Brenna et al. (2026) The great decline of suspended sediment load in the Po River (Italy) over the last 100 years

Identification

• Journal: CATENA
• Year: 2026
• Date: 2026-01-30
• Authors: Andrea Brenna, Simone Bizzi, Nicola Surian
• DOI: 10.1016/j.catena.2026.109864

Research Groups

• Department of Earth Sciences “A. Desio”, University of Milan, Milano, Italy
• Department of Geosciences, University of Padua, Padova, Italy

Short Summary

This study investigated the profound, asynchronous reduction in suspended sediment load in the Po River over the last century, linking it to human impacts like damming, in-channel mining, land-use changes, and river training works, which have significantly altered the river's geomorphology and delta stability.

Objective

• To investigate how a sequence of human impacts has profoundly altered suspended sediment yields in the Po River, the largest fluvial system in Italy, over the last 100 years, by integrating long-term data with detailed analysis of anthropogenic drivers to reconstruct the spatiotemporal trajectory of sediment dynamics and inform integrated management strategies for delta restoration.

Study Configuration

• Spatial Scale: Po River (Italy), the largest fluvial system in Italy, extending 651 km, encompassing a drainage area of 75,000 km². Focus on the middle course (Piacenza section, 42,030 km² drainage area) and lower course (Pontelagoscuro section, 70,090 km² drainage area), and the delta region. Specific river stretch between the confluences of the Adda and Mincio rivers (123 km).
• Temporal Scale: Long-term analysis over 100 years (1924–2019), with specific periods of focus: 1924–1943, 1956–1991, and 2010–2019.

Methodology and Data

• Models used: Empirical relationship for delta area estimation (Syvitski and Saito, 2007). Statistical analysis including linear and polynomial regressions, and Least Significant Difference multiple range testing.
• Data sources:
  • Long-term daily suspended sediment concentration and water discharge data (1924–2019) from Hydrological Annals (National Hydrological Service, Emilia-Romagna Regional Environmental Agency - ARPAE) at Piacenza and Pontelagoscuro stations.
  • Historical land-use data for Northern Italy (1934–2007) from the Italian National Institute of Statistics (ISTAT), synthesized by Niedertscheider and Erb (2014).
  • Dam and reservoir construction data from the Italian Ministry of Infrastructure and Transport and prior studies.
  • Historical documentation of river training schemes (1930s–1950s) from Gorio (1953) and subsequent reviews.
  • Aerial imagery (1954 "Volo GAI", 2006 National Geoportal of Italy) for mapping deactivated active channel areas.
  • Topographic cross-sections (1954, 2005) from the Geoportal of the Interregional Agency for the Po River (AIPO) for estimating depositional body thickness.
  • Sediment cores (10 cores at 4 sites) for grain-size analysis using a Mastersizer 3000 laser granulometer.

Main Results

• No clear long-term trends were observed in water discharge (maximum, mean, and total flow rates) at Piacenza and Pontelagoscuro gauging stations over the 1924–2019 period.
• The Po River experienced a substantial long-term reduction in annual suspended sediment yields (SSY) and concentrations (SSC) over 1924–2019, exceeding -85% at Piacenza and -72% at Pontelagoscuro.
• The decline in suspended sediment transport occurred asynchronously:
  • At Piacenza (middle course), a marked decline of -48% in SSY and -54% in SSC occurred during 1924–1943, primarily driven by extensive dam construction in the western catchment.
  • At Pontelagoscuro (lower course), SSY remained relatively stable initially, followed by a strong decrease of nearly -50% in SSY and -48% in SSC during 1956–1991. This was largely influenced by river training interventions (promoting sediment deposition behind groynes) and sediment retention in flood detention basins along Apennine tributaries.
• The total volume of sediment trapped behind navigation structures (groynes) between the Adda and Mincio rivers is estimated at 96.1 ± 16.8 million cubic meters (Mm³), with approximately half (48 ± 8.4 Mm³) consisting of silt.
• The estimated volume of trapped silt (48 ± 8.4 Mm³) is consistent with the calculated "missing" suspended sediment load (37 Mm³) at Pontelagoscuro during 1956–1991, suggesting these structures captured approximately 18% of the river's yearly suspended sediment load.
• The ongoing decline in SSY at Pontelagoscuro in the 2010s (annual SSY < 5 Mton) is attributed to the progressive increase in forest cover at the basin scale and the continued construction of dams and flood detention basins along Apennine tributaries.
• The century-long decline in wash-load has contributed to significant geomorphological transformations in the Po delta region, hindering its ability to accrete and compensate for subsidence and sea-level rise, leading to an unfavorable prognosis for its long-term stability.

Contributions

• Provides a comprehensive, century-long spatiotemporal reconstruction of suspended sediment dynamics in the Po River, a major European fluvial system.
• Quantifies the asynchronous and cumulative impacts of multiple anthropogenic drivers (damming, river training works, land-use changes, flood detention basins) on riverine sediment transport.
• Identifies and quantifies the significant role of anthropogenically induced sediment traps (e.g., behind navigation groynes) in sequestering fine sediments from downstream transfer.
• Offers critical insights for integrated river management strategies, proposing the reactivation of considerable volumes of trapped sediment as a promising, albeit complex, strategy for delta restoration and mitigation of sediment deficits.
• Quantitatively assesses the potential for sediment reintroduction to restore a more balanced morpho-sedimentary regime in the Po delta, increasing its theoretical area and vertical accretion rates.

Funding

• University of Padova (DOR funds)
• Autorità di bacino distrettuale del Fiume Po
• Project “The Geosciences for Sustainable Development” (CUP C93C23002690001)

Citation

@article{Brenna2026great,
  author = {Brenna, Andrea and Bizzi, Simone and Surian, Nicola},
  title = {The great decline of suspended sediment load in the Po River (Italy) over the last 100 years},
  journal = {CATENA},
  year = {2026},
  doi = {10.1016/j.catena.2026.109864},
  url = {https://doi.org/10.1016/j.catena.2026.109864}
}