Nature-based solutions for resilient deltaic coasts: an example from a crevasse delta in the Po River Delta (Italy)

Delta plains are vulnerable environments, chiefly due to their low elevation, occurrence of highly dynamic depositional processes, high population density and anthropogenic pressure, and threats coming from climate change, more extreme weather events and accelerating rates of relative sea-level rise. Anthropic activities and interventions, typically aimed at reclaiming deltaic lands for agricultural, urban, and industrial purposes, have significantly modified the hydro-morphodynamic behavior of fluvio-deltaic environments, making the reclaimed land hydrologically disconnected from the river and starving natural wetlands of sediments.

A paradigm change in river-delta management plans is currently underway, from hard infrastructures to new approaches designed to “work with the river”, leading to a broad interest in so-called “nature-based” solutions to restore and create new deltaic lands.

The Po River Delta represents a prominent example of a strongly engineered deltaic system with compromised long-term sustainability. This work focuses on a crevasse delta recently formed in an abandoned and flooded embanked area in the Po Delta, which demonstrates that natural deltaic dynamics can occur also in strongly anthropogenically-modified deltaic plains and effectively build new emerged land. We used field analyses (collection of sediment cores with a hand auger corer) and remotely sensed data to characterize the sedimentary facies and morphosedimentary structure of the crevasse delta.

The study area was reclaimed and used through the 1950s and 1970s for agriculture. In the mid-1970s, levee breaching caused seawater inundation, after which the area was abandoned and partially colonized by reeds. The reclaimed land was hydrologically disconnected from the river and eventually sea level rise and subsidence caused the flooding of the entire area, evidenced in the stratigraphy by a laterally persistent serpulid-rich marker horizon. This situation, with only fine grained sediments deposited from suspension and bioturbation, persisted until 1999-2000, when a fluvial flood caused a natural breaching in the levees and re-establishment of natural deltaic processes and wetlands, with the formation of intertidal and vegetated crevasse delta lobes.

Through the sedimentological analysis of drilled cores, aerial and satellite images and their mutual correlation, this work aims to define and reconstruct the architecture and the morphosedimentary evolution of this crevasse delta, improving our knowledge of natural systems resilience: by reconnecting the river to its wetlands, we can reduce land loss and restore deltaic coasts by harnessing their land-building capacity.

This work is part of the research project “Ensuring resilience of the Po River Delta to rising relative sea levels using nature-based solutions for building land and mitigating subsidence (NatResPoNΔ)”, a PRIN 2022 PNRR project funded by the European Union – NextGenerationEU.