Morphodynamics of the Upper Pleistocene Garonne River (SW France):conditions of braiding/meandering transition

Frédéric Christophoul (1) , Vincent Regard (1) , Joseph Martinod (1) , José Darrozes (1)

1 GET - Géosciences Environnement Toulouse

The Garonne River developed through the Quaternary a huge network of asymmetric strath terraces. The last terrace is contemporary to the last glaciation. The mapping of the paleochannels preserved below the last Terrace of the Garonne River (southwest of France), by mean of remote sensing based on aerial photographs and field data, allows us to investigate the factors controlling factors of the transition braiding meandering related to the end of the last glaciation in the Pyrenees. Three channels patterns preserved in the infill of the lowest terrace of the Garonne River, could be evidenced. In chronological order, these patterns are: 1- braided channels before 30 ka, 2- low sinuosity gravel meandering channels until 15 ka and 3- high sinuosity gravel meandering channels before the end of the Younger Dryas. The available datings and palynologic data allow us to link this changes in fluvial morphology to the end of the last glaciation in the Pyrenees. The braided/meandering transition occurred 30 ka ago and the sinuosity sharply increased after 14 ka. This transition, in the context of the glaciar retreat in the upstream Garonne valley is the result of interplay between vegetation and hydrologic regime of the river, which evolved from a glacial regime with high water stage in spring/summer to a pluvio-nival regime with high water stage in winter/spring leaving uncovered gravel bars by the time of vegetation germination.

Mots clés: Fluvial dynamics; meandering; braiding; fluvial terrace; Garonne; France; würmian glaciation

Domaines: Géomorphologie

Frédéric Christophoul, Vincent Regard, Joseph Martinod, José Darrozes. Morphodynamics of the Upper Pleistocene Garonne River (SW France):conditions of braiding/meandering transition. 2014. ⟨hal-01005191⟩