Shore Protection Methods 



Frequently -we find that the natural conditions at a beach are not in 

 stable adjustment and that progressive erosion of the beach is underway. 

 In such cases it is sometimes found that the eroding condition can be ar- 

 rested by the construction of shore protection structures to check the re- 

 moval of material from the beach or by increasing the supply of material 

 to the shore <. 



Presently known feasible methods of modifying supply and loss rates 

 are limited with one exception to various types and placements of structures. 

 We know these by their designations as breakwaters, jetties^ bul^eadSj sea- 

 wallSj revetments and groins; artificial nourishment is the non-structural 

 excdption o 



Breakwater's as the name iii5>lieSj are energy dissipating or wave inter- 

 rupting structures employed to break or c^ssipate water waves and thus pre- 

 vent their incidence on an area it is desired to protect „ Their effect on 

 material movement arises entirely from modification^ usually in the form of 

 reduction^ of "the incident energy of water waves » 



Bulkheads 5 seawalls and revetments constitute a class of structures 

 whose chief function is to substitute non-erodible for erodible material and 

 concurrently provide for energy dissipation o Their effect on the movement of 

 material is direct^ by the substitution of materials, and indirect <, by the 

 modification J sometimes dissipativej, of the energy in incident waves or cur- 

 rents* They are employed widely and are particularly suited for the preser- 

 vation of a definite land-water boundary at a given location » There is 

 almost always an increase in degradational action associated with their use<, 



Groins are structures designed and built to intercept and retain ma- 

 terial in littoral movement and thus modify rates of supply and loss of 

 material directly o Their influence on the energy pattern is almost entirely 

 indirect^ resulting from a reorientation of the shore line in a direction 

 more normal to wave approach. Accordingly, groins should be considered as 

 more than simple barriers to sand movement. Because of this action they 

 may cause an appreciable modification of the entire littoral regimen. 



Jetties are multi-purpose structures, whose functions may include those 

 of breakwaters 5 groins and bulkheads. Although they are usually associated 

 with navigation improvements at inlets^ river mouths or harbor entrances^ 

 they frequently result in major physiographic changes. Analysis of the 

 effects of jetties on shore lines is one of the most difficult of shore 

 problems to solve in detail^, the ease with which general features of the 

 effects can be predicted belying the difficulty of a detailed analysis. 



Artificial nourishment is adequately described by its name as a method 

 of supplying beach material additional to that available naturally. It is 

 useful for rehabilitating or rebiiilding beaches, for maintaining a desired 

 existing beach condition^ or for improving to a large or small extent exist- 

 ing conditions. Although gaining in popularity as a shore control method^ 



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