A study finds that sea-level rise and subsidence, which can drown river deltas, can also drive the phenomenon of river avulsion, in which rivers rapidly change course. River avulsions are responsible for delta growth and coastal land-building through sediment deposition, but they also present catastrophic flood risks. Austin J. Chadwick and colleagues used field data and modeling to examine how sea-level rise and subsidence affect river avulsions on deltas. Investigating the timing of river avulsions, the authors found that the frequency is related to the rate of sea-level rise, the rate of subsidence, and the supply of sediment that drives delta growth. The balance of the rates also determines whether a delta advances or retreats. For most deltas, the authors found, modern rates of sea-level rise and subsidence should cause more frequent river avulsions. In extreme cases with low sediment supply, avulsions will also occur farther inland, presenting hazards to upstream communities. According to the authors, engineered avulsions can help mitigate climate change effects; however, thresholds still exist beyond which sediment supply is unable to keep up with rising sea level, shifting avulsion hazards upstream.
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Article #19-12351: "Accelerated river avulsion frequency on lowland deltas due to sea-level rise," by Austin J. Chadwick, Michael P. Lamb, and Vamsi Ganti.
MEDIA CONTACT: Austin J. Chadwick, California Institute of Technology, Pasadena, CA; e-mail: <achadwick@caltech.edu>
Journal
Proceedings of the National Academy of Sciences