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Title: 1D morphodynamical modelling of swash zone beachface evolution
Author: Zhu, Fangfang
ISNI:       0000 0004 2738 2547
Awarding Body: University of Nottingham
Current Institution: University of Nottingham
Date of Award: 2012
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The beachface evolution in the swash zone under different single swash events is investigated by fully coupled simulations. Two fully coupled models (bed-load-only and combined load models) comprising the one dimensional shallow water equations and bed evolution equation are developed. The two coupled systems are solved by the specified time interval method of characteristics (STI MOC) (Kelly and Dodd, 2009, 2010), which can resolve shocks very accurately. The fully coupled bed-load-only simulations with six different sediment transport formulae for a single Peregrine and Williams (2001) (PW01) swash over an erodible plane beach all yield net erosion all over the swash zone. Consistent with Kelly and Dodd (2010), however, full coupling yields significantly less erosion for all the q=q(u) (q instantaneous sediment flux and u water velocity) formulae compared to the equivalent uncoupled results. It is also shown that including a dependence on h (water depth) in q can result in net deposition in the upper swash, and that with such a formula q the shoreline motion over a plane mobile beach is ballistic in the uprush. Bed shear stress described by the Chezy law is further included in fully coupled simulations, and much reduced maximum inundation and net offshore sediment transport are predicted both for q=q(u) and q=q(h,u). Although the net sediment flux at x=0 under one PW01 event is still offshore, deposition in the middle or upper swash may be predicted when bed shear stress is included. The fully coupled bed-load-only simulation with q=q(u) for a single Hibberd and Peregrine (1979) (HP79) swash event predicts considerable deposition in the swash zone. A backwash bore develops, associated with which a bed step forms when the shoreline catches up with the backwash bore. The subsequent shoreline movement is obtained by the Riemann solution for a wet-dry dam-break problem with a bed step. A bed step also occurs under a solitary wave simulation; its height is much larger than that under the HP79 simulation. Bed step height is found to depend largely on the water depth on the seaward side of the step, which is related to the swash event and the step position. The PW01 and HP79 swash events are also examined by the combined load model. Results show that suspended load results in deposition in the upper swash and erosion in the lower swash. However, pre-suspended sediment results in deposition in the lower swash, implying that net bed change due to suspended load in the lower swash could be depositional. The inclusion of suspended load has much smaller effect on the maximum inundation and swash hydrodynamics than bed load. The inclusion of bed load reduces the maximum inundation significantly; importantly, bed load results in the formation of a bed step and dominates the beach change near the bed step even when suspended load is dominant in the overall beach change.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: TC Hydraulic engineering. Ocean engineering