shoreline 



Figure 32. Examples of complete solutions of the distribution of longshore current 



velocities through the surf zone for a series of values for the longshore 

 variation in the wave setup (3n/3y). With 3ii/3y = 0.0025, the setup slope 

 in the longshore direction nearly opposes and balances the thrust due to 

 the oblique wave approach, and the velocities are greatly weakened (from 



of about 8ri/9y = 0.0025 nearly balances the wave-induced thrust so that long- 

 shore currents are greatly diminished. A net circulation flow is possible 

 with nearshore currents in the opposite direction from those near the breaker 

 line. Additional examples are given in Komar (1975a). 



One final application of the decoupled quasi-one-dimensional theory must 

 be mentioned. For the wave-generated current system behind an offshore 

 breaker (Fig. 8), Gourlay (1978) used- principles of radiation stress to 

 develop analytic expressions for the longshore current profiles at various 

 sections. Two basic regions were identified for the analysis. An inflow 

 region of spatially varied flow in the exposed area extended up to the geo- 

 metric shadow of the breaker, and the eddy circulation region within the 

 sheltered area which drains momentum from the primary longshore current sys- 

 tem. Painstaking means were devised to compute the wave breaking heights and 

 locations, wave-induced setup, and to incorporate bottom friction stresses. 

 Lateral mixing stresses were neglected in establishing the velocity distribu- 

 tions. A number of other limitations were imposed in order to derive the 

 final theory. The results, although useful to verify the experiments as dis- 

 cussed in Chapter 4, are not readily generalized to other geometries. Gourlay 

 (19 78) demonstrated the practical limitations for extending a one-dimensional 

 analysis to truly two-dimensional flows. The two coupled momentum balance 

 equations are now needed plus the mass balance equation to solve for the three 

 time-averaged unknowns v, u, and n as described in the next section. 



113 



