When pollutants are released into a river, it is important to understand the downstream distance at which the pollutant will be evenly distributed across the entire cross-section, in order to define the mixing zone. The usual method to estimate this distance involves applying an advection-diffusion model based on the estimation of a transverse mixing coefficient. Although many formulas exist to estimate this, most are validated only in specific river configurations.

In a previous study, Lorris Gond [2022] divided a section of the Durance River into successive segments based on the encountered hydromorphological facies and determined the transverse mixing coefficient in each segment using dye tracing. These results confirm the hypothesis of a transverse mixing process specific to the riffle-pool structures found in the middle Durance River.

The objective of the proposed thesis is to verify this hypothesis in rivers that feature riffle-pool structures. The goal is then to develop a methodology for calculating a global mixing coefficient for the structure based on prior knowledge of the facies, in order to avoid the need for new in-situ measurements each time there is a morphogenic change in the riverbed. This thesis will include field characterization of the geometry of a section of the middle Durance River, dye tracing experiments to quantify the transverse mixing coefficient in the river, and experimental reproduction in a laboratory channel of a riffle-pool structure.

Funding

CEA, MRISQ project

References :

Lorris Gond. Etude du mélange transverse en écoulement à surface libre non uniforme. Mécanique des fluides [physics.class-ph]. Université de Lyon, 2022. Français. http://www.theses.fr/2022LYSEI027