land behind them. Even when breached by severe storm waves, dunes may 

 gradually rebuild naturally (over a period of several years) to provide pro- 

 tection during future storms. 



Continuing encroachment on the sea with manmade development has often taken 

 place without proper regard for the protection provided by dunes. Large dune 

 areas have been leveled to make way for real estate developments, or have been 

 lowered to permit easy access to and view of the beach area. Where there is 

 inadequate dune or similar protection, storm waves may attack beach-front 

 structures (see Fig. 1-10), and wave overwashes may flood and damage backshore 

 property. Even when coastal flooding does not occur, high storm surges and 

 associated waves can undermine and damage structures placed too close to the 

 beach (Fig. 1-11) . 



When the natural protection system fails during large storms, the first 

 solutions frequently chosen are quasi-natural methods such as beach nourish- 

 ment or artificial sand-dune building. Such solutions retain the beach as a 

 very effective wave energy dissipater and the dune as a flexible last line of 

 defense. However, even these methods provide only a temporary solution to 

 chronic long-terra erosion caused by the diminishing supply of sediment in the 

 littoral system and by the slow sea level rise. 



The method of placing beach fill to ensure sand supply at the required 

 replenishment rate is important. Where stabilization of an eroding beach is 

 the problem, suitable beach material may be stockpiled at the updrift sector 

 of the problem area. The establishment and periodic replenishment of such a 

 stockpile is termed artificial beach nourishment. To restore an eroded beach 

 and stabilize it at the restored position, fill is placed directly along the 

 eroded sector, and then the beach is artificially nourished by the stockpiling 

 method. 



When conditions are suitable for artificial nourishment, long reaches of 

 shore may be protected by this method at a relatively low cost per linear 

 meter of protected shore. 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 adja- 

 cent shore. An added consideration is that a widened beach has value as a 

 recreation feature. One of the most recent beach restoration projects began 

 in 1977 along 17 kilometers (10.5 miles) of beach in Dade County, Florida 

 (including Miami Beach). This project is shown in Figure 1-12. 



Where beaches and dunes protect shore developments, additional protective 

 works may not be required. However, when natural forces do create erosion, 

 storm waves may overtop the beach and damage backshore structures. Manmade 

 structures must then be constructed to provide protection. In general, meas- 

 ures designed to stabilize the shore fall into two classes: (1) structures to 

 prevent waves from reaching a harbor area (e.g., breakwaters, seawalls, bulk- 

 heads, revetments) and (2) manmade structures, such as groins and jetties, 

 used to retard the longshore transport of littoral drift. These may be used 

 in conjunction with seawalls or beach fills or both. 



Separate protection for short reaches of eroding shores (e.g., individual 

 shore-front lots) within a larger zone of eroding shore, is a difficult and 



1-19 



