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Accelerated river avulsion frequency on lowland deltas due to sea-level rise

Chadwick, Austin J. and Lamb, Michael P. and Ganti, Vamsi (2020) Accelerated river avulsion frequency on lowland deltas due to sea-level rise. Proceedings of the National Academy of Sciences of the United States of America, 117 (30). pp. 17584-17590. ISSN 0027-8424. PMCID PMC7395564. doi:10.1073/pnas.1912351117.

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Sea-level rise, subsidence, and reduced fluvial sediment supply are causing river deltas to drown worldwide, affecting ecosystems and billions of people. Abrupt changes in river course, called avulsions, naturally nourish sinking land with sediment; however, they also create catastrophic flood hazards. Existing observations and models conflict on whether the occurrence of avulsions will change due to relative sea-level rise, hampering the ability to forecast delta response to global climate change. Here, we combined theory, numerical modeling, and field observations to develop a mechanistic framework to predict avulsion frequency on deltas with multiple self-formed lobes that scale with backwater hydrodynamics. Results show that avulsion frequency is controlled by the competition between relative sea-level rise and sediment supply that drives lobe progradation. We find that most large deltas are experiencing sufficiently low progradation rates such that relative sea-level rise enhances aggradation rates—accelerating avulsion frequency and associated hazards compared to preindustrial conditions. Some deltas may face even greater risk; if relative sea-level rise significantly outpaces sediment supply, then avulsion frequency is maximized, delta plains drown, and avulsion locations shift inland, posing new hazards to upstream communities. Results indicate that managed deltas can support more frequent engineered avulsions to recover sinking land; however, there is a threshold beyond which coastal land will be lost, and mitigation efforts should shift upstream.

Item Type:Article
Related URLs:
URLURL TypeDescription Information CentralArticle
Chadwick, Austin J.0000-0002-2552-0083
Lamb, Michael P.0000-0002-5701-0504
Ganti, Vamsi0000-0003-2165-6052
Additional Information:© 2020 National Academy of Sciences. Published under the PNAS license. Edited by Andrea Rinaldo, École Polytechnique Fédérale de Lausanne, Lausanne, Switzerland, and approved June 3, 2020 (received for review July 17, 2019). PNAS first published July 13, 2020. We thank Andrew Moodie, Gary Parker, Jeffrey Nittrouer, Hongbo Ma, and Brad Murray for useful discussions and three reviewers for constructive comments. We acknowledge NSF Grant EAR 1427262 and the Resnick Sustainability Institute at the California Institute of Technology for support. Author contributions: A.J.C., M.P.L., and V.G. designed research; A.J.C. and M.P.L. performed research; A.J.C. and M.P.L. analyzed data; and A.J.C., M.P.L., and V.G. wrote the paper. The authors declare no competing interest. This article is a PNAS Direct Submission. Data deposition: The data and model code underlying this study are publicly available in the SEAD Repository ( and GitHub (, respectively. This article contains supporting information online at
Group:Resnick Sustainability Institute
Funding AgencyGrant Number
Resnick Sustainability InstituteUNSPECIFIED
Subject Keywords:sea-level rise; river deltas; river avulsion
Issue or Number:30
PubMed Central ID:PMC7395564
Record Number:CaltechAUTHORS:20200714-092850643
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Official Citation:Accelerated river avulsion frequency on lowland deltas due to sea-level rise. Austin J. Chadwick, Michael P. Lamb, Vamsi Ganti. Proceedings of the National Academy of Sciences Jul 2020, 117 (30) 17584-17590; DOI: 10.1073/pnas.1912351117
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:104373
Deposited By: Tony Diaz
Deposited On:14 Jul 2020 16:41
Last Modified:16 Nov 2021 18:31

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