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.

Over the past century, the main channel of the Waal has experienced erosion of approx-imately 1-2 metres (Ylla Arb´os et al., 2021; Chowdhury et al., 2023). This erosion leads to various problems such as instability of struc-tures or disruption to shipping. To address this ongoing degradation, a potential solution is the implementation of sediment nourishments. Recent pilot studies have been conducted in 2016 and 2019 to investigate the feasibility of using sediment nourishments in the main channel of the Dutch Rhine (Becker, 2023). Another possibility of nourishing is to add sed-iment to the groyne fields. Under the influence of currents and ship waves, sediment is ex-pected to be transported to the main channel, causing a groyne field to act as a sand mo-tor. To explore this concept, Rijkswaterstaat initiated a pilot project with sediment nourish-ments in three groyne field clusters along the Waal during the fall of 2023. The pilot includes an extensive measurement campaign.