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<p>Sediment transport in rivers consists, at a moderate discharge stage, of individual grains that undergo a series of step movements and rest periods (bedload). In this study, we exploited available data representing resting time and jump length of particles involved in bedload processes. Following the entropy approach based on Shannon and Tsallis theories, we got formal probability functions describing the distribution of the above-mentioned kinematic quantities. Finally, accepting the Einstein assumptions and exploiting the experimental data, we found the values of the constants involved in the entropy functions and complete the analysis. A comparison between experimental and theoretical distributions is showing encouraging matches.</p><p>An indirect, but quite relevant, way to prove the validity of the obtained probability distribution, is worked out by looking at the dispersion of traced grains, originally located in well-bordered pillows at different depths within the bed. The application of a stochastic model able to move the grains of the bed with prescribed frequencies in space and time allowed us to further appraise a good behavior of the entropy-based distributions versus the experimental ones.  </p><p>Future directions of this research would address the important goal nested in the detection of river flow with or without bedload, by using entropy information based on the measurement of velocity field and/or flow depths over cross-sections.</p>

The present work concerns the interaction between hydraulic processes and biological communities in rivers. In particular, the aim of this study is to investigate the interactions between flow dynamics and the freshwater mussels (FMs) to verify if the mussels' behavioural response to the hydrodynamic stress could be used to monitor natural extreme events in rivers. Although the influence of mussels on the kinematic characteristics of flow at the water–sediment interface was investigated by a certain number of studies, their behavioural response to flow, both in static and dynamic conditions, remains understudied. Laboratory experiments were performed in an artificial flume exposing Unio elongatulus to different values of flow discharge, both in steady and in unsteady conditions either with or without sediment transport. Mussels' behavioural responses were detected by using Hall sensor technology to measure gaping frequency, amplitude and duration, both in static conditions and under the effect of hydrodynamic stresses. Five categories of behavioural response were identified: Normal Activity (NA), Resting (Re), Transition (Tr), Adaptation (Ad) and Avoidance (Av). During NA (standard feeding and moving), FMs presented valve gaping, while during Re valves were kept constantly opened for water filtration. After a variation of flow discharge (ΔQ), FMs promptly reacted showing a transition from their normal behaviour, with constant gaping frequency (below 0.01 Hz), to higher valve gaping frequencies. The mean valves' gaping frequency increased as a function of ΔQ, and the highest values were reached in the presence of sediment transport. The mean valve opening amplitude was less sensitive to ΔQ. Its range of variation was very narrow with the highest values corresponding to the protrusion/retraction of the animals' foot to move or anchor to the substrate. The percentage of mussels responding to the discharge variation (Transition behaviour) increases with ΔQ confirming that mussels' behavioural response represents a promising tool for monitoring the occurrence of hydrodynamic stressors in fluvial systems.

The effect of the elliptic ratio on the hydraulic performance of the LOPAC gate has been investigated using experimental and Computational Fluid Dynamics $$CFD$$ CFD simulations (Flow-$$3D$$ 3 D Hydro). Experiments and simulations were carried out at three different flow discharges, three different submerged ratios, and five different elliptic ratios. In this context, the $$CFD$$ CFD model was first calibrated and verified using the measured data, and then $$CFD$$ CFD simulation was performed. The ratio of upstream/downstream flow depth, the flow discharge coefficient, and the energy dissipation through the gate have been calculated and analyzed, and the three-dimensional features of the flow have been described. Based on the results, the elliptical LOPAC gates with circular weirs determine extreme values of the controlled flow parameters. Asymmetric recirculation downstream of the gate is sometimes observed in the model predictions. The use of Coriolis coefficients relevant to the entire cross-section, here deployed just for the circular and the traditional rectangular Lopac gates, has allowed a concise way to report and compare complex flows for any experimental condition.