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Abstract: Experimental program was conducted to analyze scour – caused by a horizontal jet downstream of a rigid bed – and the flow velocity and turbulence characteristics within the scour hole. The experimental program was motivated by the fact that the knowledge of flow field, including turbulent characteristics, is fundamental to correctly simulate the bed-load transport and the temporal evolution of the scour hole and, thus, to define protective measures of scouring. In this paper some results of experiments – carried out to understand the role of flow turbulence in the prediction of scouring process and sediment movement – are reported. The analysis is conducted on the basis of detailed measurements of flow velocity at various sections in the scour hole region. Both a 2D LDA anemometer and an acoustic velocimeter profiler (DOP2000) were used to conduct the velocity measurements. The results show that the flow is characterized by alternating high-low speed fluid regions which lead to the formation of vertical turbulent coherent structures. The turbulent intensity assumes significant values along longitudinal planes (i.e. parallel to the flow direction) in the near-bank zones. Maps documenting the correlations between the vertical and the longitudinal turbulent intensities are shown. With the aid of the experimental data, a relationship between the bed shear stress and the volume of sand eroded is defined. The quadrant analysis is applied for the qualitative description of the turbulent events. Analysis indicates that the major turbulent activity occurs in the deepest region of the scour hole. It seems that sweep and ejection events, which correspond to positive production of the turbulent energy, play an important role in erosion and transport of the sediment particles. [Copyright &y& Elsevier]

Abstract: The hydrologic regime of the Tiber River basin in central Italy has been impacted considerably in the last decades by intensive anthropic activities, and hydraulic works in particular (e.g. hydropower reservoirs, land use modification). In the Tiber River the wash load, in particular, plays an important role in sediment transport, and the knowledge of this hydrological variable is very important for the evaluation of medium–long-term dynamic of shoreline, and the evaluation of reservoir landfill. The Ripetta flow gauge, located in downtown Rome, has been continuously monitoring the daily discharge for decades, while daily sediment load measurements are available only for short terms. In this research, the yearly sediment rate is simulated using a simple stochastic model based on the evaluation of sediment rating curves. The sediment rating curve, i.e. the average relation between discharge and suspended sediment concentration for a specific location, is estimated using a power law model. The fitting curve, obtained by regression analysis, lacks the physical characterization of the phenomenon, often represented by the empirical evidences of erosion severity and the erosional power of river. Model results provide useful insights on the impact of recent hydraulic works on the sediment transport regime. [Copyright &y& Elsevier]

Abstract: Numerous models for predicting sediment transport rates have been developed over time. Nevertheless, the predictive accuracy of these models is often questionable. The transport mechanism is complex, and the deterministic transport models are based on simplifying assumptions that often lead to large prediction errors. Data-driven modelling can be useful for modelling processes about which adequate knowledge of the physics is limited. In the present paper a sediment transport model based on an artificial neural network (ANN) is presented. The predictive accuracy of the ANN model on the data sets compiled by Brownlie was found to be better than that of Engelund-Hansen and Van Rijn. A conclusion is reached that the data-driven modelling approach is suitable for modelling sediment transport. [Copyright &y& Elsevier]

A concept for the continuous modelling of erosion, solute and sediment transport at the catchment scale is presented. The simulation is based on the application of the OPUS model designed for single slopes. In order to apply the model at the catchment scale, the study area (54 km2) is discretized into numerous slopes. The simulation results are compared with measurements at different spatial and temporal scales of a mesoscale catchment used for drinking water supply. Three small sub-catchments, ranging between 21 and 29 ha, are used to validate the model at the local scale. Process observations at this scale are used to modify the OPUS model. While for the validation of the long-term water and solute transport daily measurements at the catchment outlet were available and used, the long-term simulation of the sediment transport is validated by analysing the sediments trapped in the drinking water reservoir.The results suggest that the model concept is applicable to a large range of scales from single events to decades and from single slopes to mesoscale catchments. However, the quality of the simulation depends on the kind of process considered. Best model results are achieved with the simulation of runoff and nitrate discharge, whereas the simulation of sediment transport is less satisfying. [Copyright &y& Elsevier]