In the last 200 years, floodplains have experienced more or less significant hydromorphological changes of anthropogenic origin. However, this mode of evolution cannot be extrapolated to all catchments because some floodplains have maintained a relatively ‘natural’, hydro-climatic controlled functioning, therefore their evolution should be nuanced. There is not a single ‘model’ of floodplain evolution but a variety of different ones, according to the physical characteristics of the catchment and anthropogenic pressures on the environment. Unlike the Alpine and pre‑Alpine valleys at lower altitude, high mountain catchments may have followed a mode of evolution much less constrained by human actions, because of their direct connection with debris sources and the energy of hydro-climatic events. In order to test this hypothesis, we selected one of the major tributaries of the Upper Durance River, the Guil River, which offers the opportunity to assess the respective impact of climate (a...
Hydro-bio-morphological changes and control factors of an upper Alpine valley bottom since the mid-19th century. Case study of the Guil River, Durance catchment, southern French Alps
Much research carried out along rivers at intermediate altitudes has concluded that the general trend of decreasing bedload supply is primarily a result of human action, and only secondarily a response to changes in climate and vegetation. In contrast, we have recently shown that, in the upper reaches of Alpine valleys, the shaping of active channels has been mostly dependent upon hydroclimatic variability, at least during the last fifty years. We propose to apply this hypothesis within a broader temporal framework so as to include the Little Ice Age period. The analysis is based on several types of data: longitudinal and cross profiles, old topographical maps, and aerial photographs. We took account of active channel width and area, sinuosity and incision indices, and engineering structures. We used dendrochronology to improve constraints upon the age of terraces and to help assess the impact of high magnitude floods on riparian forest development. We assert that, whereas the general trend is dominated by channel incision, the overall instability of the active channel is mainly controlled by the passage of low-frequency high-magnitude hydroclimatic events (1957, 2000). Although flood-control structures are generally efficient, the last 50-years of land-use changes have reduced the channel capacity of the Guil, increasing the vulnerability of human installations to damage.
Mots-clés :petit âge glaciaire, vallée alpine, métamorphose fluviale, crue exceptionnelle, ripisylve, gestion fluviale
Keywords :Alpine valley; channel change; rare flood; riparian forest; river management; Little Ice Age
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of the Guil River
Gilles Arnaud-Fassetta and Monique Fort, « Hydro-bio-morphological changes and control factors of an upper Alpine valley bottom since the mid-19th century. Case study of the Guil River, Durance catchment, southern French Alps », Méditerranée [Online], 122 | 2014, Online since 19 June 2016, connection on 26 April 2017. URL : http://mediterranee.revues.org/7245 ; DOI : 10.4000/mediterranee.7245Top of page
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