Topographic and Stratigraphic Expressions of Floodplain Morphodynamics

Understanding the intricate relationship between channels and their floodplains is essential for estimating how rivers networks will respond to changing land-use and climate and for understanding stratigraphic architecture in alluvial basins. Conventional advection-diffusion models, though widely used, oversimplify the complex interplay of factors governing floodplain dynamics. Here we explore the degree to which floodplain topography reflects synchronous channel-floodplain coupling in a variety of alluvial basins and consider how this these conditions are recorded in the stratigraphic record of ancient river networks. Using a combination of Landsat, Sentinel, and Radar imagery and ICESat-2 data from river basins from different tectonic and climatic settings, we mapped floodplain morpho-dynamic and topographic features including levees, floodplain channels, floodplain lakes, crevasse-splay lobes, and crevasse channels. We compared the shape, scale, and spatial arrangement of these features to each other and to simplified, scaled geometric models of floodplain topography arising from processes like channel lateral migration, channel avulsion, floodplain erosion, crevasse-splay deposition, and spatially randomized floodplain compaction. These observations provide a basis for comparing the degree to which spatial topographic and hydrologic features on floodplains reflect active channel-floodplain coupling or a relict floodplain state. We apply this insight to examples from the ancient stratigraphic record where features like floodplain lakes, crevasse-splay deposition, and floodplain incision can be observed in the context of the scale, polynomiality, and paleo-avulsion behavior of associated ancient channels. This work provides a new approach to assessing the nature of channel-floodplain coupling in modern and ancient rivers.