CS#8 - Sustainable river restoration, maintenance and management in Italy

The demonstration site, the Venice Lagoon Basin, is located in the Veneto region in northeast Italy. It concerns a rural/agricultural area (biogeographical type­: Continental).

© The hydrographic network at the border of Venice Lagoon. Blue: rivers flowing inside the lagoon; Red: “Acque Risorgive” Land Reclamation Consortium competence area.

Veneto Region ranks 2nd in Italy for soil consumption and in recent years is more and more suffering from river floods, drought and biodiversity loss. The maintenance of riverbanks is a fundamental practice for the proper functioning of the drainage network. The flow of water, especially in drainage areas where the water level is highly variable, erodes the banks and creates landslides within the channel. These landslides deposit the eroded material on the riverbed and thus reduce the water flow capacity of channels. During extreme rainfall events, this can lead to overflows and flooding of the surrounding areas. The maintenance of the banks is currently carried out by using hard infrastructures and unsustainable procedures. They require the quarrying, transport and installation of rocks and stones from the Alpine region, and result in a hardening of the canal bank. CBAR manages about 2300km of water streams in the Venice Lagoon’s drainage basin. During the period 2018-2022, CBAR required approximately 37.5 kTons/year of raw materials to execute the maintenance.

In the context of the demo site, canal bank landslides are a recurrent problem that requires maintenance in the near future. In these particular contexts, there is an opportunity to test and experiment a new more sustainable and nature-based approach of river bank maintenance. In addition to river management, the intervention is also particularly relevant for enhancing biodiversity and restoring natural habitats.

© Marco Cavallaro, Sebastiano Carrer                            © Vittore Negretto – made with QGIS

Climate projections suggest that the area could be subject to significant changes – mainly connected with temperatures’ increase - that could even motivate its inclusion in the Mediterranean biogeographical region. Thus, multiple types of impacts could affect the region. The available historical data for the Veneto region (1993-2022) suggest a notable and growing yearly variability of rainfall events, although changes in the total precipitation are not statistically relevant. Extreme precipitation (95° percentile) is expected to increase in a high emission scenario (RCP 8.5) from +60 to + 80% in coastal areas and from +80 to + 140% in alpine areas by 2100. This trend is expected to generate increasing erosion of riverbanks (due to more variable and more intense precipitation) and an increasing risk of flooding. Moreover, air temperature is increasing, following the general global warming. Historical regional data suggest a warming trend of 0.57° per decade (1993-2022) and all scenarios consistently show a further increase of temperature for this century. Finally, local biodiversity is threatened by several anthropic pressures (agriculture, urbanisation, pollution), with additional pressure exerted by climate change (changes in temperature and water availability).

Continuous River maintenance is the first prerequisite to avoid landslides along the banks, then it represents a fundamental type of measure to avoid flooding of territories. A proper and smooth water flow in the network may also mitigate the risk of water shortages for agriculture. In fact, the increase of temperatures affects not only the frequency of extreme storm and drought events, but also determines an increase in water demand of crops. Revegetation will contribute to decrease the risk of biodiversity loss and will increase the potential for ecological connection with other green areas.

In DS#8 two types of NBS will be implemented and monitored: (1) gentle maintenance, (2) slope reduction and vegetation.

NBS1: Gentle maintenance

The first NBS will be used to prevent erosion. It consists of maintaining a strip with uncut herbaceous vegetation at the base of the banks.

NBS2: Slope reduction and vegetation

The second NBS will be used in sections of the river where landslides are already present. A number of activities will be implemented:

• River restoration and maintenance. The core NBS will consist of the transition from a grey, "rigid", banks' management to a green management. The new approach will avoid the use of rocks and stones, favouring instead the widening of the canal bed and shaping fewer steep banks.
• Revegetation. Transplanting and revegetating the banks will also help soil consolidation and reduce the risk of landslides, while helping increase biodiversity.
• Capacity building. Workers will be trained in order to be able to adopt the proposed approach. This will result in development of new skills and formation of qualified workers.
• Social awareness. A dialogue with citizens and landowners will be initiated. In particular, farmers’ associations should be involved as important stakeholders.

Monitoring. This activity is fundamental to assess the advances of the NBS implementation process as well as the efficacy and the impact of the approach. Thus, all along the course of the project, appropriate indicators will be studied and then selected for monitoring.

Monitoring parameters will both refer to environmental and societal fields.

Environmental parameters will track changes in biodiversity, hydrology and geomorphology. Societal parameters incorporate capacity building and social acceptance Indicators.

Ambition during the project 

NBS will be in place probably at the end of the second year, so at the end of the project, experience will be gained about the land acquisition procedure. Moreover, the monitoring the evolution of the site for at least a couple of years will provide evidence-based on the measure effectiveness and workers will have gained a new know how. Moreover, the solution will have been discussed with several stakeholders, mainly farmers association, hence increasing the social acceptance of the NBS implemented.

Ambition after the project 

Implemented NBS will continue their function and the institution in charge of the maintenance will keep on carrying out the task, also to monitor the frequency needed for maintenance also in the medium-long term.