SEDIMENT TRANSPORT IN VARIOUS TIME SCALES

Zbigniew Pruszak, Ryszard B. Zeidler

Abstract


Some basic sediment movement characteristics such as critical velocities of motion, bed load layer thickness, as well as local and overall sediment transport have been measured in field at Lubiatowo, Poland. The survey was carried out in a multi-bar (4-5 bars) Polish coastal zone with the medium grain diameter D50 from 0.2 to 0.25 mm. Irydium glass grains tracer, close in size to the natural sand, has been used. The investigations embodied 8 hydrodynamical situations in various climates of waves and currents. For oblique wave incidence it has been found that local intensity of longshore sediment transport can reach 40-100 kg/(m h) under storm conditions, strongly dependent on local bed topography. The overall sediment transport rate across the entire surf zone can exceed 7-10-3 m3/s under storm conditions. For weak wave motion the bed surface layer of sediment transport has a thickness of several grain diameters, while it may be even 4-6 cm thick during storms. Vertical distributions of sediment concentration beneath of bed surface are identified. Transport rates are related to the product of squared breaker height and longshore velocity. Annual time series of sediment transport are presented.

Keywords


time scale; sediment transport

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