anticipated short-time beach losses caused by storms. Erosion caused by 

 storms generally results in a greater loss of beach material above the 

 mean low water level, because the superelevation of the water level (storm 

 surge) allows storm waves to act on the upper part of the beach. 



Other factors in planning and design are the depth of wall penetra- 

 tion to prevent undermining, tie backs or end walls to prevent flanking, 

 stability against saturated soil pressures, and the possibility of soil 

 slumping under the wall. 



5.3 PROTECTIVE BEACHES 



5.31 FUNCTIONS 



Beaches of suitable dimensions are effective in dissipating wave 

 energy, and, when they can be maintained to proper dimensions, afford pro- 

 tection for the adjacent upland, and are classed as shore-protection struc- 

 tures. Such beaches dissipate wave energy without causing adverse effects. 

 When studying an erosion problem, it is advisable to investigate the feasi- 

 bility of mechanically or hydraulically placing borrow material on the 

 shore to restore or form, and subsequently maintain, an adequate protective 

 beach, and to consider other remedial measures as auxiliary to this solu- 

 tion. The method of placing beach fill to ensure sand supply at the re- 

 quired replenishment rate is important. Suitable beach material may be 

 stockpiled at the updrift section of the problem area where stabilization 

 of an eroding beach is the problem. The establishment and periodic 

 replenishment of such a stockpile is termed avtifioi-al headh nourishment. 

 If the solution of a problem requires restoration of the eroded beach and 

 its stabilization at the restored position, fill is placed directly on the 

 eroded beach. Then artificial nourishment is accomplished by stockpiling. 

 When conditions are suitable for artificial nourishment, long reaches of 

 shore may be protected at a cost relatively low compared to costs of other 

 adequate protective structures. An equally important advantage is that 

 artificial nourishment directly remedies the basic cause of most erosion 

 problems - a deficiency in natural sand supply - and benefits rather than 

 damages the shore beyond the immediate problem area. An added consideration 

 is that the widened beach may have value as a recreation feature. 



Under certain conditions, a properly designed groin system may im- 

 prove a protective beach. This method must be used with caution, for if 

 a beach is restored or widened by impounding the natural supply of litto- 

 ral material, a corresponding decrease in supply may occur in downdrift 

 areas with resultant expansion or transfer of the problem area. Detri- 

 mental effects of groins may usually be prevented by placing artificial 

 fill in suitable quantity concurrently with groin construction; such stock- 

 piling is called filling the groins. Groins may be included in a beach 

 restoration project to reduce the rate of loss and thus the nourishment 

 requirements. When groins are considered for use with artificial fill, 

 their benefits should be carefully evaluated to determine their justifi- 

 cation. Such justification could be that groins would reduce annual 

 nourishment costs in excess of the groin annual charges. (See Section 

 5.610 Economic Determination for Groin Construction.) 



5-7 



