The primary objective of this thesis is to address the following questions: How can biogeochemical data be used to trace the origin of water at the outlet of a watershed based on the sources contributing to the flow in a river? And how can biogeochemical data be used to evaluate the results of a distributed hydrological model?
A specific methodology was developed for the peri-urban Ratier watershed, using the distributed hydrological model J2000P.

Distributed hydrological models are promising tools for the identification of flow contributions in peri-urban catchments, but face difficulties in the validation of the results. Biogeochemical mixing models appear to be effective for validating the results of a distributed hydrological model based on field data. By identifying the sources and their biogeochemical signatures, it is possible to separate the flow by applying a mixing model. This method is applied to the Ratier catchment, a sub-catchment of the Yzeron and a study site for the Observatoire de Terrain en Hydrologie Urbaine (OTHU) and the national research infrastructure Observatoire de la Zone Critique : Applications et Recherche (OZCAR), in order to evaluate the results of the J2000P distributed hydrological model. Nine sources were identified and sampled, corresponding to different land uses (e.g. forest, grassland), hydrological compartments (e.g. aquifer) and urban point discharges (e.g. sewage system). Six contrasted hydrological events were sampled at two points in the catchment. A wide range of biogeochemical indicators were analysed including : major chemical compounds, dissolved metals, stable water isotopes, microbial indicators and dissolved organic matter characteristics. A flow spatial decomposition component was developed in the J2000P model to identify the simulated contributions and allow for a comparison with the decomposition results from the mixing model. Results show distinct biogeochemical signatures between sources thanks to the use of conventional tracers with original tracers. Evaluation of the J2000P model revealed significant differences between the contributions simulated by the model and those estimated from the mixing model. Based on those results, suggestions are made for improving the J2000P model.

Funding

50% INRAE AQUA department, 50% EUR H2O’Lyon.

For more information

• Olivier Grandjouan. Apports de la biogéochimie pour l’évaluation d’un modèle hydrologique distribué en milieu péri-urbain. Université Claude Bernard Lyon 1 [2024], 2024. Français. https://theses.fr/s262769
• Grandjouan, O., Branger, F., Masson, M., Cournoyer, B., & Coquery, M. (2023). Identification and estimation of hydrological contributions in a mixed land-use catchment based on a simple biogeochemical and hydro-meteorological dataset. Hydrological Processes, 37(12), e15035. https://doi.org/10.1002/hyp.15035
• Grandjouan, O., Branger, F., Masson, M., Cournoyer, B., Robinet, N., Dusseux, P., Dominguez Lage, A., Coquery, M., Hydrograph separation using biogeochemical signatures and a mixing model in a peri-urban catchment, HESS, submitted.

Cite the thesis

Olivier Grandjouan. Apports de la biogéochimie pour l’évaluation d’un modèle hydrologique distribué en milieu péri-urbain. Autre. Université Claude Bernard - Lyon I, 2024. Français. ⟨NNT : 2024LYO10045⟩. ⟨tel-04951001⟩

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