IV-142 



maintenance to maintain access and berthing space. This may take 

 the form of a channel six feet deep or one forty deep, depending 

 upon the ship traffic. Table IV. 2. 9 shows the amount of dredging 

 required by the Corps of Engineers to maintain the harbors of 

 United States Ports. 



Jetties are a less common item on the coastal scene. These structures 

 are generally placed where it is necessary to protect a channel and 

 are usually built only where narrow harbor entrances are subjected to 

 shoaling and wave action. On the west coast of the United States jet- 

 ties are often used to form harbor enclosures as in Los Angeles Harbor 

 and Halfmoon Bay (Figure IV. 2. 25). 



Groins are not too frequently used in the estuarine environment. Nor- 

 mally they are built along sandy coastal beaches to help control beach 

 erosion. The groins effectively interfere with the littoral transport 

 phenomena by trapping materials that would be carried away; they are 

 used extensively along the east coast and in southern California. 



Utilizing barriers to protect the land from the fury of storms at sea 

 is a procedure that has been frequently proposed but little used. 

 There are two examples of hurricane barriers along the east coast, in 

 New Bedford, Mass., and Providence, R.I. Schemes have been developed 

 for other hurricane barriers in Narragansett Bay and Tampa Bay but 

 have not materialized. Feasibility investigations of a tsunami 



