Channel adjustments in northern and central Italy over the last 200 years

Abstract

This paper deals with channel evolution over the past 200 yr in 12 selected streams in northern and central Italy and aims at reconstructing the evolutionary trends (e.g., trends of channel width and bed elevation) and understanding the causes of channel adjustments. The selected streams have been studied using various sources and methods (historical maps, aerial photographs, topographic surveys, and geomorphological surveys). The selected rivers have undergone almost the same processes in terms of temporal trends; however, the magnitude of adjustments varies according to several factors, such as original channel morphology. Initially, river channels underwent a long phase of narrowing (up to 80%) and incision (up to 8–10 m), which started at the end of the nineteenth century and was intense from the 1950s to the 1980s. Then, over the last 15–20 yr, channel widening and sedimentation, or bed-level stabilization, have become the dominant processes in most of the rivers. Different human interventions have been identifi ed as the causes of channel adjustments in Italian rivers (sediment mining, channelization, dams, reforestation, and torrent control works). Such interventions have caused a dramatic alteration of the sediment regime, whereas effects on channel-forming discharges have seldom been observed. Some notable implications for river management and restoration are (1) the state of rivers before major human disturbances and channel adjustments can rarely be taken as a reference, as at present rivers are far from their pristine condition; and (2) sediment management is and will be a key issue in such fl uvial systems

Channel adjustments and alteration of sediment fluxes in gravel‐bed rivers of North‐Eastern Italy: potentials and limitations for channel recovery

“…Likewise, there are no evidences that floods determined the end of the major narrowing phase. Except for the Cellina torrent (a 20-year flood event occurred in 2002), very large events (RI > 10-15 years) have not occurred in the last 15-20 years (Surian, 2006;Surian et al, 2009). However, we believe that if sediment fluxes undergo less dramatic alterations in the future, a major role in the adjustment of channel morphology will be played by the occurrence of large flood events, as well as by vegetation growth rates (Hicks et al, 2008).…”

“…Average rates of recent channel widening have varied between 4 m year À1 (e.g. upper Brenta) and 13 m year À1 (lower Piave) (Surian et al, 2009), from which we can anticipate that bank erosion will be exhausted within a few decades (see Figure 4), except where a very wide erodible corridor still exists (e.g. along the upper Tagliamento).…”

Erosion in Mediterranean landscapes: Changes and future challenges

“…Bed degradation and the development of bed armouring and channel narrowing have been detected in several tributaries in the Rhône basin Piégay, 2001, 2002), and in Pyrenean rivers (Beguería et al, 2006), whereas some Italian rivers underwent a change from braiding toward single-thread channels (Surian et al, 2010;Comiti et al, 2011), with extensive streambed degradation threatening the stability of infrastructure, as has occurred in the Arno River (Billi and Rinaldi, 1997) Mediterranean deltas have also been destabilized by the construction of large reservoirs, which behave as sediment traps, reducing sediment transfer towards the sea (Tena et al, 2011).…”

Geomorphology of the Lower Calore River alluvial plain (Southern Italy)

“…Italian rivers underwent marked channel adjustments in the last century, mainly consisting of incision and narrowing (Surian et al, 2009;Surian & Rinaldi, 2003). In particular, the Calore River (Southern Italy) experienced a mean narrowing of 66% (with a peak of 86%) and an incision of the order of 3-4 m between 1955 and 1998 (Magliulo, Valente, & Cartojan, 2013).…”

“…In particular, the Calore River (Southern Italy) experienced a mean narrowing of 66% (with a peak of 86%) and an incision of the order of 3-4 m between 1955 and 1998 (Magliulo, Valente, & Cartojan, 2013). Most researchers suggest human disturbances such as gravel mining, river damming, channelization, floodplain alterations and land-cover and land-use changes in the basin as the main causes of medium-and shortterm channel adjustments (Gregory, 2006;Hooke, 2006;Piacentini, Urbano, Sciarra, Schipani, & Miccadei, 2015;Surian et al, 2009;Surian & Rinaldi, 2003). These factors act together with natural control factors, such as climate change (Knox, 1993;Rădoane, Obreja, Cristea, & Mihailă, 2013;Starkel, 2002).…”