Alteration of gravel-bed river morphodynamics in response to multiple anthropogenic disturbances: Insights from the sediment-starved Parma River (northern Italy)

A width‐based approach to estimating historical changes in coarse sediment fluxes at river reach and network scales

“…Our results underscored that the anthropic pressures affecting the Po catchment, with the maximum rates occurring from the 1950s to the 1980s (Parrinello et al, 2021), induced average decreases of −19% and −30% in coarse sediment fluxes along the Po River and the terminal sectors of its tributaries, respectively, over the period 1954–1998. This decrease in bed material load, as stated by Church (2006), can be regarded as the main driver of the morphological changes described in detail by several authors (e.g., Brenna et al, 2021; Clerici et al, 2015; Gumiero et al, 2015; Mandarino et al, 2019; Surian & Rinaldi, 2003) for a number of rivers of the Po catchment. The lower reduction in coarse sediment fluxes estimated for the last two decades (i.e., 1998–2020) is consistent with the decrease in human pressures on the Po River network in recent years, suggesting that some portions of the system are still responding to human disturbances, whereas others are undergoing a degree of morphodynamic recovery.…”

“…Available scattered evidence suggests that during such period, the volume of sediment mined yearly from the Po River was between one and two orders of magnitude higher than the supposed bed material load in the site (Dal Cin & Simeoni, 1990; Parrinello et al, 2021). Over the last three decades, the human pressures on several Italian rivers have slightly decreased, likely increasing sediment availability in these streams (Bollati et al, 2014; Brenna et al, 2021; Gurnell et al, 2009; Mandarino et al, 2020; Surian, Rinaldi, et al, 2009).…”

“…From a morphological point of view, researchers documented how the Alpine (e.g., Pellegrini et al, 2008; Siviglia et al, 2004) and the Apennine (e.g., Brenna et al, 2021; Clerici et al, 2015; Gumiero et al, 2015; Mandarino et al, 2019) tributaries of the Po River have responded to human‐induced sediment starvation. They identified three main types of morphological responses, with maximum rates occurring over the 1960s to the 1990s: bed level lowering (incision ranging from a few metres up to more than 10 m), channel width reduction (a narrowing of up to 50% or more) and changes in planform morphological configuration (evolution from braided to wandering or single‐thread channels).…”

“…They identified three main types of morphological responses, with maximum rates occurring over the 1960s to the 1990s: bed level lowering (incision ranging from a few metres up to more than 10 m), channel width reduction (a narrowing of up to 50% or more) and changes in planform morphological configuration (evolution from braided to wandering or single‐thread channels). From the 2000s to the present, an inversion of the evolutionary trajectory characterizes some tributaries of the Po River as showing moderate widening and recovery of morphological complexity (e.g., Bollati et al, 2014; Brenna et al, 2021; Mandarino et al, 2020). This recovery was attributed to both an increase in sediment availability due to the cessation of intense in‐channel mining after the 1980s (Bollati et al, 2014) and a more frequent occurrence of high‐magnitude floods over the last three decades (Clerici et al, 2015) that is related to on‐going climate changes (Blöschl et al, 2020; Gaume et al, 2016).…”

“…Several works analysed the morphological responses of fluvial systems to reductions in sediment supply (e.g., Church, 1995; Graf, 2006; Surian & Rinaldi, 2003) and identified three main effects: bed‐level incision, channel narrowing and changes in planform morphological configuration. Fewer studies have focused on anthropic intervention‐induced alterations in sediment fluxes, likely because of the aforementioned limitations in sediment transport estimation (Arnaud et al, 2015; Brenna et al, 2021; Preciso et al, 2012; Surian & Cisotto, 2007; Vázquez‐Tarrío et al, 2019; Vericat & Batalla, 2006). Even less quantification has been directed to these changes over expansive time and spatial scales (e.g., the last century and a large river network, respectively).…”