Hydrological Connectivity Controls Magnitude and Distribution of Sediment Deposition Within the Deltaic Islands of Wax Lake Delta, LA, USA
2021
Olliver, E. A. | Edmonds, D. A.
Relative sea‐level rise in the coming century will increase the risk of flooding and shoreline retreat on most major river deltas. River deltas can counteract flooding and shoreline retreat by depositing sediment on their surface. Yet, it is unclear what processes influence sedimentation and its variability on deltaic surfaces. Towards this end, we conducted a numerical modeling study in Delft3D to understand how floods, tides, and vegetation affect sedimentation rates and their spatial variability on islands in a deltaic system. Our experiments use a fully calibrated and validated hydrodynamic model of Wax Lake Delta, LA, USA. We analyzed eight numerical experiments that include a control simulation with no floods, tides, or vegetation, and seven simulations where we add in floods, tides, and vegetation. Our results clearly show that floods and tides have opposing effects. Compared to the control, floods introduce more sediment and increase the mean sedimentation rate, whereas, tides spread sediment over a larger area and decrease the mean sedimentation rate. Vegetation has a negligible effect on mean sedimentation rates but does shift sedimentation closer to the shoreline and to higher elevations. Overall, the amount of sedimentation on an island depends on its hydrological connectivity with the surrounding distributary channels. These results show that hydrologically well‐connected deltaic islands subject to tidal and riverine flooding aggrade their surfaces more evenly, which may be ideal for preventing inundation from relative sea‐level rise.
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