Effective channel and ungauged braided river discharge estimation by assimilation of multi-satellite water heights of different spatial sparsity

P.-A. Garambois (1, 2) , Kévin Larnier (2) , Jerome Monnier (3) , Pascal Finaud-Guyot (2) , Jonas Verley (3) , Amanda Samine Montazem (4, 2, 5) , Stephane Calmant (4, 5)

1 INSA Strasbourg - Institut National des Sciences Appliquées - Strasbourg
2 ICube - Laboratoire des sciences de l'ingénieur, de l'informatique et de l'imagerie
3 IMT - Institut de Mathématiques de Toulouse UMR5219
4 LEGOS - Laboratoire d'études en Géophysique et océanographie spatiales
5 UT3 - Université Toulouse III - Paul Sabatier

Multi-satellite sensing of continental water surfaces (WS) represents an unprecedented and increasing potential for studying ungauged hydrological and hydraulic processes from their signatures, especially on complex ow zones such as multichannel rivers. However the estimation of discharge from WS observations only is a very challenging inverse problem due to unknown bathymetry and friction in ungauged rivers, measurements nature, quality and spatio-temporal resolutions regarding the flow (model) scales. This paper proposes an effective hydraulic modeling approach of sufficient complexity to describe braided river flows from sparse multisatellite observations using the HiVDI inverse method presented in Larnier et al. [42] with an augmented control vector including a spatially distributed friction law depending on ow depth. It is shown on 71km of the Xingu River (braided, Amazon basin) with altimetric water height time series that a fairly accurate upstream discharge hydrograph and effective patterns of channel bathymetry and friction can be infered simultaneously. The coherence between the sparse observation grid and the ne hydraulic model grid is ensured in the optimization process by imposing a piecewise linear bathymetry prole b(x), which is consistent with the hydraulic visibility of WS signatures (Garambois et al. [27], Montazem et al. [46]). The discharge hydrograph and effective bathymetry-friction patterns are retrieved from 8 years of satellite altimetry (ENVISAT) at 6 virtual stations (VS) along flow. Next, the potential of the forthcoming SWOT data, dense in space, is highlighted by infering a discharge hydrograph and dense patterns of effective river bathymetry and friction; a physically consistent definition of friction by reaches enabling to consider more dense bathymetry controls. Finally a numerical analysis of the friction term shows clear signatures of river bottom slope break in low flows and width variations in high flows which is consistent with the findings of Montazem et al. [46] from WS curvature analysis.

Mots clés: Multichannel River; Ungauged River; 1D Hydraulic Model; Data Assimilation; Satellite Altimetry; SWOT; Hydraulic Visibility

Domaines: Analyse numérique [math.NA]; Sciences de l'environnement; Environnement et Société; Sciences de l'ingénieur [physics]

P.-A. Garambois, Kévin Larnier, Jerome Monnier, Pascal Finaud-Guyot, Jonas Verley, et al.. Effective channel and ungauged braided river discharge estimation by assimilation of multi-satellite water heights of different spatial sparsity. 2019. ⟨hal-02308560⟩