Delta allometry: Growth laws for river deltas

Under projected scenarios of sea‐level rise, subsidence, and sediment starvation many deltas around the world are expected to drown. Delta growth dynamics, which determine the ability of a delta to adapt to these changes, are poorly understood due to the difficulty of measuring change in slowly evolving landscapes. We use time‐series imagery of experimental, numerical, and field‐scale deltas to derive four laws that govern the growth of river‐dominated deltas. Land area grows at a constant rate in the absence of relative sea level change, while wetted area keeps pace, maintaining a constant wetted fraction over the delta surface. Scaling of edge‐lengths versus areas suggests delta shorelines are nonfractal, even though the channel network is fractal. Consequently channel‐edge length, which provides critical habitat, grows more rapidly than delta area. These laws provide a blueprint for delta growth that will aid in delta restoration and help predict how existing deltas will evolve.