Landscape ‘stress’ and reorganization from χ-maps: Insights from experimental drainage networks in oblique collision setting

Abstract

Several recent studies have suggested that maps of flow length normalized for drainage area called chi (χ) could reveal landscapes in a transient state, which are prone to reorganizations of basin geometry, flow line topology and water divide locations. However, the potentially long timescales associated with the evolution of basin geometry make the capability of χ to predict such reorganization challenging to test in natural settings. Here, we investigate the evolution of experimental drainage networks developed on a wedge coupled to a piedmont and growing in oblique convergence. We use this experimental setting to investigate the relationships between χ maps, the imposed tectonic deformation and the drainage network evolution. As deposition can occur within channels or in the piedmont, our experimental streams deviate from purely bedrock channels for which the χ metric has been initially developed. Yet we show that the large-scale χ pattern of the experimental drainage network is consistent with the imposed deformation field, as ∼2/3 of the observed χ gradients across water divide are oriented in the expected direction with respect to the imposed deformation. This suggests that χ maps can be used to infer the horizontal component of regional deformation in large-scale natural mountainous fluvial landscapes. In addition, we observe that when a divide affected by a χ gradient migrates, the orientation of the gradient correctly anticipates the sense of landscape reorganization for ∼2/3 of these divides. © 2018 John Wiley & Sons, Ltd.