When Does Faulting‐Induced Subsidence Drive Distributary Network Reorganization?

Deltas exhibit spatially and temporally variable subsidence, including vertical displacement due to movement along fault planes. Faulting‐induced subsidence perturbs delta‐surface gradients, potentially causing distributary networks to shift sediment dispersal within the landscape. Sediment dispersal restricted to part of the landscape could hinder billion‐dollar investments aiming to restore delta land, making faulting‐induced subsidence a potentially significant, yet unconstrained hazard to these projects. In this study, we modeled a range of displacement events in disparate deltaic environments, and observe that a channelized connection with the displaced area determines whether a distributary network reorganizes. When this connection exists, the magnitude of distributary network reorganization is predicted by a ratio relating dimensions of faulting‐induced subsidence and channel geometry. We use this ratio to extend results to real‐world deltas and assess hazards to deltaic‐land building projects. Plain Language Summary Coastal deltaic landscapes globally are losing area due to rising sea level and land subsidence. Billions of dollars in river diversions are planned on several deltas globally, intended to offset land loss by directing sediment necessary to sustain coastal land to areas experiencing land loss. Success of these projects depends on widespread sediment dispersal, distributed via extensive channel networks emerging from diversion sites. But, the possibility for rapid faulting‐induced subsidence to restrict channel networks and limit land building has not been adequately considered in diversion planning. Here, we present numerical simulations that show how faulting‐induced subsidence impacts sediment dispersal, and how this informs hazards present to planned Mississippi River delta sediment diversions. Key Points Faulting‐induced subsidence reorganizes distributary networks, ephemerally restricting sediment dispersal and slowing land building Reorganization timing and style depend on self‐organized avulsion style, and scale with a dimensionless displacement magnitude Faulting‐induced subsidence presents an under‐constrained hazard to land‐building sediment diversions