Sediment yield and transport: estimation and climate influence

Erosion, transfer and deposition of soil particles due to water and the impact of climate change on these physical processes have acquired a great importance during the last decades.Indeed, it is the subject of focused research in several fields of the earth sciences (such as hydrology, hydraulics, ecology, agriculture, geology, civil and environmental engineering, etc.), as the result of the continuous increase in hydrogeological risk in different geographical areas around the world, including Italy.Knowledge of the sediment volumes generated and transported by streams is useful, for example, for the successful design of hydraulic infrastructures, dams or reservoirs, for changes to forest waterways and terrain, for the land management and environment, etc. Sediment production at the catchment scale and solid transport in rivers can be assessed and quantified through mathematical and empirical models.Unfortunately, there is a shortage of gauged data regarding sediment fluxes and production at the catchment scale, because of topographical and pedological complexity and high spatial variability of all the hydrological characteristics.Another point that should be taken into account is the scarce availability of the appropriate equipment to make survey measurements.For these reasons, it is hard to implement monitoring techniques.However, in the absence of field data, major elements for land management, planning and protection include an estimate of soil loss and sediment yield and their comparison with other case studies.In the first part of this thesis project, a detailed sediment transport analysis in a reach of the Mimico Creek, which is located in Southern Ontario (Canada), was conducted by making use of the sediment transport investigations.A hydraulic model was developed and calibrated through the HEC-RAS software, by using the Wilcock and Crowe transport function, to a series of discharge events where in-situ bedload sampling occurred.Bedload samplings used in calibrating the transport model were limited by the orifice of the Helley-Smith bedload sampler (ranging between 0.5 mm and 32 mm).Calibration curves, that determine bed material transport rates as a function of the dimensionless reference shear stress, were created considering both step-wise discharge and unsteady flow simulations.The results of the calibrated model were used to calculate the mean travel distance of bed material: the goal was to compare the simulation results achieved to field observations, derived through the bed material particle tracking (RFID technique).The values achieved showed that the Wilcock and Crowe equation under-predicts the transport of the coarsest fractions in the bed load and that the travel distances calculated considering the BSTEM option (which also considers the presence of fine material from bank erosion) are longer.Finally, the travel distances of different grain sizes were estimated using the calibrated model results.The obtained values showed that particles have a steep reduction in travel distance with an increase in their size.Furthermore, transport distance values are higher for the flood events with higher peak discharges, generally in accordance with field measurements.The fractional transport distances of different grain classes estimated by using simulation results are lower than tracer surveys because in the field only the mobile particles were considered, Sediment yield and transport: estimation and climate influence

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