R reflective wave front 



R Reynolds number (=UL/v ) 



R time- averaged, lateral Reynolds number 



r constant from Longuet-Higgins (1970) 



(=7i6Pq '^Y (tan B) '^ ( — ^ — )) 



r bottom roughness 



S.. components of the radiation stress tensor 



S..^ components of the fictitious radiation stress tensor without 



breaking 



S time-averaged value of the total flux of horizontal momentum 



across a vertical plane minus the Stillwater hydrostatic 

 pressure force 



S principal wave thrust (radiation stress) perpendicular 



to the wave crest 



S the shear-stress component due to the excess momentum flux. 



xy 



The shear stress is exerted in the y-direction on a fluid 



surface constant in x 



S ^ component wave thrust parallel to shoreline 



S principal wave thrust (radiation stress) parallel to wave 



crest 



S the shear- stress component due to the excess momentum flux, 



yx 



The shear stress is exerted in the x-direction on a fluid 



surface constant in y 



S-. =S transformed wave thrust component in x-direction 



S„„=S transformed wave thrust component in y-direction 



S^„=S„ =S transformed shear-stress component 



T wave period 



T deepwater wave period 



T lateral shear force 



tan 6* slope of MWL due to wave setup 



U Ursell number 



16 



