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)

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 in-channel sediment mobilization, bank retreats, and channelization structures collapses were surveyed. Furthermore, alluvial gullies, overbank deposits, crevasse splays, and surficial-erosion 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.

Automated summary

The study focused on the geomorphic response to the extreme flood of the lower Orba River in 2019, which caused severe damage to cultivated fields, structures, and infrastructures. Through post-flood field surveys, GNSS surveys, and aerial photography interpretation, geomorphic changes on the floodplain were mapped, and a specific legend for mapping flood-related and anthropogenic elements in a lowland agricultural landscape with regulated rivers was proposed.