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| Titel |
Uncertainty quantification in hydrodynamics bidimensional models : the case of Gironde estuary forecast model |
| VerfasserIn |
Vanessya Laborie, Nicole Goutal, Sophie Ricci, Philippe Sergent |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250137559
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| Publikation (Nr.) |
 EGU/EGU2017-312.pdf |
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| Zusammenfassung |
| In the context of the development and the implementation of data assimilation techniques in
Gironde estuary for flood forecasting, a Telemac 2D model is used to calculate water depths
and velocity fields at each node of an unstructured mesh. Upstream, the model boundaries are
respectively La Réole and Pessac on the Garonne and Dordogne river. The maritime
boundary is 32 km off the mouth of Gironde estuary, located in Verdon. This model, which
contains 7351 nodes and 12838 finite elements, does not take into account overflows. It has
been calibrated on 4 non-overflowing events and then validated on 6 overflowing
events.
In a first step, a mesh convergence study was carried out in order to evaluate the error
related to the spatial discretization and to determine the mesh allowing to obtain results
"independent" of it. Three additional meshes obtained by dividing the number of finite
elements at each refinement by 4 were realized and used to simulate the event of 2003.
It appears that a mesh of intermediate size (approximately 27000 nodes) seems
required.
In a second step, propagation and quantification of uncertainties by an unidirectional
analysis method (creation of a set of 2000 members perturbed for each parameter and input
forcings and analysis of output water depths) was carried out on the numerical parameters
(wind influence coefficient, Strickler friction coefficients for 4 zones) and forcings of
the model (rivers discharges and maritime boundary conditions, meteorological
forcings).
The objective is to determine the variation coefficient (if possible standardized by the
input variation coefficient) of water depths for 13 major events between 1981 and 2016. The
exploitation of 1981 event results shows a predominance of the influence of the maritime
boundary conditions and the Strickler coefficient corresponding to the zone studied for the
estuarine part and the confluence, to which must be added the Garonne discharge as a
predominant parameter for the latter. Unsurprisingly, river zones are influenced primarily by
the coefficient of friction and the respective river flows of Garonne and Dordogne rivers. The
non-normalized variation coefficients were also calculated by taking into account the time
shift of the maritime input signal and, independently, the Arpege Ensemble Predictions
provided by METEO-FRANCE. The relative influence of the phase shift and the PEARP has
also been determined.
On the second hand, a variance sensitivity study (ANOVA) was carried out, by calculating
the total and partial Sobol indices, integrating the forcing variables time- and/or space
dependent. It has led to the identification of parameters and forcings to which the model is
most sensitive, as well as their inter-dependencies, in order to choose the variables to
assimilate.
Finally, it should be noted that this work has already made it possible to create a
database of multi-temporal simulations (over 13 time periods) on Gironde estuary that can,
after formatting, feed the SWOT simulator for Gironde Estuary, which is used to prepare the
Franco-American mission for the study of ocean and continental water depths . |
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