Wave-generated currents

Gourlay, M. R. (Michael Richard) (1978). Wave-generated currents PhD Thesis, School of Engineering, The University of Queensland.

       
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Author Gourlay, M. R. (Michael Richard)
Thesis Title Wave-generated currents
School, Centre or Institute School of Engineering
Institution The University of Queensland
Publication date 1978
Thesis type PhD Thesis
Supervisor Professor G,R, McKay
Total pages 2v
Language eng
Subjects 260400 Oceanography
Formatted abstract A comprehensive investigation and review of literature has been made concerning the nature and characteristics of the wave-generated currents which cause alongshore sediment transport (littoral drift).

An historical summary of early research up to about 1969 revealed many of the qualitative characteristics of wave-generated currents and associated nearshore circulation systems, but also showed that no consistent theoretical basis nor any adequate empirical data were then available for the quantitative prediction of current velocities. The "radiation stress" theory of Longuet-Higgins and Stewart now provides a unified theory for wave-generated currents and associated phenomena such as wave set-up. A comprehensive review of this theory is presented, together with its application both to the computation of uniform alongshore currents and to mathematical models of nearshore circulation systems.

The author has made an experimental laboratory investigation of an idealized nonuniform alongshore current system generated on a beach behind an offshore breakwater. In this study the beach plan form was arranged so that the breaking wave crests were parallel to the beach at all times, and the resulting alongshore current was driven by the alongshore gradient of wave set-up created by the alongshore gradient of the breaking wave height resulting from diffraction behind the offshore breakwater. The results of experiments with various wave heights and periods show that the wave height is the dominant factor in determining the resultant alongshore current, and that the wave period is of secondary importance only. Wave-current interaction effects are significant.

The assumption of shallow water conditions has enabled the author to derive simple formulae for computing the wave set-up of both plunging and spilling breakers on both steep and flat beaches. These formulae are used in conjunction with the momentum principle including radiation stress terms to obtain an expression for computing the velocity of the nonuniform alongshore current.

Further analysis permits the velocity distribution to be computed neglecting lateral mixing effects. Bottom friction is allowed for using the nonlinear expressions of either Jonsson, Skovgaard and Jacobsen or Bijker and Swart. These expressions are also applied to uniform alongshore current data from various sources and the results compared with those obtained using linearized theory. The author's expressions for computing the velocity of a nonuniform alongshore current are applied to three actual situations.

Finally the influence of wave-generated currents on the alongshore sediment transport in the vicinity of engineering structures and/or natural coastal features is considered for a number of specific cases. Some of the general principles involved in the development of the alignment and morphology of sedimentary coasts are outlined, together with a discussion of rip current systems and their interaction with beach and bottom topography.

Keyword Ocean currents
Sediment transport

 
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