How 2D Hydraulic Modelling Can Improve Landscape Analysis in Tectonic Geomorphology?

International audienceThe channel network has long been studied as an active marker of spatial variations in tectonic uplift rates. River profiles are also analysed to uncover past tectonic or climatic perturbations. High Resolution LiDAR DEM (HRDEM, 30 m) cannot offer. This increased resolution and precision is expected to yield better detection of subtle topographic signals and identification of catchment domains. But it also requires new methods to address the significant change in resolution. Here, we apply a 2D hydraulic modelling at catchment scale to revisit and go beyond the traditional set of tools developed for coarse DEM analysis.Several methods using topographic features such as curvature, slope-area relationship or Chi-analysis, have been developed during the last decades to extract channel head and channel characteristics. Yet, these methods use flow routing (D8 or D-inf) that are not consistent with HRDEM analysis of channels wider than several pixels. Moreover, high local slope variation from HRDEM can introduce biases in topographic analysis which is classically reduced by filling and erosion procedures. Moreover, these methods only scratch the potential of HRDEM to describe a more complete set of channel characteristics such as channel width.To overcome the classical flow routing limitations, we apply the 2D hydraulic model Floodos, based on the 2d shallow water approximation, on 2m LiDAR DEM catchments located in the San Gabriel Mountains and Angelo reserve in California. By filling the channels, the hydraulic model fully account for channel width variations in the calculation of hydraulic parameters (hydraulic slope, bed shear stress, flow velocity). We introduce a new geomorphic descriptor the hydraulic slope – discharge relationship that has several benefits over the classical slope-area relationship: our results show a sharper transition between the colluvial and fluvial domain as well as a much clearer expression of the power law scaling in the fluvial domain. In addition, we introduce new hydro-geomorphic descriptors such as the shear stress-discharge relationship which shows promising results for channel head detection and river morphology analysis in the context of tectonic geomorphology