Ecohydrological integrative approach to restoration interventions on Pellice River (Piedmont Region, Italy)

Interventions of risk mitigation from floods can no longer be separated from the evaluation and improvement of river ecological status. Specific reference is made to the European framework on water quality 2000/60/CE which in turn, in Italy, has been applied in the so-called Management Plan of the Po basin (2015-2021).

The Pellice River is the recipient of the first multi-objective interventions in Italy that respond to this innovative vision of water courses. It is therefore a pilot case that distinguishes from previous design approaches. The areas of intervention have been identified at institutional level (AIPO, Regional and River Basin Authority), selecting the zones where sediment management and flood defense interventions also include habitat improvement. The working group had the task to prepare the detailed design in order to respond to the need to recreate natural conditions of the river environment and hydraulic risk mitigation.

For this purpose, the Pellice River has been studied for a length of about 20 km from the geological, hydrological, hydrogeological, geomorphological and ecological point of view, thanks to the collaboration of a multidisciplinary group, composed by engineers, biologists, ecologists, foresters, ichthyologist and river vegetation specialists. An analysis of the aquifer levels and a monitoring of the aquatic habitat were also carried out, i.e., through the identification of trout spawning. In this first phase, the aim of the study was to reach adequate information to photograph the morphological, ecological and vegetational status of the watercourse in the intervention areas.

In a second phase, the analysis has been completed by means of mono and two-dimensional hydraulic modeling not only of the flood events but also with a 1- year return time event. This is necessary to evaluate the reactivation of designed secondary channels, the effectiveness of sediment management interventions and the realization of flow diversion structures made with natural elements that can also act as a refuge for animals. These results together with the maximum and minimum depth of the aquifer made it possible to design improved aquatic animal and vegetation habitats.

Finally, some geomorphological indicators have been coupled with vegetational and ecological ones in order to propose a practical instrument for the evaluation of interventions effectiveness over time.