Groundwater affects the geomorphic and hydrologic properties of coevolved landscapes
Journal Article
Overview
abstract
The hydrologic dynamics and geomorphic evolution of watersheds are; intimately coupled – runoff generation and water storage are controlled; by topography and properties of the surface and subsurface, while also; affecting the evolution of those properties over geologic time. However,; the large disparity between their timescales has made it difficult to; examine interdependent controls on emergent hydro-geomorphic properties,; such as hillslope length, drainage density, extent of surface; saturation. In this study, we develop a new model coupling hydrology and; landscape evolution to explore how runoff generation affects long-term; catchment evolution, and analyze numerical results using a; nondimensional scaling framework. We focus on hydrologic processes; dominating in humid climates where storm runoff primarily arises from; shallow subsurface flow and from precipitation on saturated areas. The; model solves hydraulic groundwater equations to predict the water table; location given prescribed, constant groundwater recharge. Water in; excess of the subsurface capacity for transport becomes overland flow,; which generates shear stress on the surface and may detach and transport; sediment. This affects the landscape form that in turn affects runoff; generation. We show that (1) three dimensionless parameters describe the; possible steady state landscapes that coevolve under steady recharge;; (2) hillslope length increases with increasing transmissivity relative; to the recharge rate; (3) three topographic metrics—steepness index,; Laplacian curvature, and topographic index—provide a basis to recover; key model parameters from topography (including subsurface; transmissivity). These results open possibilities for topographic; analysis of humid upland landscapes that could inform quantitative; understanding of hydrological processes at the landscape scale.
