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The management tools for understanding and preventing flood risk are generally developed from knowledge pertaining to the fields of hydrology and hydraulics. Hazard mapping is mainly based on hydraulic modeling, while the analysis of the flood risk trajectory considers the effect of climate change, spatial planning and socioeconomic policies on the hydrological regime. In the vast majority of cases, the analysis of the flood hazard is based on the link between hydrology and hydraulics, leading to an incomplete representation of the phenomenon. The flood hazard depends on the evolution of the hydrological regime, but also on changes in the geometry and hydraulic capacity of the channels that are related to the hydrological and sedimentary regimes of the drainage basin. Integrating concepts and knowledge from hydrogeomorphology can contribute to the emergence of a more holistic vision of flooding phenomena. At a time when flood risk management must increasingly be considered in a cross-disciplinary way, hydrogeomorphology tools and concepts can enhance the work of any manager or professional in the field of flood risk.

Turbulence organizes river flows and contributes to fluvial dynamics. Key methodologies and classical measures that are used to document the structure of turbulent flows and the presence of coherent flow structures are presented. The progress made in characterizing the nature of turbulent flows in rivers has led to a better understanding of the origin of coherent flow structures. Selected examples are presented to describe how river morphology promotes the formation of coherent flow structures in rivers as well as to illustrate the structure of turbulent flows. River flows encompass a plethora of coherent flow structures that interact with each other. This creates a general structure to the flow that can be described and used to understand the role of turbulence in fluvial dynamics.

Flow refugia provide a mechanism that can explain the persistence of macroinvertebrate communities in flood-prone, gravel-bed rivers. The movement behaviour of macroinvertebrates is a key element of the flow refugia hypothesis, but surprisingly little is known about it. In particular, little is known about how local near-bed hydraulics and bed micro-topography affect macroinvertebrate movements. We used a novel casting technique to reproduce a natural gravel-bed substrate in a large flume where we were able to observe the movement behaviour of the cased caddisfly, Potamophylax latipennis at different discharges. The crawling paths and drift events of animals were analysed from video recordings and used to classify sites on the substrate according to the type of insect movement. We used acoustic Doppler velocimeter (ADV) measurements close to the boundary to characterise hydraulic conditions at different sites and a detailed Digital Elevation Model (DEM) to characterise sites topographically. Animals made shorter more disjointed crawling journeys as discharge increased, although they tended to follow consistent paths across the substrate. As hypothesised, crawling behaviour was locally associated with low elevations, low flow velocities and low turbulent kinetic energies, while sites that insects avoided were characterised by higher elevations, velocities and turbulence. Discrimination was greater at higher discharges, indicating that movement behaviour is contingent upon flow conditions. We suppose that these relations reflect the need of animals to reduce the risk of entrainment and minimise energy expenditure by avoiding areas of high fluid drag. As discharge increased, there was a general upward shift in the frequency distributions of local velocities and turbulent kinetic energies. The animals responded to these shifts and it is clear that their different activities were not limited to fixed ranges of velocity and turbulence. We assume that the absolute hydraulic forces would become a limiting factor at some higher discharge. At the discharges examined here, which are below those required to instigate framework particle entrainment, patterns of animal movement appear to be associated with the animals’ experiences of relative rather than absolute hydraulic forces.