Progradation and termination of subaerial river-dominated delta networks

Abstract:

Delta networks are ubiquitous on Earth and extraplanetary surfaces. Their ramification structure shares great similarities with other physical realms like lightning, drainage networks, bacteria growth and viscous fingering. Recent study by Ke et al. (2019) showed the geomorphic evolution of delta network, like aforementioned systems, can be described by the moving boundary method, governed by the Laplacian equation. Expanding on that, here we show that the progradation rate of subaerial delta networks can be quantified by a simple, theoretical equation that takes into account the water and sediment discharge, network topology, channel geometry and substrate resistance. The formulation and the associated physical picture indicate that as the prograding channels continue to bifurcate, the water discharge in each channel decays and progradation rate vanishes. The vanishing of progradation rate thus sets the condition for the termination of coeval delta growth, which is hypothesized to lead to establishments of a new protruding lobe or a channel avulsion. Our theoretical formulation therefore predicts both the progradation rate of delta networks at each time frame and their termination conditions as the progradation rate vanishes. The predictions of theoretical formulation are tested well against numerical model results and real-world delta networks. Since the major varied factor among all that govern the networks growth is the climatically-controlled water discharge, this work thus has the potential to link records of delta network growth to climate fingerprint.

Reference:

Ke, W.-T., J. B. Shaw, R. C. Mahon, and C. A. Cathcart (2019), Distributary Channel Networks as Moving Boundaries: Causes and Morphodynamic Effects, Journal of Geophysical Research: Earth Surface, 124. 1878– 1898, doi:10.1029/2019jf005084.