MOVABLE BED ROUGHNESS IN THE FLOW OF IRREGULAR WAVES AND CURRENTS OVER MOVABLE BEDS

Zai-Jin You, Peter Nielsen

Abstract


The bed roughness ks in the flow of irregular waves and currents over a movable bed is studied on the basis of measured current profiles and the model of You (1994). It is found that the movable bed roughness kt is affected by both waves and currents and that the existing formulae derived in purely oscillatory flow generally fail to predict ks in the flow of waves and currents. A new formula is proposed to calculate k, in the flow of irregular waves and currents over a movable bed. The present bed roughness formula together with You's (1994) model gives better prediction of current shear velocity u^, and especially apparent roughness z, than the existing formulae derived in purely oscillatory flow.

Keywords


movable bed; bed roughness; bed; irregular waves; current

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