Conceptual basis and operational guidance for inferring drainage divide migration and river capture using topographic data

Abstract

Drainage divide migration and river capture reorganise drainage networks by redistributing drainage area between adjacent basins, thereby altering water and sediment fluxes, patterns of fluvial incision, and ecological connectivity. Computational advances have made it routine to derive landscape-scale topographic metrics that are commonly used to suggest divide instability and drainage reorganisation. This operational ease, however, has not been matched by a detailed conceptual-operational guide that makes explicit the underlying assumptions, limitations, and best practices. Here, I provide a roadmap to infer divide mobility and discrete capture events from topography. I first introduce the χ integral transformation and key practical decisions for its use, including extensions for spatially variable uplift and effective erodibility and the link between χ and fluvial response times. I then outline a workflow to infer likely divide mobility from cross-divide χ contrasts between adjacent basins and complementary hillslope-asymmetry metrics, emphasising internal consistency checks and sensitivity tests. Finally, I develop an evidence-based logic for diagnosing discrete captures centred on topographic archives that record past connectivity, especially windgaps and valley-scale inherited geometry. I show how these archives can be quantified and how to evaluate alternative controls (regional transients driven by changes in tectonics, lithology, and climate) to reduce false positives. I conclude by outlining minimum reporting standards and operational recommendations.