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Holocene wave conditions and wave-induced sand transport in the southern North Sea
van der Molen, J.; de Swart, Huibert E. (2001). Holocene wave conditions and wave-induced sand transport in the southern North Sea. Cont. Shelf Res. 21(16-17): 1723-1749. dx.doi.org/10.1016/S0278-4343(01)00018-8
In: Continental Shelf Research. Pergamon Press: Oxford; New York. ISSN 0278-4343, more
Peer reviewed article  

Available in  Authors 
    VLIZ: Open Repository 278834 [ OMA ]

Keywords
    Coasts; Holocene; Modelling; Sediment transport; Wind waves; ANE, North Sea [Marine Regions]; Marine
Author keywords
    wind waves; sediment transport; modelling; coasts; Holocene; North Sea

Authors  Top 
  • van der Molen, J., more
  • de Swart, Huibert E., more

Abstract
    Results are presented of a simple point model of wind-wave conditions (calculated using the JONSWAP wave-growth formulations), wave-induced bottom orbital velocities (linear Airy and Stokes theory) and wave-induced sand-transport magnitudes and directions (Bailard bed-load transport formulation) in the southern North Sea. The main aims of the study are to establish the contribution of wind waves to the instantaneous, and large-scale, open-marine, long-term sand transport, and to determine the dominant transport directions and relative magnitudes. A sensitivity study for the wind climate was carried out, showing a linear response of the net sand transport to the directional distribution of the wind climate, except in a zone of about 100km width along the coasts where the transport pattern is insensitive to such changes. The model is not only applied to the present-day conditions, but also to palaeo situations throughout the Holocene. The palaeo simulations are carried out to demonstrate that the wind wave conditions and associated orbital velocities and sand-transport patterns have changed over time as the basin geometry changed due to the spatially variable relative sea-level rise. The near-bottom orbital velocities are sufficient to initiate sand motion for large parts of the southern North Sea during storm conditions, now and in the past. The sand is transported in this model by the wave asymmetry, the Stokes-drift induced return current and boundary-layer streaming, but the sand stirred up by waves is in reality also available for advection by tidal and residual currents. The present day wind climate was assumed for the palaeo-calculations. The results show that the mean wave heights increased since 7.5kyr BP, the largest changes occurring in the most shallow water, while the mean wave periods remained the same. The wave-induced sand transport mode changed from dominantly suspended transport before 6kyr BP to dominantly bed-load transport thereafter due to the increasing water depth. The overall direction of the bed load transport between 6kyr BP and the present was from east to west, the magnitude decreased slightly. The transports resulted in an erosion zone along the Dutch and Belgian coast, and deposition in the Southern Bight. The interpretation of these results is discussed in the context of other transport factors (tides, wind-driven flow).

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