Nourishment Area Asymmetry Relates A Distributary Channel Network's Structure and Dynamics

Deltas and their associated distributary channels are complex networks. A nourishment area is defined as the area which is nourished by water and sediment from a given channel cross section. Understanding the connection between nourishment area and asymmetrical partitioning of discharge and sediment transport at a bifurcation is critical for understanding the geomorphological evolution of deltaic systems. A distributary channel network's structure constrains nourishment area geometry. At a channel bifurcation, we hypothesize that asymmetry in daughter nourishment areas acts as a control upon the partitioning asymmetry of discharge and sediment, thereby influencing delta dynamics. Using Sentinel 2 imagery of the Wax Lake Delta in Louisiana, acquired concurrent to the fieldwork, channel widths and nourishment areas were calculated in ArcMap. Discharges were measured by doing 4 transects across each parent and daughter channel of 13 asymmetrical bifurcations using a Teledyne Riverpro ADCP. Suspended sediment concentrations were measured by taking 3 depth integrated point samples at the thalweg of each channel. Data show width asymmetry having a range of 1-10, nourishment area asymmetry (large daughter divided by small daughter) having a range of 1-50, and asymmetrical partitioning of discharge and sediment having a range of 1-100. Power law functions relate the asymmetry ratios of width to discharge, nourishment area to discharge, and width to nourishment area. Regression analysis shows that 78 percent of discharge asymmetries and 74 percent of width asymmetries can be explained by nourishment area asymmetries. These results imply that asymmetries in nourishment areas are a control upon the partitioning of discharge. This provides a link between a channel network's structure and dynamics and indicates that the dynamics of an individual distributary channel cannot be considered independently from its neighboring channels.