On the other hand, since (see eq. 16) 
0p 30p ( Ho 
ARTE PST, 0.25 + 5.5 —= (19) 
and by taking into account equation (11) 
lor 1 one 
—o = (20) 
a bie ( Ys/,.) iH 
Finally, by inserting equation (20) into equation (19) 
O25 = 5.5 1o/, 32 
Jone) y t Lo 9 Ys 
(21) 
= 1 6/5 oo 
In case of wave diffraction, the wave height varies significantly along a wave 
crest. Then, the previous refraction coefficient, Kps has to be replaced by 
a combined diffraction-refraction coefficient, such as K,K,. (A diffraction 
current in opposite direction to a longshore current takes place at a distance 
from the end of the groin.) The variation 9Kp/dx is much larger than dKp/dx. 
Therefore, in analogy with equation (18) 
3Q¢ dp OS 2 
— = nix (2x2 cos 2a, =— + 2Kp == sin 20, (22) 
In a diffraction zone, az, is due to the sum of variation of shoreline direc- 
tion, tan7! dY¢/9x, and because of diffraction the rotation of the wave crest 
around the end of the groin, §& (Fig. 6). 6 is the angle which has the end 
of the groin as apex and extends from the limit of the shaded area to the con- 
Sidered location defined by x. Figure 6 shows that © = ajo - 8' and 6' = 
tan7! x/2, where 2% is the length of the groin. Therefore, 
= em! 28 Ss wenel & 23 
apy waean = + A an (23) 
1 Oeste Change Une er eL (24) 
OR rox et (x 2) 
and, differentiation equation (23) and inserting equation (24) 
30 a*y 
SDAIN tens, San Sepp live Tce wale. (25) 
Q 
Se a C2) 
where dKp/ ox is the coefficient of variation of wave height due to combined 
effects of wave diffraction and wave refraction. It also includes the effect 
of diffraction current. 
An empirical formulation for determining the combined effect of diffraction 
and refraction is more suitable to quantitative analysis of a real sea spectrum 
19 
