Restoring geomorphic and ecological processes in incised rivers: problems, criteria and approaches in the Northern Apennine (Italy)

Incised and degraded rivers pose a series of problems and challenges for their restoration and management. It is increasingly recognised that the geomorphic aspects assume a key role, particularly in projects with the main objective of restoring or promoting a more natural form and dynamic of the river. In this paper, we present a brief overview of a series of research projects (Ombrone and Pesa Streams in the Arno River catchment; Vara, Magra and Panaro Rivers) aimed to propose strategies conciliating flood risk and restoration objectives. All case studies are affected by similar problems, related for many aspects to a common morphological evolution of the channel. A strong human impact, due to a period of very intensive sediment mining and to many other disturbances and interventions (land use changes, dams, weirs, bank protections, etc.), is responsible for: (a) channel bed incision of variable intensity, but always very significant, and persistent conditions of sediment deficit; (b) progressive channel narrowing, related to the reduction in sediment transport and to bed lowering, and in some cases directly associated with artificial interventions. The physical degradation of these rivers has many negative consequences on habitats and ecosystems. The proposed strategies of management and restoration take into account the past channel evolution, and are compatible with the present trends of channel adjustments. In particular, the option of promoting channel recovery rather than morphological reconstruction is identified as the best strategy, being sediment load and stream power of these rivers sufficiently high.