Author(s): Barbara Boczar-Karakiewicz; Jerry L. Bona; Bernard Pelchat

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Abstract: Multiple longshore sand bars are prominent features in many wavedominated coastal environments.The mechanism of bar formation in nearshoresettings with a gently sloping sea bed(slope S=0.01 and less)has beenexplained by interactions of shallow-water wind-generated waves and swell(Fig.1).The related mathematical model describing this mechanism indicates that thebar morpohologies shown in Figure 1 are strongly correlated with parameters offthe peak-wave of the major storm events characterising the local wave climate(Boczar-Karakiewicz and Davidson-Arnott 1987).In all coastal settings presentedin Figure 1 the major storms are approaching the nearshore from a shore-normaldirection.In the modelling procedure,attention has been focussed on a simpletwo-dimensional description(Boczar-Karakiewicz,Bona and Cohen 1987a).Thistwo-dimensional model also explains the bar stability which was documented byair photography over several decades(Shiels 1986).The observed stabilityconcerns only the linear and shore-parallel outer bars.By contrast,the innerbars are generally sinous and display both,a greater alongshore variability anda faster temporal response to the ambient wave climate(Shiels 1986).Wavemeasurements in the inner nearshore have shown evidence of a significantenergy transfer from the incident,wind generated wave toward oscillations oflower frequencies(Doering and Bowen 1987,Sallenger and Holman 1987,Tatavartiand Huntley 1987).Those low frequency flowB may strongly influence theunderlying bed topography of the inner nearshore.

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Year: 1989