Thermohydraulics modeling of the Garonne River, France in relation to freshwater fishes : statistical and deterministic approaches

• Main Author: Larnier, Kévin
• Other Authors: Institut de mécanique des fluides de Toulouse (IMFT), Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Centre National de la Recherche Scientifique (CNRS)-Institut National Polytechnique (Toulouse) (Toulouse INP), Université de Toulouse (UT), Institut National Polytechnique de Toulouse - INPT, Denis Dartus
• Format: Doctoral or Postdoctoral Thesis
• Language: French
• Published: HAL CCSD 2010
• Subjects: Models; Statistic; Deterministic; Stream temperature; Shallow water; Diadromous fishes; Modélisation; Statistique; Déterministe; Température de l’eau; St-Venant; Amphihalins; [SDU.STU]Sciences of the Universe [physics]/Earth Sciences; Atlantic salmon
• Online Access: https://theses.hal.science/tel-04274824; https://theses.hal.science/tel-04274824/document; https://theses.hal.science/tel-04274824/file/larnier.pdf

Fish species with strong thermal requirements (i.e. Atlantic salmon) are very sensitive to temperature evolution and particularly to large increases. An investigation conducted on the Garonne River (France) during the last three decades revealed global water warming along with an increase of the high temperature period duration. Large impact of this evolution on the survival and breeding of migrating fish species was also reported. Study was thus conducted on a specific reach of the Garonne River located between the immediate upstream of Toulouse and the upstream of the Malause dam. The issue of water temperature warming is particularly relevant on this reach, with an average increase of 2°C between upstream and downstream and temperatures above 25°C frequently reported. Potential causes are numerous: drastic low-flow regime (quoting SDAGE Adour-Garonne), impacts of surface fluxes that are important due to bed shape (wide and shallow), anthropogenic impacts, etc. Large amount of climatic and hydraulic data are used to make a clear determination of the processes involved in the thermal regime evolution of this reach. Trend and correlation analyses and use of statistical models indicate the strong relation between stream temperature and climate. Low flows also seem to be related to water temperatures during summer periods. Statistic and deterministic models give good results in estimating high daily mean water temperatures (RMSE ranging from 0.99°C to 1.22°C) and predicting water temperatures threshold crossings related to the migrating conditions of Atlantic salmon.Finally, a one-dimensional numerical model that solves both shallow water and thermal equations is developed. Both the formulation of the St-Venant equations (high variability in slope, gates …) and the phenomena taken into account in the water temperature model (lateral influx, surface fluxes, bed conduction …) allows studying the evolution of fluxes driving water temperature evolution. Future evolution of the water temperature at the 2050 horizon is ...