Radiation stress theory has been successfully used to explain the presence of longshore
currents. The original theory is eloquently explained by Longuet-Higgins (1970).
Subsequently Komar (1976), as a result of his own theoretical and field investigations,
developed the theory further and presented revised equations. All of the foregoing is
succinctly summarised in Hardisty (1990). Here a summary of the main principles is
given together with a statement of the main equations.