a. In Figure 58 let B represent the beach at a water depth of 

 30 feet, E the beach at the point of slope break (say) at a depth of 

 $ feet, and C the present position of the berm crest. If at A it is 

 desired to built a structure whose economic life is (say) 50 years, 

 and it is found that n is the annual loss of beach width' at the berm, 

 then in 50 years without the wall this berm will retreat a distance 

 50 n to point Dj 



b. From D to the elevation of point E draw a profile DF parallel 

 to CE, and connect points B and F. This line DFB will represent the 

 approximate profile of beach after 50 years, without the presence of 

 the wall. The new beach elevation at the wall's location will be 

 approximated by point A'. Similar calculations may be made for 

 anticipated short time beach depredations caused, for example, by 

 storms . 



PROTECTIVE BEACHES 



129. Functions. - Beaches are the most effective means of dissipating 

 wave energy. They provide protection to upland property, while maintaining 

 ivll recreational use of the shore area. They may be placed artificially 

 or may be accumulated by groins. Direct placement of a beach fill involves 

 the artificial deposition of a sand fill directly in front of the specific 

 reach of upland the fill is designed to protect, with secondary consideration 

 being given to the beneficial effects of the deposit on adjacent areas. 

 Conversely, artificial nourishment involves provision of a sand supply to 

 augment the natural supply of littoral material. Protection is thereby 

 provided to long reaches of upland through maintenance of protective beaches 

 by natural forces, with secondary consideration being given to the beneficial 

 use of the sand supply itself. 



130. For artificial nourishment, the supply is ordinarily in the form 

 of a feeder beach, which, in eroding through the action of littoral 

 forces, increases the quantity of material in littoral transport. Attempts 

 have been made at Long Branch and Atlantic City in New Jersey and at Santa 

 Barbara in California to nourish an eroding beach by depositing material in 

 relatively deep water, depending on the action of natural wave forces to 

 move the material shoreward to the beach. Although observations made in 

 these tests indicate that this method will not provide nourishment at a 

 suitable rate to justify its general use, observations over a longer period 

 of time may indicate a benefit to some portion of the shore, possibly at 

 some distance from the location of deposit. 



131. Limitations . - The provision of beaches for protection of upland 

 areas and for beneficial use has two distinct limitations^ (l) beach 

 material must be available for initial construction and subsequent maintan- 

 ance, and (2) the annual cost of maintenance is generally high, unless a 

 considerable length of shore is involved. 



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