Weathering-Permeability Feedback Controls on Lateral Flow Partitioning and the Weathering Front Advance Rate

Abstract:

Weathering rates depend upon water fluxes through the weathering zone in transport-controlled systems. Conversely, water flux rates through the weathering zone depend upon hydraulic conductivity and pore space generated by weathering. This balance, along with topographic gradient and overall hillslope relief, also affects the partitioning of water laterally along the hillslope. This interdependent feedback loop between weathering and vertical and lateral hydraulic fluxes could result in a pattern of coevolution that may determine regolith structure. Most current models of regolith advance fail to explicitly account for lateral movement of water out of the weathering column. Here we present an exploration of this feedback and its consequences using a simple one-dimensional model that incorporates partitioning to lateral flow. An analytical solution is presented for an elementary linear feedback, and more complex feedbacks are explored numerically. The model predicts water table and weathering front geometry based upon slope and regolith properties, and suggests that this feedback may have consequences for the weathering front advance rate, baseflow transit time distributions, and concentration discharge relations. Understanding the feedback loops that produce regolith structure and flow paths at a hillslope scale will provide insights into the critical zone structural controls.