Growth laws for channel networks incised by groundwater flow

Abstract

Groundwater seepage is expected to affect channel features, but its role remains controversial. Two linear response relationships that describe channel evolution from groundwater flux are sufficient to characterize seepage-driven channel networks, linking the dynamics of channel growth to channel morphology. The re-emergence of groundwater at the surface shapes the Earth’s topography through a process known as seepage erosion1,2,3,4,5. In combination with flow over land6, seepage erosion contributes to the initiation and growth of channel networks1,2,3,4,5. Seepage processes have also been invoked in the formation of enigmatic amphitheatre-headed channel networks on both Earth7,8,9,10,11 and Mars12,13,14. However, the role of seepage in producing such channels remains controversial11,15,16. One proposed growth law for channel development suggests that the velocity at which channel heads advance is proportional to the flux of groundwater to the heads17. Here we use field observations and physical theory to show that this simple model, combined with a second linear response that relates channel branching to the total groundwater flux to the network, is sufficient to characterize key aspects of the growth and form of a kilometre-scale seepage-driven channel network in Florida18. We find that the dynamics for the advance of channel heads are reversible, which allows us to estimate the age of the channel network and reconstruct the history of its growth. Our theory also predicts the evolution of the characteristic length scale between channels19, thereby linking network growth dynamics to geometric form.