Morphological response to river engineering and management in alluvial channels in Italy

Abstract

In response to various types of human disturbance, most Italian rivers have experienced considerable channel adjustment during the last centuries and in particular in the last decades. This paper reviews all existing published studies and available data, and aims to reconstruct a general outline of the main channel adjustments that have occurred in Italian rivers during the past 100 years.Two main types of channel adjustment have been recognized: (a) incision, which is commonly on the order of 3 -4 m, but in some cases is even more than 10 m; (b) narrowing, with channel width reduction up to 50% or more. In some reaches, these adjustments have led to changes in channel pattern in particular from braided to wandering.Such channel adjustments are due to several types of human intervention, particularly sediment extraction, dams and channelization. A strong temporal relationship (specifically, short reaction times) between human disturbance and channel adjustment can be inferred, but trends of adjustment are available for only a few rivers (e.g. the Po, the Arno and the Piave Rivers). These trends show that incision and/or narrowing are more intense immediately after the disturbance and then slow and become asymptotic; the same trends also suggest that larger rivers could have longer relaxation times.The results of this study are synthesised in a general classification scheme that summarises the main styles of adjustment observed in Italian rivers. According to the scheme, braided rivers adjust through prevalent narrowing with varying rates of incision, whereas single-thread rivers adjust mainly through a more pronounced incision accompanied by various amounts of narrowing. The scheme, representing initial and final (present) morphologies and not including intermediate stages of channel adjustment, will need to be tested on the basis of more detailed data to have a wider application both to the Italian context and to fluvial systems elsewhere, affected by similar types of human disturbance causing a reduction of sediment supply. D

Network response to disturbances in large sand-bed braided rivers

“…It could also result in fixation of bars (Wu and Yeh, 2005). At the same time, Rahman et al (2012b) and Takagi et al (2007) demonstrated that the bank erosion along the braidplain is linked to bar dynamics, as mid-channel bars steer the flow towards the braidplain banks. Bank erosion is also an important sediment source for mid-channel bars (Xu, 1997;Ahktar et al, 2011).…”

“…A third group of studies applied statistical analyses and metrics based on regime theory to describe the long-term effects of river engineering and human interferences on rivers. Commonly used metrics are, for example, mean channel width and longitudinal slope (e.g., Church, 1995;Brandt, 2000;Surian and Rinaldi, 2003;Ronco et al, 2010). However, these studies have not addressed the short-term response of bars and branches on the long-term equilibrium conditions.…”

Riverbank changes along the Mekong River: Remote sensing detection in the Vientiane–Nong Khai area

“…As a consequence, channel stability is often threatened (Fuller et al, 2003;Grant et al, 2003;Kesel, 2003;Rinaldi, 2003). Such human activities could be stronger forces for change than natural events such as floods, droughts and landslides (Surian and Rinaldi, 2003). These human-induced channel changes may result in various environmental and socialeconomic consequences in navigation, loss of riparian land and infrastructure, flood hazard and the alteration of aquatic and riparian ecosystems.…”

Multi-Temporal Image Analysis for Fluvial Morphological Characterization with Application to Albanian Rivers

“…Narrowing of the active river corridor may also negatively affect the hydraulic safety of human communities with respect flooding risk, because a narrowed river corridor determines higher water levels during floods. River narrowing is also often accompanied by riverbed incision [48], which has often resulted in much increased damage for river structures like bridges, levees and check dams.…”

“…River width variability has often been observed at relatively slow time scales (decades [48]), and it is therefore very important to develop tools that allow tracking such changes over the relevant time scales, and across a variety of geographical contexts characterized by different paths of data source availability. A complementary ingredient for effective environmental management would be to understand the causes and controls of those evolutionary river trajectories.…”