Draining the fluvial battery through groundwater and surface flow: energy partitioning and fluvial landscape evolution

All widely used fluvial landscape evolution models rely on a power-law scaling between discharge and drainage area. In settings with relatively high relief and low permeability, this assumption is often sufficient to capture landscape-scale fluvial dynamics and migration of drainage divides. What happens to geomorphic dynamics when those assumptions break down?  For example, carbonate karst systems can move massive amounts of water through the subsurface, sometimes against local topographic gradients. To address this question, we introduce a framework for landscape evolution based on the dissipation of the potential energy of precipitation as it takes both surface and subsurface flow paths. We demonstrate the utility of this framework by comparing the widely used “streampower plus diffusion” landscape evolution model with one in which water can take flow paths both over the surface and through the subsurface, responding to groundwater hydraulic head gradients. The framework explains how large carbonate plateaus like the Swabian Alb in southern Germany can persist and stall drainage capture despite a massive river profile asymmetry between Rhine and Danube catchments. Finally, we suggest that in such layered rock systems, the combination of contrasts in lithologic strength and permeability are primary controls on landscape evolution.