The upper Rhine River is a highly harnessed and regulated river. EDF (a French electricity company) is in charge of eight dams on the upper Rhine River for producing hydro-electricity. In order to increase the safety and the competitiveness of the installations, but also to reduce their environmental impact, the sediment dynamics in these reservoirs has become a key factor to control and predict. In this study, we focused on the Marckolsheim reservoir, which is located 50 kilometers upstream the city of Strasbourg. Since its construction in 1961, this reservoir has been filled continuously with cohesive sediments, partially contaminated. Two field campaigns were performed in 2015 and 2016 under two different discharge conditions, with the objectives of quantifying the complex velocity fields on this site. The numerical codes TELEMAC-2D and SISYPHE were used to simulate in 2D the hydrodynamic and the suspended sediment transport of the reservoir. A ten kilometers long model was built and calibrated with the measured data of the 2015 and 2016 field campaigns, but also with measurements of sediment parameters that have been done separately. The originality of this model consists in an explicit 3D representation of the dam gates. An algorithm was implemented in TELEMAC in order to adapt the gates position at each time step, in conformity with the real regulation rules followed by the dam operator. By using upstream measured data of discharge and suspended sediment concentration, a four months period was simulated. The comparison of the simulated results with bathymetric surveys shows good agreements if specific properties of sediments related to settling processes are taken into account. Finally, the dynamics of the contaminated sediments was simulated. A 3D spatial distribution of the contaminated sediments in the reservoir was defined at the initial state by using in situ measurements. The fully coupled hydraulic-sediment-pollutant simulation performed over a single flood event gives first interesting highlights on the resuspension conditions of the contaminated sediments.
Achieving a sustainable management of sediment fluxes in existing or proposed reservoirs is a challenging but essential requirement for dam operators. Such objective is of utmost importance to avoid sedimentation-related consequences. Numerical modelling is of great interest to understand the flow and sediment dynamics in a reservoir, to simulate the long-term evolution of sediment deposits and to evaluate the efficiency of various management strategies. This paper presents recent case studies, which validate the feasibility and relevancy of such technical option. The progresses obtained on essential stages of the numerical modelling of sediments dynamics in reservoirs are particularly emphasized. Concerning the distribution of deposits, a promising field method based on an optimum combination of direct samplings with acoustic measurements and video auscultations is detailed. Feedbacks are then provided concerning an innovative device deployed in the field for a direct measurement of the settling velocity. Issues about the assessment of calibration parameters are also addressed in this communication. Lab experiments performed on deposits sampled in several reservoirs provide practical guidance to evaluate the erosion parameters of sediments. Finally, several examples of sediment dynamics modelling in reservoirs including both cohesive and non-cohesive sediment are presented.
COURLIS is a 1D sedimentology module coupled with MASCARET, 1D hydraulic code of the TELEMAC-MASCARET open source system. The code has been developed for more than 10 years, mainly for suspension sediment transport. Recently, the need of a 1D bedload code has been identified to model the long term evolution of rivers and reservoirs (several decades). New numerical schemes were implemented, some improvements were done in the geometry evolution algorithms. In terms of performance and robustness, the best scheme implemented is a finite volume upwind/downwind scheme. Several solutions are implemented to reduce calculation time. This new version of COURLIS for bedload transport was validated successfully on test-cases (Soni and Newton experiments). A real case has been simulated during an 11 year period. The calculation time is very similar to those obtained with codes tested in the benchmark and the results are in a good agreement with measurements and other code results. COURLIS (suspension and bedload transport) will be released in the next version of the TELEMAC-MASCARET open source system and so, it will be freely available for sedimentology community. Further developments are planned in 2018.
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