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This paper shares an early-career perspective on potential themes for the upcoming International Association of Hydrological Sciences (IAHS) Scientific Decade (SD). This opinion paper synthesizes six discussion sessions in western Europe identifying three themes that all offer a different perspective on the hydrological threats the world faces and could serve to direct the broader hydrological community: "Tipping points and thresholds in hydrology," "Intensification of the water cycle," and "Water services under pressure." Additionally, four trends were distinguished concerning the way in which hydrological research is conducted: big data, bridging science and practice, open science, and inter- and multidisciplinarity. These themes and trends will provide valuable input for future discussions on the theme for the next IAHS SD. We encourage other early-career scientists to voice their opinion by organizing their own discussion sessions and commenting on this paper to make this initiative grow from a regional initiative to a global movement. [ABSTRACT FROM AUTHOR]

Mobile components of dynamic river systems are varied, and more than fundamental water and sediment interactions must be considered to assess morphodynamic changes. Here, the effects of instream wood and plastic accumulations on the riverbed are modelled and assessed in the presence of a hydraulic structure. We observe a recent tendency towards considering instream wood and plastics as integral riverine system components. Such shift is driven by a multidisciplinary interest in instream wood and riverine plastic dynamics, including those addressing flood hazards and risk assessments. Like sediment, instream wood and plastics can be transported along the river channels during floods, increasing flooding risks and hazards by accumulating near hydraulic structures. Collection racks, a commonly encountered hydraulic structure, are used for trapping and removing various accumulated material, mitigating any potential risks. However, accumulations at collection racks can cause other risks because of potential backwater rise and local scour development. Accumulations of different densities, such as a combined presence of instream wood and plastics, add further complexity to the process understanding. In this study, a physical model is used to explore the geomorphic effects of accumulations of two different densities at a collection rack. Local geomorphic changes (i.e., scour and deposition), their evolution and the spatial extent around a vertical collection rack were analysed with Structure from Motion photogrammetry. The results show a strong relationship between the accumulation density and the hydraulic and geomorphic changes. Light floating material, forming accumulations closer to the water surface, are associated with the largest geomorphic changes, in contrast to dense material, forming accumulations close to the riverbed. In the presence of different densities, intermediate geomorphic changes were observed. Finally, to discuss the observations, we present a conceptual flow field for different scenarios of accumulation densities. Ultimately, outcomes from this work are essential to improve design practices for river managers. [Display omitted] • Plastic and wooden dowels were used to model materials of different density. • Light material accumulations result in the largest geomorphic changes. • Dense material accumulations result in the least geomorphic changes. • Accumulations of mixed density result in intermediate geomorphic changes. • Maximum backwater rise occurred at the beginning of the accumulation's formation. [ABSTRACT FROM AUTHOR]