Medium-Detail Delta Morphodynamic Modeling: Initial Experiments with Avulsion Behaviors, Sediment Delivery, Artificial Leeves, and Relative Sea Level Rise Rates

Abstract:

Deltas and their flat, fertile lands have become the most densely populated places on earth, but, partly because of anthropogenic interactions with fluvial, coastal, and wetland processes, their inhabitants are increasingly susceptible to natural disasters. Humans have decreased sediment supply delivered to rivers and ultimately wetlands and the coast, causing accelerating subsidence. The natural course and processes of many rivers have been altered through channelization, artificial levees, and dams, which ‘perch’ the river above its floodplain. As the rate of relative sea-level rise (RSLR) increases, so will surface aggradation and channel backfilling, resulting in a fluvial system that is more vulnerable to flooding and frequent avulsions. To investigate the effects of increasing RSLR and anthropogenic manipulations on delta morphodynamics, we create new avulsion and floodplain modules to couple with the 3D mode of Sedflux (Hutton and Syvitski, 2008), a stratigraphic basin-filling model. We replace the probabilistic approach of channel avulsion previously used in the model with a module incorporating the steepest-decent methodology used in Jerolmack and Paola (2007), and a floodplain algorithm to deposit sediment on subaerial cells. Model experiments with Sedflux and the new modules address the effects on delta morphodynamics of varying rates of RSLR (affecting base-level), changes in sediment delivery (adjusting the upstream boundary conditions), and restriction of natural fluvial dynamics (inhibiting avulsions). The work presented here is the first step in a more expansive project to develop a new 3D eco-morphodynamic delta model system that will be based on further model couplings, including a vegetation module (that will affect fluvial and floodplain dynamics) and a coastline module (that will re-work the shoreline based on wave-driven alongshore sediment transport). The model system results will be tested and calibrated based on comparisons with observations from both the field and physical experiments.

Hutton, E, and J Syvitski (2008), Sedflux 2.0: An advanced process-response model that generates three-dimensional stratigraphy, Comput. Geosci. 34(10) 1319-1337.

Jerolmack, D, and C Paola (2007), Complexity in a cellular model of river avulsion, Geomorphology 91(3), 259-270.