Hydrodynamic modelling for early warning of sanitary risks in open swimming waters

International audienceSwimming in open water involves sanitary risks related to the presence of pathogenic microorganisms. To ensure the safety of bathers, a regulatory monitoring in the bathing area, based on faecal indicator bacteria (FIB), is required. Analysis of FIB concentrations can take more than 10 hours with in situ devices and more than 24 hours in the laboratory. Hence monitoring and forecasting of the sanitary conditions in urban bathing sites are essential for decision-making on their possible closure and its duration. In this paper, TELEMAC-3D hydrodynamic model was used to compute the time and space distribution of water temperature, velocity and contaminant tracers considering hydrometeorological conditions that can cause noticeable changes on the transfer time of the contaminant to the bathing area. The study site, La Villette, is an urban canal-basin system with a bathing area, located in Paris. The objectives focus on (i) how thermal stratification affects the transfer time of upstream contamination to the bathing area; (ii) the use of conductivity to track water quality changes after a storm event and (iii) the simulation of conductivity variation