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.