for the steeper slopes, wliich infltieroGcl the author to assign a smaller 

 "intrinsic" coefficient of reflection p to the discontinuous slopeso 



Gonputations for the coefficient p from a miniinura of available data 

 for different types of structures from widely scattered sources shovred 

 considerable variation as e^cpected, but the number of cases involved was 

 insufficient for correlation* It appears in general, hoTiiever, that the 

 value of p is considerably less than the Oe8 and 0,7 used by the author 

 for the case of a smooth inpermeable slope. In li^^gure 6 there are summarized 

 test results made systematically on large scale models (l:^0) of seawalls 

 constructed of rock and artificial blocks, and comparison is made with com- 

 puted curves derived by equations 2 and 3 with p -valued at 0,33, The author 

 notes that in tlxLs case the Irribarren and Nogales formula "used for com- 

 putation of batter limit iTOuld no longer be suitable without adjustment. 

 In fact, the part effectively reflected wh-ich this formula gives for slopes 

 is very sharply inferior to 50 percent (about a thj.rd)," 



Conclusions presented by the author are s-ommarized below. The reflect- 

 ing power R of vrorks built a3-ong the coast, being the ratio of the ajiplitudes 

 of the reflected wave to that of the incident wave, varies according to the 

 georiBtrical form (slope) of the structiu'e and also mth the physical nature 

 of the s^orface in contact iri-th the wave. Equation 2 is apparently a correct 

 relationsiTip for determining the effect of form on reflecting poii-rer, and 

 shows that from a maximum value, or unity, the theoretical reflecting power 

 R' decreases rapidly xcLth decreasing slope, and decreases less rapidly icLth 

 increasing steepness of the incident wave. The factor of the physical nature 

 of the reflecting s-cur-face or the "intrinsic" coefficient of reflection p 

 varies as the turbulence developed on contact of the wave with the reflect- 

 ing surface. "For swells attacking the obstacle frontally or mth moderate 

 obliquity, its vaU-iie seems to oscillate around Oo8 for relatively smooth 

 batters, not very pernEable and not washed over (overtopped) by incident 

 wavesj it diminishes, the whole being subject to certain variations, for 

 rough batters, perineable or partly cleared (overtopped; by waves. In a 

 well studied case, this factor has then been found to equal about 0,33*" 



By use of the esqoression R = pR' it is possible for the m.axLriium wave 

 arplitude (the sum of the anplitudes of the incident and reflected waves) 

 to be determined iiranediately adjacent to the seaward face of a reflecting 

 structures To do thjLs it is necessary to know the steepness ratio of the 

 incident waves (preferably majdmum and minimum) ajid tre value for the 

 "intrinsic" coefficient of reflection. For the latter a value of 0*8 is 

 frequently suitable for smooth surfaces. Hoxirever for smooth surfaces with 

 steep slopes or vertical faces, where tixrbulence is reduced to a minimum, 

 a value of one may be chosen, in agreeri-Bnt vrith current practice, wliich 

 assumes the condition of clapotis where the maximujii amplitude near the 

 structure is t^'jice the ajplitud-e of the incident :rave. For exterior 

 coastal works constructed of enrocl<Tiients or artificial blocks, this co- 

 efficient p is much sr.ialler. Additional systematic tests are necessary 

 to finally fix its value, but teiiporarily a coefficient of 0,3 should be 

 considered as a minimum and a value of 0«6 as that assuming sufficient 

 conservsjncyo 



