Engineered river systems, such as the Lower Rhine, are currently facing pressures from historical channelisation and projected climate change, which, together, exacerbate issues such as channel bed incision and skewed discharge partitioning at bifurcations (Ylla Arbós, 2021; Blom, 2024). In response to these challenges, Rijkswaterstaat is currently exploring various large-scale intervention strategies under the new Room for the River 2.0 programme. To determine how robust these interventions remain under future climate scenarios characterised by increased hydrograph variability and sea level rise, river management requires simulating large-scale measures, such as Longitudinal Training Walls (LTWs) with or without side channels, and floodplain lowering, over a centennial timescale. While one-dimensional (1D) models have been successfully employed for long-term simulations of the Lower-Rhine (Ylla Arbós, 2023; Chowdhury, 2025), they rely on nodal-point relations, of which the formulation contains challenges to adequately capture critical 2D/3D flow structures, lateral morphological changes, and complex bifurcation feedback mechanisms that influence the discharge partitioning in the system. As an alternative, we consider two-dimensional (2D) depth-averaged morphodynamic modelling. However, applying high-resolution 2D models over large spatial domains (~400 km) for century-long periods presents a computational bottleneck.

The Rhine River system has been shaped by human interventions for centuries, making it one of the most engineered river networks in Europe. Issues such as ongoing channel bed incision and changes in hydrograph due to climate change (Arbos et al., 2023) are anticipated to significantly affect future river functions, including flood safety, freshwater supply, and inland shipping. In recent decades, large-scale projects such as “Room for the River,” the installation of longitudinal training walls, and sediment nourishments have helped preserve the Rhine’s functionality. At the Pannerdense Kop bifurcation, where the Dutch upper Rhine divides flow and sediment between the Waal and the Pannerden Canal, a gradual change in flow division between the branches is observed (Chowdhury et al., 2023). This change appears to be linked to a series of peak flow events in the 1990s, which resulted in sediment deposition in one bifurcate, setting off a slow shift in flow partitioning ever since. More recently, Blom et al. (2024) proposed that the extreme flows in the 1990s might have pushed the system toward a tipping point and an emerging alternative equilibrium state. Ensuring the anticipated flow partitioning is crucial not only for maintaining water supply and navigability during low-flow periods but also for controlling flood risk during peak events.