EFFECTS OF A BREAKWATER ON NEAR-SHORE CURRENTS DUE TO BREAKING WAVES.

THE OBJECTIVE OF THIS STUDY IS TO PROVIDE A SEMI-EMPIRICAL THEORY OF NEARSHORE CURRENTS DUE TO BREAKING WAVES IN THE PRESENCE OF (I) A SHORE-CONNECTED BREAKWATER OR (II) AN OFFSHORE BREAKWATER.IN PARTICULAR, THE EFFECTS OF DIFFRACTION ARE STUDIED IN ADDITION TO REFRACTION BY SHOALING WATERS.THE CONCEPT OF RADIATION STRESSES RECENTLY APPLIED TO UNIFORM LONGSHORE CURRENT AND RIP CURRENTS FORMS THE STARTING POINT OF THE THEORY HERE.MANY EMPIRICAL RELATIONS INVOKED HEREIN WITH REGARD TO THE SURF ZONE ARE SIMILAR TO, AND EXTRAPOLATIONS OF, THE ONES USED IN RELATED RECENT WORKS.IGNORING CONVECTIVE INERTIA AND LATERAL TURBULENT DIFFUSION THE GOVERNING EQUATIONS ARE SOLVED NUMERICALLY BY THE METHOD OF FINITE DIFFERENCES.SAMPLE RESULTS FOR STREAM FUNCTIONS AND MEAN SEA LEVELS ARE PLOTTED FOR VARIOUS BEACH PROFILES OR INCIDENCE ANGLES.FOR THE OFFSHORE BREAKWATER THE PREDICTED CURRENT PATTERN IS CONSISTENT WITH AVAILABLE LABORATORY OBSERVATIONS AND THE KNOWN TENDENCY OF TOMBOLO FORMATION.FOR THE SHORE-CONNECTED BREAKWATER, THE COMPUTED FLOW PATTERN EXHIBITS CELLS IN BOTH DOWN-WAVE AND UP-WAVE REGIONS.DIRECTLY RELEVANT OBSERVATIONS HAVE NOT BEEN FOUND BUT PART OF THE PREDICTED FEATURES HAS SOME INDIRECT EXPERIMENTAL SUPPORT.MORE EXPERIMENTAL AND THEORETICAL WORK IS SUGGESTED.(A.)