Cold Weather Flooding Season

Winter through early spring is the time of year when middle Tennessee is most
susceptible to flooding. There are several reasons for the increased risk of
flooding. As the upper-level wind patterns shift with the season, storm systems
pass through the Tennessee Valley more often, increasing the chance for
precipitation. Most of middle Tennessee averages between four and five inches of
precipitation per month during November and December. Another reason for the
cold season flooding is that when the growing season ends, vegetation requires
less moisture from the soil and colder soil temperatures cause rainfall to
�run-off� more quickly into river and stream channels. During the warm or
growing season, a three-inch rainfall in twenty four hours may not produce
flooding, whereas the same three-inch rainfall during the cold season could
cause significant flooding.
Some middle Tennesseans may remember the
Cumberland River flood of March, 1975. A storm system remained nearly stationary
over the Lower Cumberland River Basin for four days. Rainfall averaged 6.7
inches over most of the basin during a sixty-hour period between March 11-14.
Several stations reported storm total rainfall amounts between eight and nine
inches. As a result of the persistent heavy rain, major flooding occurred along
the Cumberland River. In Nashville, extensive residential and industrial
flooding occurred as the Cumberland River rose to a height of 47.64 feet -- 7.64
feet above flood stage. The March, 1975 flood was one of the most severe floods
on several tributaries to the Cumberland River as well. The Stones River,
Harpeth River, and Red River all experienced severe flooding.
More recently,
significant flooding occurred on the Duck River during January, 2002. As a
result of very heavy rain, water levels rose well above flood stage at
Shelbyville, Columbia, Centerville, and Hurricane Mills. Columbia experienced
its worst flooding since 1991, as the river crested at 45.6 feet -- 15.6 feet
above flood stage.
Why should you be concerned about flooding? Floods kill
more people in the United States than any other form of severe weather. Flood
waters can roll boulders the size of a car, tear out trees, destroy buildings
and bridges, and pose a significant threat to human lives. While most floods
cannot be prevented, there are steps you can take to protect life and property.
At a minimum you should know where you are in relation to rivers and streams.
Stay informed during persistent rain events by listening to NOAA Weather Radio,
local television, or radio for the latest information on flood watches and
warnings. And have an evacuation plan in place BEFORE flooding occurs.

Michael MurphyService Hydrologist- National Weather Service, Nashville 2002