The Adige River, having a total length of of 410 km, is the longest river in South Tyrol and the second longest in Italy, and it is located in the North-Eastern part of the country. The Adige springs near the Resia Pass, close to the borders with Switzerland and Austria, it flows through the Resia reservoir and then run on the bottom of the U-shaped Venosta valley. It laps Merano and and Bolzano as well. After the confluence with the Isarco River at Bolzano, the Adige flows South through the Trentino-Alto Adige region (Lagarina Valley). It enters in the Po lowland near Verona and ,flowing South-East, after several long meanders the Adige flows into the Adriatic Sea just South of the town of Chioggia and North of the Po River delta. It drains a basin of 12,200 km2.
Overview of the study area in the Authonomus Province of Bolzano. The part of river Adige catchment involved is indicated in green and it closes at Ponte Adige near the city of Bolzano.
The restored sites included in this case study are located along the Adige River in South Tyrol region. The drainage area is 2,700 km2, with glaciers occupying the 2.88% of the total surface. The hydrological regime of the river is nivo-glacio-pluvial and the geological composition of the Adige catchment is mainly represented by slate, paragneiss and porphyry.
The Adige River between Merano and Bolzano has been strongly channelized during the last centuries. The natural morphology of the upper part of this reach formerly included multi-channels, bars, islands and confluences with the tributaries, while the lower part, upstream the confluence with the Isarco River, was mainly a single channel river characterized by a sinuous pattern with alternated bars. After the artificial modification of river morphology, carried out at the beginning of the XIX century, the Adige is now confined within a narrow channel and flows downstream along a straight line. The average river width is between 40 and 60 m, the water depth is generally constant and insular areas are quite rare or restricted and the riverbed lacks a solid structure and a diversified habitat. The vegetation varies according to the river section and it is mainly composed by willow (Salix), black poplar (Populus nigra) and black alder (Alnus glutinosa). Allochtonous species are also present: black locust (Robinia pseudoacacia) and tree of heaven (Ailanthus altissima). The fish species present at the confluence between the Adige and Isarco River are river trout (Salmo trutta fario and Salmo trutta marmoratus), grayling (Thymallus thymallus), common barbel (Barbus barbus), European bullhead (Cottus gobio), Italian Chub (Squalius squalius) lamprey (Lampetra fluviatilis) and European carp (Cyprinus carpio). Many restoration interventions have been carried out along the Adige reach between Postal (South of Merano) and Bolzano. In particular, two main segments have been investigated within HyMoCARES project:
1) between km 79 to km 81 (respect to the watercourse spring), in Postal;
2) between km 97 to km 99 with, in Ponte Adige.
Overview of the restored sites (in red) along the Adige River
The restoration project
The Civil Protection Agency of the Autonomous Province of Bolzano has been carrying restoration works along the Adige River since 2002 with the aim of improving the physical heterogeneity, diversifying the natural habitats and thus enhance the value of the aquatic communities. In particular, river restoration works started in 2008 at Postal and in 2013 at Ponte Adige.
The restoration actions included:
- Channel widening and riverbanks renaturalization. In some river stretches riverbanks have been smoothed to recreate “natural” bank shape;
- Recreation of river morphological features such as flow deflectors, island or inlets establishing spawning gravel zones for fish reproduction;
- Distribution of boulders in the river bed to create morphological structures and to slow down water flow;
- Promotion of theconnection between the Adige River and the close cycle path, running from Bolzano to Merano, through the realization of smoother embankments that cyclists can easily access;
- Improving the lateral connectivity between the Adige River and its tributaries.
Restoration works in right bank of the Adige River (2012) with creation of inlets along the reach, boulders distribution on the riverbed and connection of the lateral ditches favoring fish migration and fish habitat restoration