their formation. We surveyed 5,399 river mouths greater than 50 m wide and found that 2,174 (40 %) create a delta. The conditions that lead to delta formation are high sediment input and low wave and tide conditions. These results can be used to understand how deltas will adapt to environmental changes.
River deltas are valuable resources that support biodiversity and human habitation. Despite this...
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