Evaluating Divide Migration Distances Using Vestiges of Prior Drainage Networks: Insight from Modeling and Application to the Dadeldhura Klippe, Western Nepal

Changes in topographic relief and elevation accomplished through drainage reorganization contribute uncertainty to studies of landscape evolution and often require inferring paleo-topography from indirect information. While the literature is rich with techniques for assessing the stability of modern divides and regional applications of these techniques, fewer topography-centric studies have focused on evaluating paleo-divide locations. Here, we address this challenge by exploring how vestiges of initial drainage networks preserved upstream of stream capture events might be used to infer migration paths of drainage divides. We present findings from numerical simulations in which a change in boundary conditions results in the overprinting of an initial drainage network into a new drainage network such that stream captures cause dramatic shifts in flow direction. Results show how fluvial and hillslope measurements (e.g., junction angles, flow direction, channel steepness, and hillslope aspect) upstream of stream capture events evolve throughout model runs. We compare these measurements to those of tributaries from a control modeled landscape that evolves with fixed boundary conditions. Using these results, we discuss which properties of the initial drainage network are best preserved in the new drainage network and contrast most with those from the control experiment. Findings from simulations are then applied to the southern margin of the Dadeldhura klippe in western Nepal, where satellite imagery and topographic analyses suggest ongoing northward divide migration and degradation of a low-relief surface in the southern Himalaya fold and thrust belt.