University of Twente Student Theses


Grain size sorting over offshore sandwaves

Wientjes, I.G.M. (2006) Grain size sorting over offshore sandwaves.

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Abstract:Offshore sandwaves are rhytmic patterns on bed of shallow seas. Because of their dimensions and migration rate, they can affect several human activities in these seas. For this reason, morphodynamic models are developed to investigate and simulate sandwave dynamics. The sediment in the sand wave models is up till now assumed to be homogeneous. This means that the sediment consists of grains which all have the same grain size. Natural sediment however, exists of grains with different grain sizes, this is heterogeneous sediment. The transport of heterogeneous sedimens is subject to different mechanisms than the transport of homogeneous sediment and can thus influence the sand wave characteristics. It also may due to the grain size sorting patterns over sand waves, which can be observed in nature. To account for the heterogeneity of the sediment a fractional calculation of the sediment transport is implemented in an existing sandwave model, in combination weith a correction factor that accounts for the fact that grains in heterogeneous sediment do not act as when they are surrounded by grains of the same size. An active layer model preserves sediment continuity. The resulting models shows grains size sorting over sand waves. A coarsening trend towards the crest is found, which agrees with field observations, although the processes seem to be more extreme than in nature. In the sandwave trough the sediment remains mixed.
Item Type:Essay (Master)
Faculty:ET: Engineering Technology
Subject:56 civil engineering
Programme:Civil Engineering and Management MSc (60026)
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