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Abstract

Surface water level, river discharge and water storage change are sensible indicators of long-term change of water cycle within a river catchment. Recently, low water levels in the river Rhine made navigation difficult, while high water levels due to intense rain events caused serious losts. In this work, we compute river discharge from space observations using simple equation including the parameters water height, river slope and river width. The first two are from SAR nadir altimetry over 2016-2023 and the last from imagery. The fluvial characteristics is first investigated in a preliminary analysis. The river width changes less during the year and changes in heights and slope are relevant. Mean discharge is computed from 17 in-situ stations. The key first-order hydraulic parameters, i.e. channel bathymetry and Manning’s roughness coefficient are not measurable from space. The river depth is from a DTM and the Manning’s coefficient from a least square adjustment at 17 in-situ stations rating curve. The method is applied to Virtual Gauge (VG) where slope is computed. The river discharge at the stations is evaluated against Sobek hydrodynamic model and against GR4J model, a catchment water balance model that relates runoff to rainfall and evapotranspiration. Lastly, we compare nadir and simulated SWOT in the cal/val phase. SWOT will give the parameters water height, river slope and river width, but without real data a simulation uses the Sobek model as input to the CNES Hydrology Simulator. Finally, we compare temporal and spatial discharge from nadir and swath- data in same interval and region.