0.2 -0.4 -0.6 -0.8 -1.0 



Figure 26. Comparison of theoretical longshore current velocity for weak cur- 

 rents, small- and large-angle theories (from Liu and Dalrymple, 1978) 



theories. Although the effort is to be commended, the results are not very ; 

 meaningful since lateral turbulent mixing stresses are neglected in the 

 theories. The reference velocity v* is not a true physical velocity as 

 discussed above. 



Kraus and Sasaki (1979) extended the weak current large- angle theory to ] 

 include lateral mixing stresses. Their contributions are fully examined in j 

 the subsection on lateral mixing. ' 



(3) Strong Currents at Large Angles . For steep (reflective) beaches 

 with narrow surf zones (or smooth bottoms), a bed shear-stress formulation , 

 for both strong currents and large incidence angles is required. Complete ( 

 expressions for Tg and v* (neglecting lateral mixing) are given by Dalrymple I 

 and Liu (1978). The value of v* is questionable. A constant y = H/h ratio ] 

 is used in the surf zone even though plunging-type breakers are normally found | 

 on steep beaches. The theory is of interest for comparison of laboratory ob- I 

 servations but requires modification by lateral mixing and plunging-type 

 breaker formulations in the surf zone. 



96 



