EM 1110-2-1100 (Part II)
(Change 1) 31 July 2003
EXAMPLE PROBLEM II-2-7
FIND:
The significant wave height at the end of this fetch, assuming that the duration of the wind is sufficient to
generate fetch-limited waves (from Figure II-2-2, this is found to be greater than about 1.25 hr).
GIVEN:
A constant wind speed of 15 m/sec over a fetch of 10 km in a basin with a constant depth of 3 m. (Note: as
pointed out in the previous section on winds, wind speeds tend to increase with fetch over a fetch of this size, so
care should be taken in estimating this wind speed)
SOLUTION:
OPTION 1 - Use ACES
OPTION 2 - From Figure II-2-24 the fetch-limited peak wave period is about 2.7 sec, from Equation II-2-39,
the limiting wave period in 3 m is 5.4 sec; therefore, Tp = 2.7 sec and Hm0 = 1.0 m (deepwater values).
EXAMPLE PROBLEM II-2-8
FIND:
The significant wave height at the end of this fetch.
GIVEN:
A constant wind speed of 25 m/sec over a fetch of 50 km in a basin with a constant depth of 1.6 m.
SOLUTION:
OPTION 1 - Use ACES
OPTION 2 - From Figure II-2-24, the fetch-limited peak wave period is about 5.8 sec, from Equation II-2-39,
the limiting wave period in 1.6 m is 4.0 sec; therefore, the waves stopped growing at this limit. This corresponds
to a fetch of 20 km at this wind speed; thus, the final values of Tp and Hm0 are 4.0 sec and 2.1 m (using the 20-km
fetch and 25-m/sec wind speed in Figure II-2-23). However, this value exceeds 0.6 times the depth, so the final
answer should be 0.8 m.
II-2-54
Meteorology and Wave Climate
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