Harnessing Natural Land-Building Processes in Human-Dominated River Deltas: Lessons from the Po River Delta (Italy)

Continued increases in climate extremes, population growth, natural and human-induced subsidence present a significant threat to the sustainability of many of the world’s river deltas. Hard engineering solutions, such as dikes and river embankments designed to prevent flooding in reclaimed deltaic regions, are proving increasingly unsustainable and may undermine the long-term resilience of deltaic ecosystems.

This challenge is particularly pressing in highly human-modified river deltas, where vast expanses of land have been reclaimed in the past. The combined impact of subsidence, climate change-driven sea-level rise, and intensified storm surge events is exposing reclaimed areas to a growing risk of flooding, saltwater intrusion and soil salinization. These processes will ultimately lead to a devaluation of reclaimed lands, making the continuous maintenance of levees and pumping systems, required to keep these areas dry, economically unfeasible. As a result, when the cost of sustaining reclaimed land outweighs its economic value, abandonment becomes the more likely outcome. Once these low-lying areas are abandoned, they become increasingly vulnerable to dike and levee failure, re-exposing them to natural fluvio-deltaic morphodynamic processes.

In this study, we use Italy’s heavily modified Po River Delta as a case study to illustrate these dynamics. We focus specifically on the seaward-most portion of the subaerial delta topset, where the failure of dikes protecting a previously reclaimed area known as “Isola della Batteria” led to the rapid infill of the area by river-borne sediment and to the formation of approximately 30 hectares of new emergent wetlands within just 30 years.
By integrating field data and remote sensing techniques—including sediment core analyses, UAV LiDAR surveys, ground-based topographic measurements, satellite-derived subsidence rates, historical aerial imagery and topo-bathymetric maps—we reconstruct the morphological evolution of the area over the past 50 years. We then use these data to calibrate a morphodynamic numerical model, which we apply at multiple locations within the Po River Delta to assess the feasibility of managed realignment strategies aimed at creating new wetland habitats of significant ecological and socio-economic value.

Our findings highlight the potentials of controlled dyke-breaching interventions in highly human-modified delta systems characterized by extensive reclaimed land. Such strategies enhance sediment retention on delta plains, promoting vertical accretion at rates that easily exceed projected relative sea-level rise. This process supports the rapid formation of new deltaic wetlands, ultimately strengthening the resilience of deltaic ecosystems as a whole.

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.