Hydro‐geomorphic metrics for high resolution fluvial landscape analysis

Thomas Bernard (1) , Philippe Davy (1) , Dimitri Lague (1, 2)

1 GR - Géosciences Rennes
2 OSUR - Observatoire des Sciences de l'Univers de Rennes

Topographic metrics are designed to quantify scale-relevant relationships between geometric properties of landscapes to reveal the processes shaping them. They have long been derived from topographic flow routing algorithms, initially developed for coarse Digital Elevation Models (DEMs), whose resolution (≥ 30 m) and poor precision did not resolve correctly flow patterns and channel flow width. Since high resolution and precision DEMs make the description of meter-scale flow patterns possible, new methods are required to analyze high resolution landforms structures such as hillslope-channel connections, channel width or floodplains. Here, we investigate the potential of 2D hydraulic simulations based on the shallow water equations to replace the classical slope vs drainage area analysis, to analyse river morphology and to identify floodplains. We apply the Floodos model to the 1 m resolution DEM of the Elder Creek catchment, California, from which we derive three hydro-geomorphic metrics accounting for the river geometry: a specific drainage area extended to channels, an effective flow width and the hydraulic slope. We analyse the Elder Creek catchment through what we call the hydraulic slope-area diagram allowing a better identification of hillslope-channel connections than the slope-area approach. The effective flow width is analyzed along the drainage network and is characterized by a power-law relationship consistent with previous observations. We derive metrics based on a multi-runoff approach to automatically identify floodplains and evaluate along-stream variations in hydraulic geometry. The hydro-geomorphic metrics offer a geomorphic analysis suitable for high resolution DEMs and opens up new perspectives in fluvial landscape analysis.

Domaines: Géomorphologie

Thomas Bernard, Philippe Davy, Dimitri Lague. Hydro‐geomorphic metrics for high resolution fluvial landscape analysis. Journal of Geophysical Research: Earth Surface, 2022, 127 (3), pp.e2021JF006535. ⟨10.1029/2021JF006535⟩. ⟨insu-03607941v2⟩