Longshore Currents in Two Laboratory Studies: Relevance to Theory

Abstract

Most post‐1970 theoretical studies of longshore current velocity extend the radiation stress theory of Longuet‐Higgins. Of the two larger sets of laboratory data (1949, 1963) available to test theories, Longuet‐Higgins used the 1963 data and considered but did not use the 1949 data. Most post‐1970 theories reverse these judgments and rely on the 1949 data. Such theories must be reevaluated. The 1949 data are 37 experiments, of which 22 were run on slopes steeper than all but the steepest natural foreshores; 12 of 37 published breaker angles exceed the generator angle; breaker depth‐to‐height ratios for the steep laboratory slopes were computed (not measured) using empirical curves from flat field slopes; and dimensionless velocities have a unique distribution. Breaker angle is the most sensitive variable determining longshore current velocity. Properly defined breaker angles require duplicate measurements along the test beach. The test velocity selected to compare with theory must account for the nonunifo...