Sustainable River Restoration and Maintenance in the Venice Basin: Slope reduction and vegetation

Such a transition is being pursued through the adoption of Nature Based Solutions, both during the ordinary maintenance and in case of extraordinary restoration after bank landslides.

CBAR’s vision includes using nature as a solution for the extraordinary maintenance. The traditional approach for restoring landslides consists in placing rocks and stones (coming from quarries located in the mountain areas) to consolidate the banks. The NBS approach, called Slope reduction and vegetation, involves widening the riverbed, shaping a bank profile with a gentler slope, and subsequently planting native shrubs. This approach increases the stability of the banks (thanks to the roots’ ability to consolidate the soil), has positive effects on water quality (given plants capacity to act as a buffer abating pollution from farmland) and brings additional benefits such as counteracting biodiversity loss, stopping soil consumption, involving lower carbon emission and higher carbon sequestration, and landscape improvement.

Restoration of bank landslides with “Slope reduction and vegetation“ (right image) compared to traditional approach using rocks (central image)

The adoption of a nature based approach is accompanied by stakeholder engagement and social awareness campaigns with the final aim of increasing the social acceptance and at the same time creating a “culture” for nature based solutions. Farmers, administrations, citizens and NGOs are involved in the process. The possibility to have access to territorial data to better understand the territory and the request to promote a new culture is a request that emerged as a co-creation process. This was operationalized through several engagement activities, including “citizen science” events and the co-development of a collaborative platform/tool for sharing, visualising and updating environmental and territorial data, facilitating cross-sector use, monitoring and interoperability. The activities conducted during the Transformation Labs in the Veneto Region are detailed in the dedicated report.

A “Slope Reduction and vegetation” NBS will be implemented along two stretches of the Pianton watercourse, located in the neighbourhood of the municipality of Mogliano Veneto. To assess the performance of this intervention, two stretches of the same watercourse will be used as references. Two other watercourses, Vernise and Scandolara, in the municipality of Zero Branco, where similar interventions were conducted several years ago, will serve as references for a mature stage of the NBS. The other three sites will be utilized as reference cases representing the traditional approach.

Several indicators are utilized to assess the NBS's performance in terms of environmental, social, and economic benefits. The assessment combines biodiversity monitoring and hydraulic modelling. The modelling activity is supported by a system of water level sensors and by the execution of topographic and geognostic surveys (to establish the stratigraphy, the grain-size profile, and the geotechnical characteristics of the terrain). The velocity/flow rate was determined through specific campaigns with the use of a StreamPro Acoustic Doppler Current Profiler.

The aim of the hydraulic modelling activities will be to demonstrate that the modifications induced by the adoption of the NBS will not affect the efficiency of the drainage network, will not produce any increase in the flood risk and will not affect the stability of the banks, i.e. the risk of erosion with occurrence of landslides.

The environmental performance of the NBS is assessed through indicators related to biodiversity. In particular, monitoring includes the changes in birds, odonates, and lepidoptera populations as well as plant communities associated with the widening of the riverbed and the re-naturalization of the banks. Monitoring was already executed for all biological compartments before the implementation of the NBS (year 2024). Similar monitoring will be carried out for two years (2026 and 2027) after the implementation of the NBS. In addition, a specific analysis of the changes in the presence of the invasive species Myocastor coypus (so-called nutria or coypu) along the watercourse will be performed. A survey of nutria burrows distribution in the Pianton River before the implementation of the NBS was conducted; a second survey will be carried out in 2027.

From a social perspective, we expect to improve social acceptance, increase the sense of place and community connection, and enhance environmental awareness and social learning about ecosystem functioning. From an economic perspective, an in-depth cost-benefit analysis will be conducted following a detailed analysis of the causal interactions between all processes involved in the proposed approach (compared with the traditional one). See the section “Making the Economic Case for River Restoration”.

The performance of the implemented solution will also be assessed under different climatic scenarios.

The elaboration of a cost-benefit analysis is crucial for mainstreaming NBS in the region. Direct benefits in terms of flood risks (through riverbank restoration) are accompanied by co-benefits such as combating biodiversity loss, reducing material, soil consumption, and greenhouse gas emissions, while increasing carbon storage. Potential social and economic dis-benefits, such as the perception of lack of maintenance and economic losses due to the reduction of available areas for agricultural production, will be evaluated and compared with other benefits such as environmental awareness and social capacity building.

You can explore the detailed cost-benefit analysis in the full report for Italy [Link]

The cost-benefit analysis will determine the overall sustainability of the NBS transformational approach and will inform future activity - at least - in the area of competence of the land reclamation consortium Acque Risorgive. The potential for replication will be assessed, identifying feasible areas and costs. The implementation of the NBS on a large scale could provide additional co-benefits such as the formation of ecological corridors able to strengthen the Regional Ecological Network.

Veneto Region Ecological Network (green), NBS implementation sites Pianton, Vernise, and Scandolara (dark green), and the network of watercourses where additional ecological corridors may be identified. For the sake of clarity, the image portrays only a portion of the network focusing on the neighbourhood of the NBS implementation sites, but the analysis will be conducted for the entire area of competence of CBAR.

Veneto Region Ecological Network (green), NBS implementation sites Pianton, Vernise, and Scandolara (dark green), and the network of watercourses where additional ecological corridors may be identified. For the sake of clarity, the image portrays only a portion of the network focusing on the neighbourhood of the NBS implementation sites, but the analysis will be conducted for the entire area of competence of CBAR.

There are several ways to verify whether a transformational approach to water management could be adopted in your municipality. Check the approach currently adopted by the land reclamation consortium in your area, and review the Piano Comunale delle Acque (Municipality Water Management Plan) valid for your municipality. You may not know that, very recently, thanks to close collaboration with the NATALIE consortium partners, the Province of Treviso launched a call for funding sustainable maintenance of ditches in provincial municipalities.

You can use the NATALIE tools to perform a preliminary assessment of the suitability of this solution for your specific case scenario.