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Abstract Rising sea levels, subsidence, and decreased fluvial sediment load threaten river deltas and their wetlands. However, the feedbacks between fluvial and non‐fluvial (marsh) deposition remain weakly constrained. We investigate how non‐riverine, elevation‐controlled deposition typified by marshes impacts sediment partitioning between a delta's topset, coastal zone, and foreset by comparing a delta experiment with proxy marsh accumulation to a control. Marsh accumulation alters fluvial sediment distribution by decreasing the slope in the marsh window by ∼50%, creating a 78% larger marsh zone. Fluvial incursions into the marsh window trap 1.3 times more clastic volume. The volume exported to deep water remains unchanged. Marsh deposition shifts elevation distributions toward sea level, which produces a hypsometry akin to field‐scale deltas. The elevation‐lowering effect of marshes on an equilibrium delta shown here constitutes an unexplored feedback and an important aspect of coastal sustainability.
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Marsh-induced backwater: the influence of non-fluvial sedimentation on a delta's channel morphology and kinematics
Abstract. We investigate the interaction of fluvial and non-fluvial sedimentation on the channel morphology and kinematics of an experimental river delta. We compare two deltas: one that evolved with a proxy for non-fluvial (“marsh”) sedimentation (treatment experiment) and one that evolved without the proxy (control). We show that the addition of the non-fluvial sediment proxy alters the delta's channel morphology and kinematics. Notably, the flow outside the channels is significantly reduced in the treatment experiment, and the channels are deeper (as a function of radial distance from the source) and longer. We also find that both the control and treatment channels narrow as they approach the shoreline, though the narrowing is more pronounced in the control compared to the treatment. Interestingly, the channel beds in the treatment experiment often exist below sea level in the terrestrial portion of the delta top, creating a ∼ 0.7 m reach of steady, non-uniform backwater flow. However, in the control experiment, the channel beds generally exist at or above relative sea level, creating channel movement resembling morphodynamic backwater kinematics and topographic flow expansions. Differences between channel and far-field aggradation produce a longer channel in-filling timescale for the treatment compared to the control, suggesting that the channel avulsions triggered by a peak in channel sedimentation occur less frequently in the treatment experiment. Despite this difference, the basin-wide timescale of lateral channel mobility remains similar. Ultimately, non-fluvial sedimentation on the delta top plays a key role in the channel morphology and kinematics of an experimental river delta, producing channels which are more analogous to channels in global river deltas and which cannot be produced solely by increasing cohesion in an experimental river delta.
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- PAR ID:
- 10493321
- Publisher / Repository:
- Copernicus
- Date Published:
- Journal Name:
- Earth Surface Dynamics
- Volume:
- 11
- Issue:
- 6
- ISSN:
- 2196-632X
- Page Range / eLocation ID:
- 1035 to 1060
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.5194/esurf-11-1035-2023
