Quantitative Assessment of Riverbed Planform Adjustments, Channelization, and Associated Land Use/Land Cover Changes: The Ingauna Alluvial-Coastal Plain Case (Liguria, Italy)

Abstract

The active-channel planform adjustments that have occurred along the Centa, lower Arroscia and lower Neva rivers since 1930, along with the riverbed channelization processes and the land-use and land-cover changes in disconnected riverine areas, were investigated through a multitemporal analysis based on remote sensing and geographical information systems (GIS). These watercourses flow through the largest Ligurian alluvial-coastal plain in a completely anthropogenic landscape. This research is based on the integrated use of consolidated and innovative metrics for riverbed planform analysis. Specific indices were introduced to assess active-channel lateral migration in relation to the active-channel area abandonment and formation processes. The Arroscia and Neva riverbeds experienced narrowing, progressive stabilization, and braiding phenomena disappearance from 1930 to the early 1970s, and then slight narrowing up to the late 1980s. Subsequently, generalized stability was observed. Conversely, the Centa was not affected by relevant planform changes. Recently, all rivers underwent a slight to very slight width increase triggered by the November 2016 high-magnitude flood. The active-channel adjustments outlined in this paper reflect the relevant role in conditioning the river morphology and dynamics played by channelization works built from the 1920s to the early 1970s. They (i) narrowed, straightened, and stabilized the riverbed and (ii) reduced the floodable surface over the valley-floor. Thus, large disconnected riverine areas were occupied by human activities and infrastructures, resulting in a progressive increase in vulnerable elements exposed to hydrogeomorphic hazards. The outlined morphological dynamics (i) display significant differences in terms of chronology, type, and magnitude of active-channel planform adjustments with respect to the medium- and short-term morphological evolution of most Italian rivers and (ii) reflect the widespread urbanization of Ligurian major valley floors that occurred over the 20th century. The outcomes from this study represent an essential knowledge base from a river management perspective; the novel metrics enlarge the spectrum of available GIS tools for active-channel planform analysis.

Spatiotemporal Characterization of the Urban Expansion Patterns in the Yangtze River Delta Region

“…Urban agglomerations are usually characterized by different population sizes [3], economic structures [4], landscape patterns [5], and road network densities [6,7]. These, together with many other factors, often result in a series of severe social and environmental problems [8] and geohydrological risks [9], ranging from increased temperatures [10,11] to polluted air [12], polluted water [13], and flood risk [14]. Around 1899, the urban expansion of Bamenda Town gradually invaded and transformed the hillside system, resulting in an increased dislocation of the relationship between human settlements and the environment [15].…”

Increased Riparian Vegetation Density and Its Effect on Flow Conditions

“…Due to these human interventions and climate change, the river channels and floodplains altered, and many of the fluvial processes accelerated [8][9][10][11][12][13][14]. In many rivers, the channel pattern changed from multithread or meandering to sinuous; the channel often incised and became narrower [15][16][17][18][19].…”

Integrated Approach for the Study of Urban Expansion and River Floods Aimed at Hydrogeomorphic Risk Reduction

“…Earth observation based on remote sensing and geographical information systems (GIS) is essential for the implementation of quantitative and qualitative analysis in these fields [41][42][43][44][45]. In particular, multi-temporal analysis of data retrieved from historical maps and aerial or satellite imagery, along with information on past floods, is fundamental to depicting the landscape evolution over time and possible flood scenarios [20,[46][47][48][49][50][51][52][53][54].…”