The wave length L at the depthjd, of the breakt-rater tip iraist be found by 

 computing the ratio d/Lo I'L ~ the deep water wave length), hj referring 

 to Table 1 of Appendix D .'or the corresponding value of d/L and dividing 

 d by this ratiOo The diagram itself must then be scaled up or doTim so that 

 the distance from j/L ~ to y/L = 1 corresponds to one wave length on 

 the scale of ths chart on which the diagram is to be drawno 



50, The diffraction diagram is then placed so that the x/L = 

 ordinate lies in the direction of wave approach, with x/L positive values 

 on the sides of the breakwater to"war'd the protected ai'-ea in the break- 

 water's leeo The lines labelled "wave crests" then represent positions of 

 first, second^, etc. diffracted wave crests from the brealn-rater. The lines 

 labelled K' ax-e lines of equal, decreased wave height. That is, along 

 the K' = 0,20 line for example wave heights ar'e two- tenths of their values 

 outside the breala^ratsr, 



5'1. Waves Passing a G ap of Width Less than Five W?ve Lengths . - The 

 solution for this proble"m (/i^^pendix E) is more coirplex, and it is not 

 possible to construct one diagram for all conditions. A new diagram must 

 be drawn for each different ratio of gap width to Xirave length. One, for 

 a gap width to x-rave length ratio of 2.00 (see Appendix E) is shown in 

 Figure 21, which figure also illustrates its use. Figures 22 tlirough 31 

 show lines of eaual diffraction coefficient for gap mdth (E) to wave length 

 (l) ratios of B/l. of 0.50, 1.00, l.ltl, 1.61;, 1.78,^2.00, 2.^0, 2.95, 3.82 

 and 5.00 draxrn for a somewhat more complex solution of the diffraction 

 problem than that in Appendix E. In all but Figures 27 j for B/L = 2.00, 

 the wave crest lines have been eliminated. Wave crest lines are usually 

 only of pictorial use. One-half the diffraction coefficient lines have 

 been elimi_nated from these figures but the diffraction coefficients 

 ax'e syraraetrical about the x/L = ordinate, thus the diagrams may be com- 

 pleted by folding the diagr-am about that ordinate. 



52, ,^'g-?.g_s:_..Passing a Gap of Width Greater Than Five Wsve Lengths . - 

 >Jhere the breaktirater gap xd.dth is greater than five wnve lengths, the 

 diffraction effects of each xfing are essentially independent^ and the 

 diagram (Figure 19) for a single breaki-rater inay be used to define the 

 diffraction cha}-.''acteristics in the lee of both wings. (See Figure 32) 



S3o Diffraction at a Gs.p - Oblique Incidence . - When the waves 

 approach at an angle to the breal-ciirate • gap centerline, an appro:d.mate 

 appraisal of diffracted wave characteristics may be made by considering 

 the gap to be as wide as its projection in the direction of incid.ent 

 wave travel, Diffraction diagrams should be drawn in the manner of the 

 preceding sections but using this effective gap instead of the true gap. 



5h. Ref raction 3jid Diffraction Com bined. - If the bottom seaward 

 and shore wax'd of a brealiwater is not flat - the usual case - refraction 

 as well as diffraction will talkie place. Though a unified theory of the 

 two has not yet been devised^ an approximate picture of wave changes may 

 be drawn by 5 (l) coristructing a refraction diagram to the breakifater, 



32 



