Interaction of swash and sediment on the backshore in the presence and absence of barriers
Thesis/Dissertation
·
OSTI ID:5413567
A laboratory flume experiment was conducted to investigate the interaction of uprush and backwash and sediment transport 1) under normal maximum run-up conditions, 2) in the presence of a vertical impercious wall, 3) in the presence of an inclined sand dune face, 4) in the presence of a vertical sand dune scarp and 5) overtopping of a beach crest with flow away from the wave source. Water was introduced at the base of the laboratory beach as a bore and gave uniform run-up for all the experiments. Depth of uprush and backwash flow was measured with three to four capacitance water level gauges while velocity was measured by electromagnetic current meters. Sediment bed changes were measured before and after each surge. The normal backwash after maximum run-up consisted of a thinning water mass of accelerating unidirectional flow. The calculated backwash discharge gradually increased to a maximum just before the end of backwash. As the run-up collides with the vertical wall a plunging type breaker form is created that collapses to form a reflected bore that travels downslope over the thinning backwash. Turbulence associated with the collision causes scour at the base of the wall. Field studies confirm the scour at the base of a vertical wall. Barriers to swash run-up enhance the scour of the backwash through development of a reflected bore. The undercutting of vertical sand walls serves as a source for sediment to the foreshore. Swash that overtops a beach crest carries most of the sediment landward. The reduced volume of backwash transports little sediment.
- Research Organization:
- Virginia Univ., Charlottesville (USA)
- OSTI ID:
- 5413567
- Country of Publication:
- United States
- Language:
- English
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