When releasing a pollutant into a river, it is important to know the downstream distance from which the pollutant will be homogeneously distributed throughout the cross-section, in order to be able to delimit the mixing zone. To estimate this, the usual method is to apply an advection-diffusion model based on the estimation of a transverse mixing coefficient. While numerous formulas exist for estimating this coefficient, most of them have only been validated in certain river configurations.
In a previous study, Lorris Gond  divided a part of the Durance into successive reaches, according to the hydromorphological facies encountered, and determined the transverse mixing coefficient in each section by releasing dye. These results confirm the hypothesis of a transverse mixing process specific to the riffle-pool sequences encountered in the Middle Durance. The aim of the proposed thesis is to verify this hypothesis in rivers with riffle-pool type structures. The aim is then to determine a methodology for computing a global mixing coefficient for the structure based on a priori knowledge of the facies, so as to avoid the need for new in situ measurements each time the bed undergoes morphogenic changes. To this end, the thesis will involve field characterization of the geometry of a section of the middle Durance, dye release to quantify the transverse mixing coefficient in the river, and laboratory experiments on a small-scale riffle-pool structure.
A master internship is proposed by the team in addition to the thesis.