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Wetlands are also of value in
reducing the impacts of floods. Wetlands can reduce flooding by
intercepting storm runoff and storing it. Storage of flood water
reduces the sharpness of peak water flows (the peak flows generally
cause the most damage) and allows a slower discharge of water over a
longer period of time. This results in less severe flooding and less
flood damage. Wetlands associated with rivers generally provide the
most benefit in regards to flood control.
(adapted from Mitsch and
Gosselink 2000)
One heavily referenced case study is the Charles River in
Massachusetts. There is an estimated 8,400 acres of wetlands in the
Charles River basin that collects and stores flood water. It is
estimated that $17 million is saved annually be the presence of
these wetlands. This number is likely even larger if you consider
inflation and the increased amount of construction since this study
was completed in the early 1970s. It is obvious that some wetlands
can reduce the impacts of flooding.
The 1993 floods in the Upper Mississippi River basin caused over $16
billion in damages. Much of this flood damage has been attributed to
the loss of wetlands within the Mississippi River basin. Prior to
European settlement, there were enough wetlands to store floodwater
equivalent to 60 days of river discharge. Since that time, due to
the destruction of wetlands, storage capacity has been reduced to
about 12 days. It is estimated that even half of the original
wetland acreage would have been enough to prevent most of the $16
billion in damages that occurred in 1993. However, major changes in
policy would be needed in order to bring wetlands back to the level
needed to make serious headway in reducing flooding in the
Mississippi River basin.
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