Geomorphological Approaches for River Management and Restoration in Italian and French Rivers

Abstract

River management and restoration in Italy and France are increasingly considering physical processes and trends of channel adjustment as a basic knowledge for enhancing river conditions and promoting channel recovery. Italian and French rivers are characterized by a long history of human disturbances and land use changes. As a consequence, trends of channel adjustments and related management problems are similar, with a historical phase of aggradation followed by a period (last century) of intense channel incision and narrowing. A general overview on recent progress in using geomorphic approaches to river management in Italy and France is presented here by illustrating a series of examples of studies and management applications. A synthetic state of the art on the recent morphological changes of Italian and French rivers is first reported. Some examples of quantification of bed load are also illustrated, providing a necessary quantitative knowledge for possible interventions or strategies for promoting bed load recovery. Finally, examples are provided to illustrate how an understanding of geomorphic processes is used to define regional visions and associated tools for planning and targeting actions and to promote sustainable actions from local to catchment scale.

Channel adjustments and vegetation cover dynamics in a large gravel bed river over the last 200 years

“…As discussed above, gravel mining is the main driver of incision and narrowing during this phase, and vegetation encroachment is a consequence of incision. This confirms the key role of sediment mining in Italian rivers (Surian et al, 2009a) and highlights some differences with other Alpine regions where afforestation in the floodplains (following changes in the land use) is considered, along with sediment mining, a major cause of channel incision (Liébault and Piégay, 2002;Rinaldi et al, 2010).…”

“…Again, the comparison with alpine rivers in southeastern France is of great value. In French rivers a widespread channel recovery was not observed, probably because after the main phase of incision (peaking in the 1970s) the river channels are still adjusting to the decrease of sediment supply from catchment afforestation (Liébault and Piégay, 2002;Rinaldi et al, 2010). On the contrary, the Piave River in the study reach underwent a remarkable morphological recovery (mainly by widening) thanks to the sediment input from the tributaries once the major degrading factor, i.e., gravel mining, ceased.…”

“…However, also the milder climate following the Little Ice Age might have contributed to a natural reduction of sediment supply and thus, partly, to channel narrowing. We do not have evidences that this phase of narrowing was associated with bed incision, therefore it is possible that narrowing occurred without incision, as shown in several French rivers (Liébault and Piégay, 2002;Rinaldi et al, 2010), or, alternatively, that very slight incision occurred, as documented in some Italian rivers Rinaldi, 2003, 2004).…”

A methodological framework for hydromorphological assessment, analysis and monitoring (IDRAIM) aimed at promoting integrated river management

“…The awareness that a river follows a complex evolutionary trajectory, reflecting a combination of long-term trends and short-term fluctuations driven by both natural and human controls, implies that in most cases the 'recovery' to an historical or 'pristine' state cannot take place due to completely changed boundary conditions (Dufour and Piégay, 2009). Consequently, the identification of a morphological 'reference state', which is difficult to define in fluvial systems with a long history of human impact, should be avoided when setting restoration goals (Kondolf et al, 2007;Rinaldi et al, 2011). It is more appropriate to define target conditions (e.g.…”

“…A sediment budget can be attempted by various approaches, including the morphological method (e.g., Ashmore and Church, 1998;McLean and Church, 1999;Ham and Church, 2000;Brewer and Passmore, 2002) or by estimating sediment transport capacity (e.g., Rinaldi et al, 2009Rinaldi et al, , 2011.…”