In July of 2021, large areas in the catchment of the Meuse River in Belgium, the Netherlands and Germany were affected by extreme rainfall and floods. This paper presents the hydraulic and morphological data that were collected during and after the flood. The data were analysed to understand the hydraulic and morphological functioning of the Meuse River in the Netherlands during the flood event. The data showed that measured peak discharges in the upstream part of the Meuse and regional tributaries were the highest ever recorded. However, as the flood had a very short duration, peak attenuation played an important role, resulting in discharges and water levels in downstream reaches that were lower than during previous floods. Furthermore, the implementation of river widening and floodplain lowering measures as part of the Meuse Works programme contributed to a reduction in peak water levels along the Meuse. The analysis also showed that flood forecasts in the upstream part of the Meuse in the Netherlands depended heavily on rainfall forecasts and rainfall-runoff modelling and underestimated the peak water levels up to 36 hours before the flood actually peaked. Further downstream, the lead time increases and forecasts are based on discharge levels that are measured in upstream parts of the catchments. This results in more accurate estimates. The floods have also resulted in unprecedented morphological changes. The armour layer in the riverbed of the ‘Common Meuse’, consisting of very coarse gravel, was mobilised and layers of fine sand quickly eroded. This resulted in multiple scour holes with depths of 3 to 15m, especially in a reach which was hardly or not at all widened in the room for the river programme called Meuse Works. In this reach, the flow velocities were high and even higher than prior to the Meuse Works.@en

Door klimaatverandering verandert het afvoerregime van onze grote rivieren. Hoogwaters worden hoger en frequenter, laagwaters lager en langduriger. Hoe we daarop reageren hangt af van hoe we klimaatverandering zien: als opgave, of als kans om onvolkomenheden aan te pakken. In dit artikel presenteren we aanzetten voor een meer geo-ecologisch gefundeerde inrichting, of – naar McHarg – voor design with nature. Climate change is expected to significantly influence the discharge regime of the Rhine and Meuse rivers. Floods may increase in magnitude and occur more frequently; low discharges are likely to become even smaller and last longer. How to respond to those changes? Can all river functions be fulfilled into the future and which interventions are then needed to keep the country safe and the rivers navigable? The answer to these questions depends on whether climate change is primarily considered as a challenge, or rather as an opportunity to, at the same time, redress a few deficiencies and detrimental geo-ecological developments that are being provoked by how we straightjacketed our floodplains and engineered our rivers in behalf of navigation but negatively impact biodiversity. We propose a more geo-ecologically grounded approach to our rivers’ spatial design and management – inspired by McHarg’s design with nature –, which encompasses making available much more room for safe flood discharge and reduced hydrodynamics for ecosystem development in the floodplains, as well as more nature-based river training to allow for morphological developments and natural rejuvenation. @en

The Netherlands has just finished implementing the Room for the Rivers program along the Rhine and Meuse Rivers in response to increasing river discharges. Recently, making more room for the river is, however, being challenged for future application because the flood defenses are assessed to be too weak and will need reinforcement anyway. To be able to decide on the most desirable policy for the remainder of the century, we require knowledge of all benefits and costs of individual interventions and strategic alternatives for flood mitigation. In this paper, we quantify some benefits of making more room for the rivers. We recognize and quantify two risk-reducing effects and provide results of analyses for the Rhine and Meuse Rivers in The Netherlands. Making room for rivers was originally advocated because it (1) reduces the consequences of flooding, as well as (2) reduces the probability of failure of the embankments. We have now quantified these effects allowing translation into risk reduction proper. Moreover, larger floodplain surface area may influence the relationship between discharge and flood level, which implies that rivers with widened floodplains are less sensitive to uncertainties about future river discharges. This does not reduce risk proper, but makes the river system more robust, as we shall argue in the discussion where we present risk reduction and robustness as complementary perspectives for assessing strategic alternatives for flood risk management@en

There is increasing attention for the robustness of systems, in view of more frequent and more extreme weather events. Calls to increase a system's robustness are usually motivated by the resulting reduced sensitivity to extreme events and uncertainties about their probability of occurrence. The concept has been elaborated for flood risk systems, but recently questions have arisen about whether subsystems, such as flood defences or rivers, should and could also be assessed on their robustness. Against the background of a recent debate in the Netherlands about whether to raise the embankments again or to make more room for the rivers in anticipation of increasing extreme river discharges into the future, we propose to define the robustness of embanked alluvial rivers by their sensitivity to uncertainties in flood discharge, expressed by the relationship between discharge and flood water level. We assess the Rhine River branches and Meuse River in the Netherlands and show how their planform, as defined by the location of the embankments and the presence of obstacles in the floodplains, causes remarkable differences in robustness per river and per river stretch. We finally discuss what this might entail for policy planning.@en