A cross-shore transport "shape function'" for high energy beaches

Field measurements of cross-share velocities were obtained, using electroma gnetic current meters, from morphodynamically reflective, intermediate and dissipative macrotidal beach sites, during high energy conditions. The domi nant velocity moments outside the surf zone were found to predict (1) onsho re transport associated with the short wave skewness, (2) onshore transport associated with short wave stirring, and transport by a weak mean onshore flow, and (3) offshore transport due to short wave stirring in long wave tr oughs. Inside the surf zone the dominant velocity moments predicted (1) off shore transport caused by both short and long wave stirring and subsequent offshore transport by the undertow, (2) weak onshore transport associated w ith the short wave skewness, and (3) at the dissipative site, offshore tran sport associated with the long wave skewness. By plotting the normalised velocity moments for all the field sites against normalised depth, a second order polynomial 'shape function' was produced for the total velocity moment, which predicts onshore transport seaward of the surf zone decreasing in magnitude towards the breakpoint, and offshore transport inside the surf zone increasing in magnitude towards the shorelin e. It is suggested that this shape function represents a quasi-universal cr oss-shore sediment transport spatial distribution curve for high energy bea ches.