Flood-induced ground effects and flood-water dynamics for hydro-geomorphic hazard assessment: the 21–22 October 2019 extreme flood along the lower Orba River (Alessandria, NW Italy)

Abstract

The knowledge of flood-induced ground effects and flood-water dynamics is a crucial issue for hydro-geomorphic hazards assessment and mapping, and thus for river management and land use planning. This paper and the related 1:15,000 map illustrate the lower Orba River (NW Italy) and its adjacent floodplain geomorphic response to the 21-22 October 2019 extreme flood. This was estimated to be a 500-years flood and caused severe damage to cultivated fields, structures, and infrastructures. The research is based on extensive post-flood field surveys, ante-and post-flood GNSS surveys, and aerial photographs interpretation. Intense inchannel sediment mobilization, bank retreats, and channelization structures collapses were surveyed. Furthermore, alluvial gullies, overbank deposits, crevasse splays, and surficialerosion evidences were mapped over the floodplain, along with the flooded area (17.65 km 2 ) and the flood-water features. A specific legend developed for flood-related and anthropogenic elements mapping in a typical lowland agricultural landscape with regulated rivers is proposed.

Semi-automatic mapping of shallow landslides using free Sentinel-2 and Google Earth Engine

“…Alluvial quaternary deposits occupy the bottom of the valley. Several small creeks cross the study area with S-N directions that, in the 2019 event, caused flash floods (Mandarino et al, 2021). The geomorphology of the area is characterized by the presence of a hilly landscape with a more steep slope in the Serravalle Formation, in the northern sector.…”

“…Several villages and the small town of Gavi are located inside the AOI, henceforth called Gavi area. The Castle of Gavi hill was particularly hit by shallow landslides, as also occurred in 2014, 1977and 1935events (Govi, 1978Mandarino et al, 2021). Historical information tells us that the Liguria region and NW Alps have been affected by several extreme rainfall events, usually during autumn (D'Amato Avanzi et al, 2015;Cevasco et al, 2014;Ferrari et al, 2021;Roccati et al, 2018;Guzzetti et al, 2004;Luino, 1999).…”

“…Also, deeper landslides were triggered, like in the case of the villages Monesi di Mendatica, which were partly destroyed by such kind of landslide (ARPA Piemonte, 2018; Notti The October to December 2019 period has been characterized by numerous meteorological events that hit NW Italy, 125 causing an extreme rainy period (Copernicus Climate Change Service, 2019). In particular, on 19-21 October 2019, an extreme rainfall event hit an area between Liguria and Piemonte region, causing severe floods and diffuse shallow landslides in the basins of the Orba and Bormida rivers (Mandarino et al, 2021). This event was caused by a semistationary V-shape storm over a relatively small area with extreme rainfall (Figure 2 C) both in intensity and quantity (Mercalli, 2019).…”

VGI and Satellite Imagery Integration for Crisis Mapping of Flood Events

“…These types of applications have already been exploited in, e.g., archaeological studies [41,42], management of heritage assets and infrastructure [43][44][45], cataloguing of agricultural spaces [46], and environmental issues [47,48]. Examples of their use in studies on natural risks, such as landslides [49,50], earthquakes [51] and floods [52,53], were presented in the literature as well.…”

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

“…Several studies have identified their main causes to be severe human pressures, both at the basin and channel scale, namely in-channel sediment quarrying [4,[19][20][21][22], dam closure [19,[23][24][25][26], channelization [27][28][29], and land use changes [30][31][32]. These interventions, associated with a general economic growth, caused river systems to experience landform simplification, and thus the loss of habitats [9,14,15,33,34], geomorphological instability and related damage to in-channel structures [14,19,33,[35][36][37], as well as floodable area reduction and progressive occupation of the areas of fluvial pertinence [14,27,38]. As a result, serious issues in terms of environmental quality, biodiversity conservation, and hydrogeomorphic hazards and risks arose.…”