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. 



Figure 4-53. 



(4 December 1967) 

 Transport Directions at New Buffalo Harbor Jetty on 

 Lake Michigan 



The accumulation of sand on the updrift side of a headland is illus- 

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

 Figure 4-55 was created by deposition behind an offshore barrier (Grey- 

 hound Rock, California). Where a beach is fixed at one end by a struc- 

 ture or natural rock formation, the updrift shore tends to align perpen- 

 dicular to the direction of dominant wave approach. (See Figures 4-55, 

 and 4-56.) This alignment is less complete along shores with signifi- 

 cant 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: diver- 

 gent and convergent. A divergent nodal zone is a segment of shore char- 

 acterized 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 4-56 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 



4-142 



