Presentation by LDEO postdoc Austin Chadwick
Title:
How do river deltas respond to relative sea-level rise?
Abstract:
River deltas are currently sinking due to the combination of sea-level rise and land subsidence,
endangering roughly half a billion people worldwide. Under threat of drowning, river deltas
naturally fight back by building new land through sediment deposition. Most estimates of delta
response are based on sustainability of the entire delta; however, deposition and land loss can
vary spatially because coastal rivers undergo catastrophic changes in course, known as river
avulsions, that shift the distribution of water and sediment. Here I present field observations,
numerical simulations, and laboratory experiments to develop the first mechanistic framework
for delta response to relative sea-level rise that accounts for river avulsion processes. Numerical
and experimental data are in agreement with field observations, showing that avulsions
preferentially occur at a location and frequency set by the hydrodynamics of lowland rivers.
Results indicate that, for most densely populated deltas, modern rise will drive more frequent
river avulsions and flood hazards. With anticipated increases to sea-level rise in the coming
century, shorelines and avulsion sites are expected to shift inland, introducing new hazards to
upstream communities. Applied to land-management problems, this framework shows
maintaining modern delta area through the century will require more sediment than previously
estimated.
