The upper Dutch Rhine branches show continuous bed degradation (1-2 cm/year) threatening multiple river functions. The bed degradation is a response to past sand mining, channel narrowing and straightening, which increased sediment transport capacity and created a sediment transport gradient that drives ongoing erosion (Figure 1). Room for the River 2.0 (RftR 2.0) aims to create a climateresilient river system, supporting river functions. Arresting bed degradation is essential to prevent further deterioration of river functions. For the Waal River, two principal intervention strategies were investigated: (1) continuous sediment management and (2) a large-scale implementation of the multi-channel approach. While sediment nourishment counteracts ongoing erosion by supplying the deficit in the sediment balance, the multi-channel approach reduces sediment transport by diverting discharge from the main channel to a parallel side channel. The objective of this abstract is to determine the effectiveness of both interventions in arresting bed degradation. We present the results of the intervention strategies evaluated with a quasi-3D morphodynamic model (Delft3D) in which the multi-channel approach is schematised as longitudinal training walls separating a side channel from the main channel. ... Read more

The last decades have shown an increase in the frequency and magnitude of floods (Blöschl et al. 2020). The intensification of flood regimes will likely enhance rivers’ capacity to erode and transport sediment. Sedimentary properties, such as texture, porosity and geochemistry are crucial factors that affect the economic and ecologic values of overbank zones. Moreover, understanding of sediment fluxes and pathways is also key in predicting the distribution of adhesive heavy metal contaminants, microplastics and forever PFAS chemicals. Yet, modelled estimates of sediment transport and overbank deposition are notoriously inaccurate. A recent experimental study of bed load transport suggested up to a factor 5 attributable to the shape of particles (Deal et al., 2023). Here we show that the shape of sand grains is probably also a critically overlooked factor in suspended sediment transport. Its effects are observed from lateral-distance sorting in overbank deposits from different catchments. We used hydraulic modelling to further test our initial observations and to explore the magnitude of changes in sediment transport that are potentially caused by grain shape. ... Read more

Groynes are commonly found in lowland rivers, where they help maintain a navigable main channel depth and prevent bank erosion. The areas between them, the groyne fields, mainly consist of sediments. The morphodynamics of groyne fields have been studied through laboratory experiments (Yossef & De Vriend, 2010) and numerical models (McCoy et al., 2008; Constantinescu et al., 2009). However, these controlled experiments do not capture the spatial variability observed in natural settings. Based on field measurements Ten Brinke et al. (2004) hypothesized that groyne fields gradually erode under the influence of shipping, while substantial sedimentation occurs during floods. Our objective is to provide a more thorough understanding of the natural variability in groyne field bed level changes with the ultimate purpose to assess the potential and efficacy of groyne field nourishments. To this end, we first establish a baseline representing the natural variability in groyne field bed level changes. Additionally, understanding the factors that govern this baseline is essential. ... Read more

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. ... Read more

Wave overtopping is commonly measured using overtopping tanks. In this paper, an alternative system is developed by using two laser scanners. It measures wave run-up, as well as layer thicknesses and front velocities, both during normally and obliquely incident waves on a dike in the field. The paper considers the first field validation tests with the system, with normal and oblique waves generated by the wave run-up simulator on a grass dike slope. Furthermore, a range of environmental conditions are simulated, to determine the robustness of the system. From the measured distance and reflection, the run-up is determined, which corresponds well to the observed run-up. From the data, the layer thickness and front velocity are determined as well. Layer thicknesses and front velocities are determined reliably with the laser scanners. Also, the (virtual) wave overtopping discharge can be calculated, which corresponds well with the most commonly used overtopping equations. ... Read more