COMPARING AND CONTRASTING TRIBUTARY AND DISTRIBUTARY CHANNEL NETWORKS (Invited Presentation)

Rivers accumulate water and sediment through tributary channel networks and disperse them through distributary channel networks. The structure and dynamics of these networks have important implications for engineering, prediction and stratigraphic interpretation. For both tributary and distributary networks, a key geomorphic transition separates channelized and unchannelized flow. We explore similarities and differences between this transition in tributary and distributary settings that control the growth and structure of the resulting network. One key similarity is that unchannelized flow may occur as diffusion within the unchannelized domain in both tributary and distributary settings. Modeling shows that this diffusion can control both channel branching and channel elongation within a network. This flow pattern produces an emergent mean bifurcation angle of 72° that is consistent with several tributary and distributary field settings, including in seismically imaged ancient distributary networks. One key difference concerns the geometry of drainage area in tributary networks compared to the nourishment area of distribuary networks: drainage areas are generally nested within a network making tributary networks fractal over a wide range of scales. In contrast, the nourishment area of a distributary channel must extend into the basin and cannot be nested, and therefore the fractal does not theoretically apply in the same way. Using modeling and a sedimentological case study, we show the utility of comparative analysis of tributary and distributary networks.