ContextThe European Water Framework Directive includes the risk assessment of floods (wetland and floodplain protections, management of sediment transport in the rivers…) in the sustainable management of water resources. In this context, models are extensively used to evaluate the effectiveness of various control strategies. Scientists and water resources planners extensively use hydrodynamic models to evaluate the effectiveness of various control strategies and of natural processes with regard to the requirements of the different EU policies (for instance on water, industrial pollution prevention, nature protection, agriculture). But, they are only approximate representations of complex natural systems and the evaluation of a model with respect to its ability to reproduce multiple criteria and behaviour of a real system is still problematic. For this reason, interactions between modellers and experimentalists are required to formulate more realistic assumptions on the behaviour of natural systems. In this perspective, we propose to work on an innovative approach, which leads to determine the efficiency of combining hydrological and geochemical datasets in order to provide new information – or a so-called “orthogonal view” – on river system behaviour.ObjectivesThe overall goal of this project is to provide hydrodynamic models for the risk management of floodplain contaminations by some trace metals, recognized as Potential Harmful Elements (PHE). We propose to develop a numerical tool to compute the spatial dispersion of the PHE contamination in riverbeds and floodplains. The innovative part of this project comes (1) from multi-objective hydraulic model calibration that makes use of a large variety of complementary data sets and (2) from new developments in the field of in situ hydrological monitoring and geochemical tracers.Four specific tasks are defined, requiring a multidisciplinary approach that will integrate these scientific developments: (1) the calibration of hydraulic models will be based on an innovative combination of hydrochemical approaches in order to provide new information (“orthogonal view”) on river system behavior; (2) the quantification and the characterization of river sediments will be investigated by combining turbidometry, and other physico-chemical variables for suspended sediments and in taking into account the turbulence due to floodplain vegetation during flooding; (3) the origin of PHE transported during flood events will be studied by coupling current and new powerful geochemical tracers with a spectral fingerprinting approach (NIRS); (4) the last task consists in using hydrological regime change scenarios to assess their impact on the input and the deposition of contaminated sediment particles in the floodplains.Study areaDue to poor river water quality that has various origins, the Alzette River floodplains suffer from substantial PHE contamination. A recent study of the EVA department of the CRP-Gabriel Lippmann determined the spatial dispersion and the origin of the contamination in the alluvial soils of the Alzette River.