Region 1: EPA New England
Wetlands Can Help Reduce Flooding
Note: EPA no longer updates this information, but it may be useful as a reference or resource.
By Robert
W. Varney
June 1, 2006
Talk about extreme weather! First, rain-swollen rivers flooded dozens of New England towns last October. Then, in the past several weeks, one of the driest spring seasons in decades transformed into two weeks of heavy rainfall, causing major flooding in northeastern Mass. and portions of southern New Hampshire and Maine.
Can our natural environment keep pace with such extremes? The answer may be "yes," so long as we keep wetlands around to help mitigate the effects of extreme weather.
This story begins in the upper reaches of every watershed in New England. Nestled there are small, sometimes almost imperceptible, wet pockets and tiny rivulets - referred to by scientists as headwater wetlands. It's a grandiose name for a modest resource, especially given their history of being unnamed, under-mapped, and generally overlooked. But appearances can be deceiving, and these little ecosystems often provide a value disproportionate to their size.
Consider how critical small headwater wetlands are to the healthy functioning of downstream rivers and lakes, including the ability to provide natural flood control. When headwater wetlands are left in their natural state, they store enormous amounts of rainwater, runoff and snow melt.
During severe storm events, headwater areas and wetlands adjacent to a river's edge detain storm runoff, temporarily storing floodwaters and slowly releasing them downstream. Dense wetland vegetation also provides enough friction to slow the flow of water entering an already-swollen riverway. The combined action of storing and slowing of floodwater lowers flood heights, reduces velocity, and minimizes damage to downstream communities.
Conversely, the water-storing ability of headwater wetlands during high flows can also help quench the thirst of water-starved streams during drought. Water in streams and rivers comes from several sources, including water held in the soil, runoff from precipitation and ground water.
When we have a dry season, as much as 95 percent of a stream's flow may come from ground water. Here's where headwater wetlands come in handy: these many small upstream wetlands have the largest surface area of soil in contact with available surface water - providing the greatest opportunity for water to soak into the ground and recharge ground water supplies. As water levels in streams and rivers begin to drop during the summer months, water stored in adjacent headwater wetlands is released slowly into the stream and river system, maintaining healthier flow levels for fish and boaters alike.
Wetlands provide valuable ecosystem services to society, offering key habitat to wildlife, enhancing our landscape with their natural good looks - and they do it all at no cost to taxpayers. Of course, wetlands can only do so much without our cooperation.
When we develop previously untouched land, we also increase impermeable surfaces - such as roads and parking lots – meaning that more precipitation runs off directly to rivers and streams, rather than soaking into the ground. This short-circuits the ground water recharge process. By eliminating wetlands, we allow more water to flow rapidly downstream, leading to more intense and frequent flooding conditions such as those we've experienced within the past year.
Why not take advantage of the free flood protection afforded by wetlands? Let's protect our remaining wetlands in New England so they may continue to protect us.
More information on wetlands in New England.
Robert W. Varney is regional administrator of EPA's New England Office in Boston.