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Anthropogenic activities since the end of the Little Ice Age: a critical factor driving fluvial changes on the Isonzo River (Italy, Slovenia)

Activités anthropiques depuis la fin du petit âge glaciaire : un facteur critique contrôlant la métamorphose fluviale de l’Isonzo (Italie, Slovénie)
Isabelle Siché and Gilles Arnaud‑Fassetta
p. 183-199

Abstracts

The Isonzo is a 140‑km long river that draws its source in the Julian Alps in Slovenia and joins the Gulf of Trieste in the Northern Adriatic, Italy. Its catchment area (~3400 km2) consists of mid‑altitude mountains (70%), a piedmont (22%), and a coastal plain (8%) influenced by Mediterranean climatic conditions. The river is a high‑energy system due to its pronounced hydraulical gradients and with frequent damage to man‑made structures. The objective of this study is to determine the recent functioning of the Isonzo River by (i) a diachronic (from the Little Ice Age), plan‑form analysis of the alluvial plain, using old maps, topographic maps of the IGM and aerial photographs, and (ii) an analysis of channel incision and sediment transport, using data derived from national and regional water services and field observations. Over the last 200 years, the Isonzo River shows a clear tendency to active‑channel narrowing between 15 km and 2 km upstream of the river‑mouth. This phenomenon was accompanied by an incision of the active channel, estimated to be between 0.5 m and 1.5 m at the most vulnerable sites. In the context of climate change since ca. 1860, the narrowing/incision of the active channel increased from the 1880s to 1920s, and prticularly since 1960, because of human impacts (channelisation, embankments, dams) in the catchment, and despite the increase of flood frequencies. The recent hydro‑morpho‑sedimentary functioning of the Isonzo shows that the river is still in a transitional phase towards a physical equilibrium that changes after every human intervention in the active channel.

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Excerpt

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Outline

1 ‑ Study area
1.1 ‑ Morpho‑structural units, hydrography, and alluvium discontinuum
1.2 ‑ Climate and hydrological functioning
1.3 ‑ Land use and recent river management
1.3.1 ‑ General considerations at the catchment scale
1.3.2 ‑ Water projects
2 ‑ Methods
2.1 ‑ Selected area
2.2 ‑ Iconographic data
2.3 ‑ Hydro‑morphometric variables
3 ‑ Results
3.1 ‑ Active‑channel narrowing: A continuous phenomenon
3.2 ‑ Reduction of the braiding index
3.3 ‑ Substitution vs. maintenance of the sinuous channel pattern
3.4 ‑ Active‑channel incision
4 ‑Discussion: Causes of the ‘fluvial changes’
4.1 ‑Continuous decrease in sediment supply
4.2 ‑ General and local disturbances of river discharge
5 ‑ Conclusions

First lines

The Isonzo River (Soča in Slovenia), a cross‑border river straddling the Italo‑Slovenian border, constituted a combat front during the two world wars (fig. 1A).

Fig. 1 – Physiography, hydrography and geology of the study area

Fig. 1 – Physiography, hydrography and geology of the study area

(A) The Isonzo catchment. (B) Geological section across the mountains, the piedmont and the coastal plain in the Isonzo catchment (after Merlini et al., 2001). 1: Quaternary formations; 2: Canavella Formation; 3: Flysch of “Grivo”; 4: Flysch of Cormons; 5: Cretaceous limestone; 6: Jurassic limestone; 7: Dolomites; 8: Montebello Formation.

The river is 140‑km in length and drains a small catchment (~3400 km2) located in the Julian Alps. Downstream of the mountainous area, the Isonzo River flows through the piedmont and coastal plain, including the region of Friuli‑Venezia Giulia, and the wave‑dominated delta (COVELLI et al., 2004) prograding in the Gulf of Trieste, in the north of the Adriatic Sea. The main interest of the Isonzo River is t...

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References

Electronic reference

Isabelle Siché and Gilles Arnaud‑Fassetta, « Anthropogenic activities since the end of the Little Ice Age: a critical factor driving fluvial changes on the Isonzo River (Italy, Slovenia) », Méditerranée [Online], 122 | 2014, Online since 19 June 2016, connection on 26 March 2017. URL : http://mediterranee.revues.org/7253 ; DOI : 10.4000/mediterranee.7253

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About the authors

Isabelle Siché

University of Paris‑Diderot (Paris 7), CNRS (UMR 8586 PRODIG), Paris, France

Gilles Arnaud‑Fassetta

University of Paris‑Diderot (Paris 7), CNRS (UMR 8586 PRODIG), Paris, France, gilles.arnaud‑fassetta@univ‑paris‑diderot.fr

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