Channel connectivity in estuarine environments

The channel patterns in estuaries vary from simple, single-thread systems to highly complex networks. Thus, developing quantitative connections between process and these highly variable channel network structures is an enticing challenge for geomorphologists. In this presentation, we use spectral graph theory to analyze structural and dynamical connectivity of estuarine channel networks extracted from satellite imagery. The selected estuaries vary in spatial scale and range from classic alluvial systems to delta-like branching networks. For comparison, we develop a set of schematic networks representing endmembers of estuarine channel patterns. Analyses of connectivity in the schematic networks are used to contextualize the results from estuaries around the world. The results reveal that estuaries often carry the mutually evasive flood and ebb channel signature, but also contain branching structures associated with deltas or converging tidal patterns, especially in larger systems. As systems become larger, branching and looping structures become more prevalent, leading to higher value of structural connectivity indices. Flow direction is shown to be a major control on dynamical connectivity with flow being more localized in the ebb direction and is linked to channel depth distributions in both real-world and numerically modeled estuaries. This work provides a benchmark for understanding the connections among flux allocation, flow direction, and channel network structure in estuaries.