We project climate-driven changes in flow and sediment partitioning across the Rhine delta using a hybrid one-dimensional model informed by two-dimensional sediment-partitioning data. Simulations spanning 150 years and 540 km show a continued shift of discharge toward the Waal branch, while the effects of historical interventions gradually diminish. Climate impacts on flow division emerge around 2050 and intensify thereafter: by 2150, the IJssel is projected to convey approximately up to 17% less discharge under low-flow conditions, whereas the Waal may receive up to 6% more. Although hydrograph changes have limited influence on flow partitioning, they markedly increase channel-bed erosion by coarsening the sediment flux delivered to the bifurcation region and enhanced sensitivity to shear-stress gradients across the bifurcation. Consequently, climate forcing, particularly sea-level rise, overtakes past interventions as the dominant driver of future flow partitioning and bed level adjustment. These results have direct implications for long-term water management, navigation, and ecological resilience in the Rhine delta.

This paper explores the mainstreaming and upscaling of Nature-Based Solutions (NbS) in Northwest Europe, focusing on experiences from the INTERREG ResiRiver project. It highlights key concepts such as NbS, mainstreaming, and upscaling, using case studies from nine pilot projects across Belgium, France, Germany, Ireland, and the Netherlands. The study applies the IUCN Global Standard for NbS to establish a baseline, emphasizing the importance of iterative assessments and co-benefit valuation. Challenges in governance, economic feasibility, and adaptive management are discussed. The paper concludes by advocating for robust communication strategies and international collaboration to accelerate NbS adoption.

Climate change is expected to increase the frequency and magnitude of river floods ¹. Floods not only cause damage by inundation and loss of life ^2,3 but also jeopardize infrastructure because of bank failure and riverbed erosion processes that are poorly understood. Common flood safety programmes include dyke reinforcement and river widening ^{4, 5, 6, 7, 8–9}. The 2021 flood in the Meuse Basin caused 43 fatalities and billions of dollars of damage to infrastructure ¹⁰. Here, on the basis of analysis of the Meuse flood, we show how uneven widening of the river and heterogeneity of sediment deposits under the river can cause massive erosion. A recent flood safety programme widened the river ¹¹, but created bottlenecks where widening was either prevented by infrastructure or not yet implemented. Riverbed erosion was exacerbated by tectonic uplift that had produced a thin top gravel layer above fine-grained sediment. Greatly enhanced flow velocities produced underwater dunes with troughs that broke through the gravel armour in the bottlenecks, exposing easily erodible sands, resulting in extreme scour holes, one more than 15 m deep. Our investigation highlights the challenges of re-engineering rivers in the face of climate change, increased flood risks and competition for river widening space, and calls for a better understanding of the subsurface.

Creating Resilient River Systems by Mainstreaming and Upscaling Nature-based Solutions or ‘ResiRiver’ for short, is an EU Interreg project focusing on the creation of Resilient River Systems through the mainstreaming and upscaling of Nature-based Solutions (NbS). Today, most North-West European (NWE) river systems face significant challenges, largely resulting from past anthropogenic riverine alterations (regulations and interventions) which have greatly exacerbated the negative effects of climate change like flooding and drought. These changes also put additional pressures on existing land-use-claims, and other societal/economic interests like shipping, agriculture and water quality and cause continued biodiversity-loss. In recent years, NbS have emerged as a novel and sustainable approach in river management, cap able of mitigating these threats while also strengthening climate resilience. They fit well within the EU’s ‘Blue Economy’ ambition and provide undeniable benefits for both human well-being and biodiversity. However, the widespread integration (mainstreaming) and implementation (upscal ing) of NbS in riverine systems has yet to become common practice. The ResiRiver project there fore aims to accelerate the upscaling and mainstreaming of NbS through a curated partnership of full-scale North West Europe NbS projects by gathering, transferring, and synthesizing know ledge and experiences, whilst ensuring that this is done at all relevant partner/national/EU levels.

