Growth of longshore currents downstream of a surf-zone barrier

Momentum flux considerations are used to formulate a differential equation governing the growth, with distance, of the mean longshore current velocity in the surf-zone on a plane, impermeable beach due to monochromatic waves. The equation is solved for the flow situation downstream of a surf-zone barrier and is shown to compare favorably with laboratory measurements. The asymptotic (uniform flow) form of the relation is also shown to be in good agreement with the field and laboratory data of other investigators. Conclusions are reached governing the size of laboratory models necessary to represent conditions of fully developed longshore currents

Experimental study of longshore currents on a plane beach

Measurements are made of the characteristics of breaking waves and the resulting longshore currents for 34 combinations of wave height (up to 0.22 feet), period (0.90 to 1.50 seconds), and breaker angle (up to 320), along a 20 foot test section of a 30 foot plane, smooth concrete beach with a 0.104 slope. Techniques are developed to measure the distribution of longshore current velocity and of mean water level in the surf zone, and the measurement of breaker point and angle for plunging waves on a laboratory beach is standardized. The nature of the growth of the longshore current in the lee of an impermeable obstacle is studied. In addition to the expected increase of the current velocity downstream of such an obstacle the mean water level is found to increase and the breaker position and runup limit to move shoreward. It is not clear to what extent these latter effects are influenced by the scale of the apparatus used