Optimal conditions for floodplain sedimentation and land aggradation in river deltas

Abstract

Crevasse splays are landforms created by breaching of river levees and are part of many large river systems over the world. Due to potentially high aggradation rates, they can be effective tools against relative sea level rise. Here we describe a combined field- and modeling effort, in which we assessed the effects of floodplain drainage on crevasse splay development. By mapping crevasse splays for the Rhine-Meuse- and Mississippi Deltas and linking it to floodplain size, we investigated the effect of the floodplain on crevasse formation. We used the morphodynamic model Delft3D-FLOW to test results found in the field. We found that the largest floodplains accommodate the largest crevasse splays. This was confirmed by our model simulations, in which simulations with large floodplains have slowly rising water levels, keeping lateral surface slopes high which ultimately result in large flow velocities and rapid crevasse growth. Additionally, we found that small flood durations increase erosion and thus further aid this effect. The combined effect of flood duration and floodplain size were combined into a parameter, which was proven to accurately predict crevasse growth in the model and allows for a first order comparison with field data. The conclusions drawn from this research increase our understanding in crevasse growth and my help in future restoration projects that involve artificial levee breaching