fetch to the end of the decay distance, itis assumed Substituting for T from (87): 
that the disturbance travels at half the wave dH pee dT: 
velocity. The significance of this assumption is Fife ar Ie 
examined in the next section. It follows 
FED dy Am (Ft? dx and integrating again from z=F to r= F+D, ; 
of, C25 Gg Jr TF se) tte 
| Hp_(Te) * roy 
According to (87) oar 
di Le Equations (88), (90), and (92) are presented in 
Po 8a°Ar figure 12, the nondimensional decay graph. 
Intensity and distance of storm from which swell 
ine le ian ; page ‘ : 
To omar 1S (90)  comes.—Sometimes it is desirable to estimate 
; ; . properties of the storm from wave observations 
Wave height and distance from @ generating in the decay region. Equations (88), (90), and 
area.—From equation (86a), considering that (92) are not suitable because the unknowns D 
and 
dE /E=2dH/H, one obtains and 7’ appear on both sides of the equation. 
1 dH Te Rearranging terms and solving for D, tp, and U* 
eda Oa : (91) in terms of the observed quantities Hp, Tp, and 
DECAY GRAPH 
Saal nal iat 
8 all | } | 
em| 
T 
| | 
16 | 6 
| 
| 
War. ° 
7 4 14 
| 
1 
2 1 2 
War t = i t 
T | | 
ay? | | aa ] 1 1 + c 
H | hr 
M4, Healt | 
oe | | | it f | oO 
oO6 
HO/ a, o re 
a ee | | oa 
| | | | 
] | T 1 T ] ] 1 T 
02 1 esl th | o2 
] 
| | 
| | | | 
| | | [os | 
| | 
MOROCCAN | ut | 
BERKELEY ] T 
PENDEEN - 610% 
POSSIBLE RANGE OF 
td/Tr DUE TO TIME 
INTERVAL BETWEEN 
OBSERVATIONS, 
3 
Oe 
a | 
Arle pale 
WI? 
Figure 12.—Period and height of swell at end of distance of decay, and travel time represented by moodimensicne! 
parameters. Theoretical relationships shown by curves; observations by symbols. 
28 
