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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

Changements hydrobiomorphologiques et facteurs de contrôle d’un fond de vallée alpine depuis la deuxième partie du xixe siècle. Étude de cas du Haut-Guil, bassin de la Durance, Alpes françaises du Sud
Gilles Arnaud-Fassetta and Monique Fort
p. 159-182


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.

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1 - Hydromorphological changes on the floodplains during the last few centuries: State of the art
2 - Study area
2.1 - Geomorphological context
2.2 - Morpho-sedimentary characteristics
of the Guil River
2.3 - A long history of floods
2.4 - Human activities
3 - Methods
3.1 ‑ Hydrographic network characteristics
3.2 - Bed-material grain size and channel hydraulics
3.3 - Channel planform changes
3.4 - Dendrochronology
3.5 - Anthropogenic impacts
4 - Results: Active-channel planform changes between 1855 and 2013
4.1 - General trend
4.2 - From 1855 to 1956
4.3 - From 1957 to 2013
5 - Discussion: What part of active‑channel changes is devoted to hydroclimatic variability and/or human factors?
5.1 - General considerations
5.2 - Human activities: a secondary factor
5.3 - Hydro-climatic variability: a critical impact
6 - Conclusions

First lines

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...

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Electronic reference

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 25 March 2017. URL : ; DOI : 10.4000/mediterranee.7245

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About the authors

Gilles Arnaud-Fassetta

University of Paris-Diderot (Paris 7), CNRS-UMR 8686 (PRODIG),

By this author

Monique Fort

University of Paris-Diderot (Paris 7), CNRS-UMR 8686 (PRODIG),

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