beach at an angle. Table 2 (modified from Ostendorf and Madsen, 1979) lists 

 the idealized environment along with those stresses and accelerations that 

 have been neglected. This list is long but many of these restrictions have 

 been relaxed in later generalizations of the basic theory, which will be re- 

 viewed separately, mostly in Sections V and VI. In addition, the basic theory 

 for uniform longshore current profile has undergone considerable modification 

 from the original models first introduced about 1970. These modifications 

 primarily reflect the influences of wave incidence angle, bottom shear stress, 

 and lateral turbulent mixing approximations and assumptions in the surf zone. 

 The original models and all subsequent modified theories for uniform longshore 

 current profile are reviewed in this section. 



Table 2. Idealized environment for longshore current theory. 



WAVE FIELD 



Simple, monochromatic gravity wave trains 

 Steady-state, incident wave field 

 Two-dimensional, horizontally propagating 

 Linearized theory and radiation stresses 

 Oblique angle of incidence, long wave crests 

 Spilling-type breakers 

 Constant breaker ratio in surf zone 



BEACH 



Infinite length, straight and parallel contours 

 Plane bottom slope 

 Gentle slope 

 Impermeable bottom 



FLUID 



Incompressible 



Homogeneous (no air entrainment) 



CURRENT 



Depth- integrated, parallel to coastline 

 Time-average (one wave period) 



NEGLECTED STRESSES AND ACCELERATIONS 

 No surface wind stress 

 No atmospheric pressure gradient 

 No Coriolis acceleration 

 No tides 



No local (time-average acceleration, i.e., steady flow 

 No wave- turbulence interaction stresses 

 No bed shear stress outside the surf zone 

 No rip currents present 

 No wave-current interaction stresses 



79 



