EM 1110-2-1100 (Part II)
(Change 1) 31 July 2003
Figure II-2-3. Equivalent duration for wave generation as a function of fetch and
wind speed
EXAMPLE PROBLEM II-2-2
FIND:
The appropriate 100-year wind speed for a basin with a fetch length of 10 km.
GIVEN:
A 100-year wind speed of 19.9 m/s, derived from 3-hr synoptic charts.
SOLUTION:
Figure II-2-3 requires knowledge of both wind speed and fetch distance; however, reasonable
accuracy is gained by simply using the original wind speed and the appropriate fetch. In this case from
Figure II-2-3, the appropriate wind-averaging interval is approximately 90 min. Using information from
Figure II-2-1, the ratio of the highest 90-min wind speed to the highest 3-hr wind speed is given by the
relationship
U5400/U10800 = [-0.15 log10 (5400)+1.5334]/[-0.15 log10(10800)+1.5334] = 0.9735/0.9284 = 1.048
Thus, the appropriate wind speed should be 1.048 times 19.9 m/sec, or 20.8 m/sec.
II-2-6
Meteorology and Wave Climate
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