The Ems Estuary faces existential challenges including flood risk, increasing turbidity, and biodiversity loss, all of which may intensify under future climate scenarios and require transboundary collaboration between the Netherlands and Germany. Addressing these challenges requires compliance with EU, national, and local regulations. Simultaneously each nation pursues socioeconomic benefits from the restoration through a holistic, system-based approach. This study synthesizes the key processes driving flood risk, hyper-turbidity, and salinization within the Ems Estuary. From this understanding the paper catalogues the planned and implemented pilot measures from both countries to advance their climate adaptation plans. Both nations share a common vision of leveraging the high turbidity of the estuary as an asset in climate adaption, e.g. for land raising, dyke reinforcement or habitat creation. Building on the pilot projects and shared visions, three transboundary upscaling strategies involving sediment management are proposed: (A) land elevation using dredged sediment; (B) multifunctional flood defences incorporating nature-based solutions; and (C) habitat creation and restoration to enhance ecological resilience. The Ems Estuary offers valuable insights for global transboundary estuarine management, illustrating how innovative sediment management and transboundary cooperation can be achieved to support climate adaptation and sustainable development. The study underscores the need for harmonized governance, standardized success metrics, and cross-border planning to enable effective upscaling.

Climate change (CC) is likely to affect the thousands of bar-built or barrier estuaries (here referred to as Small tidal inlets - STIs) around the world. Any such CC impacts on the stability of STIs, which governs the dynamics of STIs as well as that of the inlet-adjacent coastline, can result in significant socio-economic consequences due to the heavy human utilisation of these systems and their surrounds. This article demonstrates the application of a process based snap-shot modelling approach, using the coastal morphodynamic model Delft3D, to 3 case study sites representing the 3 main STI types; Permanently open, locationally stable inlets (Type 1), Permanently open, alongshore migrating inlets (Type 2) and Seasonally/Intermittently open, locationally stable inlets (Type 3). The 3 case study sites (Negombo lagoon – Type 1, Kalutara lagoon – Type 2, and Maha Oya river – Type 3) are all located along the southwest coast of Sri Lanka.
After successful hydrodynamic and morphodynamic model validation at the 3 case study sites, CC impact assessment are undertaken for a high end greenhouse gas emission scenario. Future CC modified wave and riverflow conditions are derived from a regional scale application of spectral wave models (WaveWatch III and SWAN) and catchment scale applications of a hydrologic model (CLSM) respectively, both of which are forced with IPCC Global Climate Model output dynamically downscaled to ~50 km resolution over the study area with the stretched grid Conformal Cubic Atmospheric Model CCAM. Results show that while all 3 case study STIs will experience significant CC driven variations in their level of stability, none of them will change Type by the year 2100. Specifically, the level of stability of the Type 1 inlet will decrease from ‘Good’ to ‘Fair to poor’ by 2100, while the level of (locational) stability of the Type 2 inlet will also decrease with a doubling of the annual migration distance. Conversely, the stability of the Type 3 inlet will increase, with the time till inlet closure increasing by ~75%. The main contributor to the overall CC effect on the stability of all 3 STIs is CC driven variations in wave conditions and resulting changes in longshore sediment transport; not Sea level rise as commonly believed.