EGU22-6894
https://doi.org/10.5194/egusphere-egu22-6894
EGU General Assembly 2022
© Author(s) 2023. This work is distributed under
the Creative Commons Attribution 4.0 License.

Rapid formation of a bedrock canyon following gravel mining in the Marecchia River, Northern Apennines. 

Manel Llena1, Tommaso Simonelli2, and Francesco Brardinoni1
Manel Llena et al.
  • 1University of Bologna, Department of Biological, Geological and Environmental Sciences, Italy (manel.llena@unibo.it)
  • 2Autorità di Bacino Distrettuale del Fiume Po, Parma, Italy.

River canyons are characteristic features of transient fluvial systems responding to perturbations in base level and/or sediment supply. Investigating the dynamics of canyon formation and development is challenging due to the typically long time scales and the possible experimental confounding involved. In this context, the lower portion of the Marecchia River, with a history of gravel mining on alluvial deposits resting on highly erodible (i.e., claystones and poorly consolidated sands) bedrock, offers the opportunity to set up a natural experiment and investigate the onset of canyon incision and its subsequent stages of development across five decades (1955-1993). To these ends, we evaluate decadal geomorphic changes of 10-km valley segment of the Marecchia River between Ponte Verucchio and Rimini (Northern Italy) through analysis of Digital Elevation Models derived from the application of Structure from Motion to archival aerial imagery (i.e., 1955, 1969, 1976, 1985, 1993) and from a reference-LiDAR survey (i.e. 2009), in conjunction with analysis of planimetric changes in active channel width and lateral confinement.

During the 1955-2009 period, fluvial incision led to the formation of a 6-km canyon, with average vertical incision of about 15 m (in places exceeding 25 m) and a corresponding annual knickpoint migration rate of about 100 m/yr. In volumetric terms, canyon formation and evolution has involved 6.1 106 m3 (95%) of degradation and 0.29 106 m3 of aggradation (5%), with a corresponding net volume loss of 5.8 106 m3. As a result of canyon development, the active channel has narrowed by about 80%, and channel pattern has drastically changed from braided unconfined to single-thread tightly confined one. These processes were especially important during the 1955-1993 period. Since 1993 to the present, main channel is characterized by a general stability of the active channel width with evidences of a slight recovery through mass wasting processes within it. Local disturbance associated with ongoing canyon development have propagated and are still propagating upstream, posing immediate threat to infrastructures.

How to cite: Llena, M., Simonelli, T., and Brardinoni, F.: Rapid formation of a bedrock canyon following gravel mining in the Marecchia River, Northern Apennines. , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6894, https://doi.org/10.5194/egusphere-egu22-6894, 2022.