Depuis 200 ans, l’Isonzo montre une nette tendance à la contraction de sa bande active sur le tronçon situé entre 15 km et 2 km en amont de l’embouchure. Cette étude a pour objectif de déterminer le fonctionnement actuel de l’Isonzo par 1) une approche diachronique de l’état de surface dans la plaine alluviale depuis le PAG, utilisant pour cela des cartes anciennes, des cartes topographiques de l’IGM et des photographies aériennes, et 2) l’analyse de l’incision du chenal couplée au transport sédimentaire, grâce aux données des services hydrauliques nationaux et régionaux et des observations de terrain. Le fleuve dispose d’une forte énergie en raison de gradients hydrauliques élevés, à l’origine de dommages causés chaque année aux ouvrages d’art et aux structures hydrauliques. Son bassin‑versant (~ 3 400 km 2) est constitué de moyennes montagnes (70 %), d’un piedmont (22 %) et d’une plaine côtière (8 %) sous conditions climatiques méditerranéennes. L’Isonzo est un fleuve long de 140 km qui prend sa source dans les Alpes Juliennes en Slovénie et se jette dans le golfe de Trieste en Italie, au Nord de l’Adriatique. 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. 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. 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. 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. 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. The river is a high‑energy system due to its pronounced hydraulical gradients and with frequent damage to man‑made structures. Its catchment area (~3400 km 2) consists of mid‑altitude mountains (70%), a piedmont (22%), and a coastal plain (8%) influenced by Mediterranean climatic conditions. 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.
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