International audienceThe purpose of this study is to propose a methodological essay for defining evolutionary trajectories of channel planforms and to examine the channel change in the middle Garonne River (southwest France) over a 130-year period. The study focuses on a reach of ~90 km situated downstream from the city of Toulouse. A set of four historical maps (1868, 1940s, 1970s, and 2000s) is used to build a geomorphometric diachronic database. Data processing through mixed multiple factor analysis (MFAmix) and hierarchical cluster analysis (HCA) allows distinction between four homogeneous zones within the study reach, depending on their evolutionary trajectories. Channel behavior in the upstream and median zones evolved as of the beginning of the study period (narrowing of the fluvial area, colonization by vegetation, and removal of alluvial bars), likely owing to punctual anthropogenic actions. The downstream zone is characterized by stabilization of the channel and alluvial bar removal over the second half of the twentieth century, coinciding with the campaign undertaken by French local authorities between 1960 and 1984 to protect river banks. The role of ACCEPTED MANUSCRIPT climate transition between the Little Ice Age (LIA) and the onset of the Global Warming period (GW) is also discussed. Results generally are consistent with the chronology established for most European rivers
Article history: Available online xxx a b s t r a c t This paper discusses the evolution of the Tech river lower plain, (western Mediterranean) from the Late Middle Ages, using geomorphological, archaeological and historical data. Geoarchaeological data was obtained from coring and trenching near a buried village and chapel. Radiocarbon and archaeological dating are used to reconstitute sedimentation rates and major flood event chronology. Additional data about channel avulsion are provided by historical data. Increases in sedimentation rate, flooding plain enlargement and repeated avulsion are identified between the last 13th to 15th century AD. This attests to a shift from low water-level regime (LWR) to flood dominated regime (FDR). Climatic or anthropogenic causes of this change are discussed on the basis of regional synthesis. On the western Mediterranean scale, 1250/1350 AD seems to be a wetter phase, associated with the progressive onset of the Early Little Ice Age phase from 1330 to 1450 AD.
Géohistoire des risques et des patrimoines naturels fluviaux Construction géohistorique du « sauvage » de la Garonne toulousaine : quelle part de naturalité dans les paysages fluviaux ? (1 ère partie) Geohistorical construction of the "wild" of the middle valley of the Garonne (near of Toulouse
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