Experimental study of longshore currents on a plane beach

Abstract

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.