CERFACS CERFACS Scientific Activity Report Jan. 2010 – Dec. 2011

DATA ASSIMILATION FOR HYDRAULICS AND HYDROLOGY
4.3 Investigation for the use of data assimilation techniques to
improve the modeling of the hydrodynamics of the Berre
lagoon with TELEMAC 3D (S. Ricci, A. Piacentini, O. Thual, in
collaboration with LNHE)
The Berre lagoon, located in the South East of France, is one of the largest lagoons in the Mediterranenan
area. It is located in the South East of France. It is a receptacle of 1000Mm 3 where salty sea water
meets fresh water discharged by the hydroelectric plant at Saint-Chamas and by natural tributaries (Arc
and Touloubre rivers). EDF fresh water discharge can reach up to 1200 Mm 3 per year and has a strong
seasonal variability. To better qualify and quantify the relationships between the salinity of the lagoon, the
fresh water inputs (from the powerplant and from the rivers), the water exchanges with the sea and the wind
mixing, EDF started an in-situ continuous monitoring of the lagoon and built a 3D hydrodynamic model
with the TELEMAC software. EDF R&D at LNHE aims at maximizing the benefits of this numerical tool
by simulating new scenarios of exploitation and optimizing the operation of the hydroelectric production
while preserving the lagoon ecosystem.
The objectif of the project at CERFACS is to investigate the use of data assimilation techniques in the
context of the Berre lagoon study, especially to improve the representation of the salinity field using CTD
salinity profiles. The developement of the 3D-FGAT algorithm is on-going at CERFACS : it consists in
correcting the salinity state at the beginning of an assimilation window. This approach is the same as the
one used in meteorology, oceanography and atmospheric chemistry. The successul achievement of this
project partly relies on the good use of the expertise at CERFACS in other applicative fields [DA7],[7],
[9],[8], available at CERFACS, for variational data assimilation and optimization.
The implementation of the algorithm for the prototype is currently being done using the Open-PALM
software. Some of the technical aspects for this part have already been solved in close collaboration with
the Open-PALM team at CERFACS. This choice was made to ease the development and the use of the
assimilation prototype. Still, this collaborative project should fit into EDF R&D dynamics regarding the use
of the SALOME platform. The project benefits from CERFACS’s expertise with this coupling software, as
well as from LNHE involvement with the use of this tool (1D/2D hydraulic coupling, data assimilation for
1D hydraulic).
4.4 Investigate the use of satellite measurements in conjunction with
in situ data to improve water ressources studies in the framework
of data assimilation in large scale hydrology (M. Mouffe, S. Ricci,
in collaboration with LEGOS/CNES, CNRM)
About 73% of global water ressources is provided by continental waters. Understanding and forecasting
these ressources is then a crucial issue that can only partly be addressed with in situ observations.
Hydrodynamics modeling plays a major role in this study but as data are required to initialize and force
these models, modeling can also partly adress this question and major uncertainties remain on estimation
of water levels and discharges. Observation from space, especially altimetry can notably help reducing
uncertainties. The joint mission SWOT (CNES and NASA) to be launched in 2020, will provide wide
swath (120 km) altimetry data with a global coverage over oceanic and continental waters. These data will
enable the observation of middle size rivers (from 50 m wide) with a temporal frequency of at most 22 days.
In the framework of a post-doc funded by CNES (Mélodie mouffe, started in September 2011), at
CERFACS, a study on the use of SWOT data for large scale hydrology was initiated. The HYMAP
hydrological model was developped at CNRM in the framework of a CNES post-doc. This model is forced
88 Jan. 2010 – Dec. 2011