Figure 4-52. 



Transport directions at New Buffalo Harbor Jetty on 

 Lake Michigan. 



opposite direction. Thus, an erroneous conclusion about the net transport 

 might be made, if only wave patterns of this photo are analyzed. The 

 possibility of seasonal or storm-induced reversals in sediment transport 

 direction should be investigated by periodic inspections or aerial photos of 

 the sand accumulation at groins and jetties. 



The accumulation of sand on the updrift side of a headland is illustrated 

 by the beach north of Point Mugu in Figure 4-53. The tombolo in Figure 4-54 

 was created by deposition behind an offshore barrier (Greyhound Rock, 

 California) . Where a beach is fixed at one end by a structure or natural rock 

 formation, the updrift shore tends to align perpendicular to the direction of 

 dominant wave approach (see Figs. 4-54, and 4-55.) This alignment is less 

 complete along shores with significant rates of longshore transport. 



Sand accumulation at barriers to longshore transport may also be used to 

 identify nodal zones. There are two types of nodal zones: divergent and 

 convergent. A divergent nodal zone is a segment of shore characterized by net 

 longshore transport directed away from both ends of the zone. A convergent 

 nodal zone is a segment of shore characterized by net longshore transport 

 directed into both ends of .the zone. 



Figure 4-55 shows a nodal zone of divergence centered around the fourth 

 groin from the bridge on the south coast of Staten Island, Outer New York 

 Harbor. Central Padre Island, Texas, is thought to be an example of a 

 convergent nodal zone (Watson, 1971). Nodal zones of divergence are more 

 common than nodal zones of convergence, because longshore transport commonly 



4-136 



