b. Bruun (1963 as Modified) . 



^b = ^2 (^^bf ["'^b (si" 2aj,)/T]'^^ , (4-17) 



where v^ is the mean velocity in the surf zone where the flow is fully 

 developed, and M2 involves a friction factor of the Chezy kind (see 

 Galvin, 1967, p. 297.) 



c. Galvin (1963) . 



vj, = KgmTsin2aj, , (4-18) 



where v^ is the mean velocity in the surf zone where the flow is fully 

 developed, and K is a coefficient depending on breaker height-to-depth 

 ratio and the ratio of trough depression on breaker height. To a good 

 approximation, K may be taken as 1.0. (Galvin and Eagleson, 1965.) 



4.45 SUMMARY 



The major currents in the littoral zone are wave-induced motions 

 superimposed on the wave-induced oscillatory motion of the water. The 

 net motions generally have low velocities, but because they transport 

 whatever sand is set in motion by the wave-induced water motions, they 

 are important in determining littoral transport. 



Evidence indicates that there is only slight exchange of fluid 

 between the offshore and the surf zone. 



Longshore current velocities are most sensitive to changes in breaker 

 angle, and to a lesser degree, to changes in breaker height. However, the 

 volume rate of flow of the longshore current is most sensitive to breaker 

 height, probably proportional to H^. The modified Longuet-Higgins equation 

 (4-16) is recommended for predicting mean longshore current velocity of 

 fully developed flows, and the two semiempirical equations (4-17 and 4-18) 

 are available as checks on the Longuet-Higgins equation. 



4.5 LITTORAL TRANSPORT 



4.51 INTRODUCTION 



4.511 Importance of Littoral Transport . Sediment motions indicated by 

 the shoreline configuration in Figure 4-17 are aspects of littoral trans- 

 port. If the coast is examined on satellite imagery as shown in Figure 

 4-17, only its general characteristics are visible. At this elevation, 

 the shore consists of bright segments that are straight or slightly curved. 

 The brightness is evidence of sand, the most common material along the 

 shore. The straightness often is evidence of sediment transport. 



In places, the straight segments of shoreline cut across preexisting 

 topography. Elsewhere, the shoreline segments are separated by wide la- 

 goons from the irregular mainland. The fact that the shore is nearly 

 straight across both mainland and irregular bays is evidence of headland 



4-50 



