APPENDIX B: EXAMPLE DESIGN PROBLEMS 



1. The example problems contained in this Appendix illustrate several 

 types of evaluations which may be appropriate for designing a detached break- 

 water project. Although the scenarios are slightly contrived, they emphasize 

 the importance of understanding the local wave climate, local sediment trans- 

 port history, and the project's intent. General breakwater design guidance 

 can be derived from examining existing projects. Selection of a design con- 

 figuration for any particular project is ultimately a qualitative art. The 

 plans presented in these example problems should subsequently be tested via a 

 diffraction analysis and a numerical and/or physical model. 



Problem 1: Design of a Single Tombolo 



Problem 



2. An important building is threatened by erosion because of an updrift 

 harbor blocking the predominant longshore transport and offshore losses asso- 

 ciated with frequent storms. The owners of the building own large segments of 

 beach in each direction and are not concerned with any effects the protection 

 may have on neighboring shores. The area to be protected is 100 m long and is 

 presently only 30 m from the normal high tide line. The predominant breaking 

 wave climate has a period of 7 sec, a height of 1.2m, and produces a slight 

 longshore transport from left to right, as shown in Figure Bl. The average 

 nearshore slope is 1 on 50 and the diurnal tide range is 1.0 m. The design 

 storm surge is approximately 2.0m and the design breaker height is 4.0 m. A 

 protection scheme can be designed by using a detached breakwater (Figure Bl) . 

 S olution 



3. Because the effects on the adjacent shoreline are not important, and 

 the task is to provide maximum protection to a short segment of beach, the 

 structure is designed to develop a single tombolo. The location of the normal 

 breakwater line (for H. = 1 . 2 m) is estimated to be approximately 75 m off- 

 shore. To trap as much sediment as possible while placing the structure in a 

 reasonable water depth, it is suggested that the breakwater be located outside 

 the breaker line, 100 m offshore at -2.0 m. To ensure tombolo formation a 

 structure length of 250 m is selected, a little more than twice the distance 

 offshore. This length will make the tombolo large enough to provide good 



Bl 



