MIL-HDBK-1011/1
Monsoons are one of the most important rain-producing currents on
the globe. Intensity and duration are not uniform year to year. A heavy
season with floods may be followed by several seasons with below-average
precipitation, crop failure, and famine. Research and design for the extreme
conditions brought on by monsoons.
1.5.5
Storm Surges. In one type of storm surge, strong winds pick up
water along a coast causing sea level to rise. The approximate height of this
storm surge can be predicted based on wind speed and direction, fetch, water
depth, and the shape of the ocean basin. Other factors, such as currents,
astronomical tides, and seiches set up by storms, complicate the calculations.
a) A second type of surge is a large wave that moves with the
storm, typhoon, or hurricane which caused it. First comes a gradual change in
water level, the forerunner, a few hours ahead of the storm's arrival. It is
apparently caused by the regional wind system and may cause sea level to fall
slightly along a wide stretch of coastline.
b) When the typhoon or hurricane center passes, it causes a sharp
rise in water level called the surge. This surge usually lasts about 2-1/2 to
5 hours; rises in sea level of 12 to 16 feet have been observed -- usually
slightly offset from the storm's center. Combined with extremely high waves
generated by the storm surges can be extremely destructive.
c) Following the storm, sea level continues to rise and fall as
oscillations set up by the storm pass. They are more or less free surface
waves and have been termed the wake of the storm, like the wake left by the
passage of a ship through the water. The sea surges can be quite dangerous,
particularly because they are often not expected once the storm itself has
subsided.
d) Tropical storms, typhoons, and hurricanes frequently cause
storm surges along the Gulf Coast of the United States. In 1900, Galveston,
Texas was destroyed and about 6,000 people were killed by a storm surge
resulting from a hurricane. In 1969, Hurricane Camille, the second strongest
recorded storm to hit the Gulf Coast, caused
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.4 billion in damage; even with
advance warning, it killed 256 people, A disastrous storm surge occurred in
1876 in the Bay of Bengal when 100,000 people were killed. In 1970, another
storm surge hit the same area, killing an estimated 500,000 people.
e) Designers working on projects sited near coastlines are
responsible for researching past surges in the project area and evaluating the
effects of future surges on their project.
1.5.6
Floods.
Floods happen when water rises above a flood plain level
and damage begins to occur. Flood plains can be channels, deep and wide, or
many miles wide and shallow, such as an alluvial plain. The encroachment of
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