Essential Site Maintenance: Authorea-powered sites will be updated circa 15:00-17:00 Eastern on Tuesday 5 November.
There should be no interruption to normal services, but please contact us at [email protected] in case you face any issues.

loading page

Exploring Sediment Compaction in Experimental Deltas: towards a meso-scale understanding of coastal subsidence patterns
  • +3
  • Samuel M Zapp,
  • Kelly Marie Sanks,
  • Jose Silvestre,
  • John Shaw,
  • Ripul Dutt,
  • Kyle Martin Straub
Samuel M Zapp
Louisiana State University

Corresponding Author:[email protected]

Author Profile
Kelly Marie Sanks
Tulane University
Author Profile
Jose Silvestre
Tulane University
Author Profile
John Shaw
University of Arkansas at Fayetteville
Author Profile
Ripul Dutt
Tulane University
Author Profile
Kyle Martin Straub
Tulane University
Author Profile

Abstract

We present the first investigation of subsidence due to sediment compaction and consolidation in two laboratory-scale river delta experiments. Spatial and temporal trends in subsidence rates in the experimental setting may elucidate behavior which cannot be directly observed at sufficiently long timescales, except for in reduced scale models such as the ones studied. We compare subsidence between a control experiment using steady boundary conditions, and an otherwise identical experiment which has been treated with a proxy for highly compressible marsh deposits. Both experiments have non-negligible compactional subsidence rates across the delta-top, comparable in magnitude to our boundary condition relative sea level rise of 250 μm/h. Subsidence in the control experiment (on average 54 μm/h) is concentrated in the lowest elevation (<10mm above sea level) areas near the coast and is likely due to creep induced by a rising water table near the shoreface. The treatment experiment exhibits larger (on average 126 μm/h) and more spatially variable subsidence rates controlled mostly by compaction of recent marsh deposits within one channel depth (_10 mm) of the sediment surface. These rates compare favorably with _eld and modeling based subsidence measurements both in relative magnitude and location. We find that subsidence “hot spots” may be relatively ephemeral on longer timescales, but average subsidence across the entire delta can be variable even at our shortest measurement window. This suggests that subsidence rates in a given decade or century may exceed thresholds for marsh platform drowning, even if the long term trend does not.