1.54 BULKHEADS, SEAWALLS AND REVETMENTS 



Protection on the upper part of the beach which fronts backshore 

 development is required as a partial substitute for the natural pro- 

 tection that is lost when the dunes are destroyed. Shorefront owners 

 have resorted to shore armoring by wave- resist ant walls of various 

 types. A vertical wall in this location is known as a bulkhead, and 

 serves as a secondary line of defense in major storms. Bulkheads are 

 constructed of steel, timber, or concrete piling. For ocean-exposed 

 locations, bulkheads do not provide a long-term solution, because a 

 more substantial wall is required as the beach continues to recede and 

 larger waves reach the structure. Unless combined with other types of 

 protection, the bulkhead must be enlarged into a massive seawall capable 

 of withstanding the direct onslaught of the waves. Seawalls may have 

 vertical, curved or stepped faces. While seawalls may protect the up- 

 land, they can create a local problem. Downward forces of water created 

 by waves striking the wall, can rapidly remove sand from in front of the 

 wall. A stone apron is often necessary to prevent excessive scouring 

 and undermining. 



A revetment armors the slope face of a dune or bluff. It is usually 



composed of one or more layers of stone or is of concrete construction. 



This sloping protection dissipates wave energy with less damaging effect 



on the beach than waves striking vertical walls. 



1.55 BREAKWATERS 



Beaches and bluffs or dunes can be protected by an offshore break- 

 water that reduces the wave energy reaching the shore. However, offshore 

 breakwaters are usually more costly than onshore structures, and are sel- 

 dom built solely for shore protection. Offshore breakwaters are construc- 

 ted mainly for navigation purposes. A breakwater protecting a harbor 

 area provides shelter for boats. Breakwaters have both beneficial and 

 detrimental effects on the shore. All breakwaters reduce or eliminate 

 wave action and thus protect the shore immediately behind them. Whether 

 offshore or shore-connected, the elimination of wave action reduces long- 

 shore transport, obstructing the movement of sand along the shore and 

 starving the downdrift beaches. 



At a harbor breakwater, the sand stream generally can be restored by 

 pumping sand through a pipeline from the side where sand accumulates to 

 the eroded downdrift side. This type of operation has been in use for 

 many years at Santa Barbara, California. 



Even without a shore arm, an offshore breakwater reduces wave action 

 and creates quiet water between it and the shore. In the absence of wave 

 action to move sand, it is deposited and builds the shore seaward toward 

 the breakwater. The buildup serves as a barrier which also blocks the 

 movement of littoral materials. If the offshore breakwater is placed 

 immediately updrift from a navigation opening, the structure impounds 

 sand, prevents it from entering the navigation channel, and affords 



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