Human infrastructure fragments river-to-coast and alongshore sediment connectivity at the global scale

Abstract Coastal erosion is a growing global concern, largely driven by sediment supply deficits, sea-level rise, and changing wave climates. While the role of engineering infrastructure in disrupting sediment connectivity has been well recognized locally, no global-scale assessment has yet quantified how dams and jetties jointly fragment pathways from rivers to coasts and alongshore. Here we develop a global diagnostic framework that balances riverine sand supply and wave-driven longshore transport along quasi-regular coastal transects. Using standardized scenarios, we simulate the impacts of (i) sediment trapping by dams and (ii) interruption of longshore transport by jetties, applied in a static diagnostic mode to isolate their respective and combined effects. Our results show that dams reduce riverine sand delivery by an average of 15%, with declines exceeding 25% in tropical South America, Central Africa, and Southeast Asia. Jetties exert more localized but stronger effects, generating sediment budget shifts of up to ±2 Mt/yr and reducing transport cell lengths by more than 500 km in severely affected coastlines such as Brazil, Angola, and Indonesia. Together, these drivers fragment sediment pathways, creating new hotspots of deficit in densely populated and morphologically sensitive regions. By demonstrating how human infrastructure alters sediment continuity at a planetary scale, this study highlights the need for global sediment governance, defined here as coordinated strategies to preserve sediment fluxes across rivers and coasts, as a foundation for long-term coastal resilience and effective adaptation planning.