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Suspended sediments under plunging waves

Poppe, Mick (2014) Suspended sediments under plunging waves.

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Abstract:Knowledge of the coastal morphology is critical for coastal safety. Unfortunately, knowledge is limited when it comes to sediment transport under irregular breaking waves. In this thesis it is aimed to improve the understanding of suspended sediment concentrations under regular plunging breaking waves. The variation of the sediment concentrations over time and the cross-shore direction is studied, as well as the relation with the water velocities and the net sediment transport. Empirical models are used to describe the concentration profiles of the sediments. Experiments were executed for two months in the CIEM wave flume in Barcelona (Spain). Over a bed development time of 90 minutes a transverse suction system is used to determine the sediment concentrations in the water. Other measuring equipment was used to measure water velocities, bed development and more. Data from especially the transverse suction system is used for analysis. The sediment concentrations decrease from high concentrations in the water at the top of the breaker bar to a less high concentration in the water at approximately 3 meters from the top. Beyond 3 meters from the top of the breaker bar the concentration decreases rapidly and hardly any sediments are found higher in the water column. Over the height the concentrations in general decrease, of course. However, just before and after the breaker bar higher concentrations can be spotted high in the water column, most likely caused by the water velocities and wave actions at these points. The suspended concentrations are also compared to the net sediment transport and show places were sheet flow can occur With empirical models it is possible to fit a function on the suspended sediment data. The parameters of these models show expected trends when looking over the cross-shore position. However, over time there is hardly any trend visible. A timespan of 90 minutes seems not enough to see substantial changes in the development of the models parameters. The thesis gives with figures and clarification a better insight in the concentrations of suspended sediments under regular plunging breakers. However, to get more accurate results, additional research is necessary.
Item Type:Essay (Bachelor)
Faculty:ET: Engineering Technology
Subject:56 civil engineering
Programme:Civil Engineering BSc (56952)
Link to this item:http://purl.utwente.nl/essays/66595
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