(a) Snell's law. 
ee ee 1 
CO Sani: ST /25 (2) 
(b) Wavelength (dispersion relation). 
L 27d 
2 = tan n (+) (13) 
O Db 
(c) Conservation of energy flux between wave orthogonals (G is 
the group velocity). 
2 = H2 14 
HS cos a,G, = He cos a,G, (14) 
(d) Breaking criteria. 
Hy, 21d 
— = 0.14 tanh (15) 
Lp Lp 
From these equations, it has been shown (Le Mehaute and Koh, 1967) that when 
a, remains smaller than 50°, ap could be approximated as 
O 
9.25 + 5.5 Mo 16 
=~ Jie a 5 — 
On =A cs (16) 
where 
aie 
lL. = 
@ 27 
Therefore, the refraction coefficient 
ae COS Ap 1/2 
A COS Ob 
could be written, inserting oa, as given by equation (11), and ap as given 
by equation (16) 
2) 
cos(a - tan7! 9Y, ae 
Tee ae fe ee ee a Nd = (G7) 
fi ( ois: 2aH2 
cos |(a - tan Ye/, ) (0.25 SS Oloc hy of, 2) 
( Be 2 
Now it is possible to formulate the variation of littoral drift over a distance 
Ax = unity. From equation (9) 
2Q¢ 
ox 
‘Db 2 dKp if 
5 + AH52Kp ae Zap (18) 
= AH2K% 2 cos 2a ee 
oR Dia 
where 