This paper presents the outcomes of a learning needs assessment for upscaling and mainstreaming nature-based solutions in river systems. This study was undertaken as part of the EU Interreg NWE ResiRiver project (2023–2028) and provided insight in the Technology Readiness Levels and Societal Readiness Levels for nature-based solutions across The Nether lands, Germany, France, Belgium and Ireland. Furthermore, target audiences and learning needs were identified. The outcomes will be used to develop a learning platform and a tailor made training programme for the eleven organizations participating in ResiRiver and their direct partners in the process of implementing nature-based solutions in river systems.

Erosion-control measures in rivers aim to provide sufficient navigation width, reduce local erosion, or to protect neighboring communities from flooding. These measures are typically devised to solve a local problem. However, local channel modifications trigger a large-scale channel response in the form of migrating bed level and sediment sorting waves. Our objective is to investigate the large-scale channel response to such measures. We consider the lower Rhine River from Bonn (Germany) to Gorinchem (the Netherlands), where numerous erosion-control measures have been implemented since the 1980s. We analyze measured bed level data (1999–2020) around four erosion-control measures, comprising scour filling, bendway weirs, and two fixed beds. To get further insight on the physics behind the observed behavior, we set up an idealized one-dimensional numerical model. Finally, we study how the geometry and spacing of the measures affect channel response. We show that erosion-control measures reduce the sediment flux due to (a) lack of erosion over the measure and (b) sediment trapping upstream of the measure, resulting in downstream-migrating incision waves that travel tens of kilometers at decadal timescales. When the measures are in close proximity, their downstream effects may be amplified. We conclude that, despite fulfilling erosion-control goals at the local scale, erosion-control measures may worsen large-scale channel-bed incision.

Floods can cause punctuated changes to river channel morphology over short time scales. This work investigates whether spatial variation in river floodplain width drives enhanced morphodynamic change during floods. We examine the relationship between longitudinal variation in floodplain width and bed elevation change within and between flood events using high-resolution, biweekly bathymetry measurements from the Waal River, the Netherlands, over the last 20 years across a 10km study reach. We find that bed erosion during floods tends to occur just downstream of floodplain constrictions while deposition during floods tends to co-occur with spatial floodplain widening. Low flows show inverse bed elevation changes at the same locations resulting in a cyclic, along-channel variation in lowvs. high-flow bed elevation variation. This study suggests that spatial changes in planform channel geometry can help predict relative intra- and inter-flood morphodynamic changes.

Local river interventions, such as channel narrowing or side channels, are often necessary to maintain safety, ecology, or navigation. Such interventions have different effects on the river's bed morphology during periods of high- and low-discharge events. Mapping the bed-level variations for different discharge levels and understanding these effects can provide new opportunities for the design of interventions in multifunctional rivers. At any moment, the local bed level in a river is composed of bed-level changes that occur at various spatial and temporal scales. These changes consist of bed aggradation/degradation trends on a large scale, on an intermediate scale bed-level variations as a result of discharge fluctuations, and on small-scale moving river bed forms like dunes. Using the river Waal in the Netherlands as a case study, we analyze the intermediate-term bed-level changes resulting from discharge fluctuations (dynamic component) and propose adaptations to the design of floodplain interventions such that possible negative impact on the local bed-level changes is minimized. Time series of bed levels along two 10 km stretches of the case study are considered for a period of 16 years (2005–2020). Using a wavelet transform, we isolate bed-level variations resulting from discharge events. These bed-level variations are presented based on the magnitude of the discharge event and are compiled in an interactive atlas of river morphodynamics, allowing us to mitigate the impact of interventions. This will help river managers in the design of interventions and lead to improved management, operation, and maintenance of multifunctional rivers.

Tipping occurs when a critical point is reached, beyond which a perturbation leads to persistent system change. Here, we present observational indications demonstrating presently ongoing noise-tipping of a real-world system. Noise in a river system is associated with the changing flow rate. In particular, we consider the upper Rhine River delta, where flow and sediment fluxes are partitioned over the two downstream branches (bifurcates) of an important river bifurcation. Field observations show that a sequence of peak flows in the 1990s resulted in sudden sediment deposition in one bifurcate, triggering a persistent and ongoing change in the flow partitioning. This has caused the system to move toward an alternative equilibrium state or attractor. An idealized model confirms that a river bifurcation system under such conditions is prone to tipping, and provides insight on the onset of tipping.