hy
do cities across North America spend tens of millions of dollars on
preserving their wetlands? Because the costs of replacing the function
of wetlands with stormwater and water treatment infrastructure are on
the order of 10 times more.
Nature does for free what cities need
most: flood control, groundwater recharge, the storage and
purification of water, habitats for birds and animals, recreation, and
tourism. Forested wetlands capture, store, and purify water. They
provide habitat to a diverse group of plants and animals, including
migratory birds. They represent the water we drink, the air we
breathe, and the outdoor recreation spaces we enjoy. Urban wetlands
act as a sponge and are integral to the watersheds of cities. Even in
cities that get their drinking water from lakes or rivers, the
integrity of watersheds surrounding the city help filter the urban
runoff before it enters these bodies of water.
Larch swale in the UNB Woodlot,
Fredericton.
(Photo: Mark D'Arcy)
Stormwater pipes are no substitute for
intact wetlands and forests within our city limits. The importance of
wetlands for flood control cannot be understated. One acre of wetland
can hold 1-1.5 million gallons of floodwater. In June 2008, the
500-year flood in Cedar Rapids, Iowa, was a warning to the collision
course between climate change and the loss of upstream wetlands to
development. A severe rain event of 46 cm (18 inches) in 10 days
saturated the soil to its carrying capacity and then the runoff
swelled the banks of Cedar River. As wetlands are infilled and paved
over, their rainfall capture ability is lost.
Wetlands are our insurance policy
against climate change. The severity of runoff from heavy rain events
is affected by the size and layout of wetlands and the surrounding
vegetation. The Toronto Ravine System is not only a recreational jewel
but it cushioned the city from catastrophic damage in October, 1954,
when Hurricane Hazel dumped 12 cm (5 inches) of rain on the city in a
day. Saint John received the same amount of rain in 2008 with
Hurricane Hanna, resulting in severe flooding. The City of Saint John
is now studying its drainage patterns in order to limit development in
areas above which flooding problems exist.
But New Brunswickers can learn from
these floods. The UNB Woodlot is a 3800-acre forested wetland situated
at the top of Fredericton and is equal to the size of the south side
of Fredericton and Lincoln in the valley below. Just like an egg
cracked over a person's head, rain captured by the UNB Woodlot
supplies the headwaters and tributaries of Corbett Brook, Phyllis
Creek, Garden Creek, and Baker Brook watersheds, and smaller
watercourses that flow through Fredericton and towards New Maryland.
Not only do these forested wetlands contribute to our aquifer - the
sole drinking water supply for the City of Fredericton - but they act
as a giant sponge during severe rain events and slowly release the
water to surrounding forests and aquifers that supply our drinking
wells.
Pitcher plant in Regent Bog, UNB
Woodlot, Fredericton.
(Photo: Mark D'Arcy)
If this water absorbing capacity of
wetlands is fragmented or lost altogether by development, the
taxpayers of Fredericton would be saddled with the cost to build
replacement infrastructure for storm water management. Unfortunately
storm water pipes and retention ponds are an inferior solution so we
would also be saddled with flooding costs.
In this electronic age, the natural
world is important for the healthy emotional and intellectual
development of our children. Urban forests are magnets for
exploration, adventure, hiking, mountain biking, and learning about
nature. Wetlands are natural teaching classrooms for our children.
Thousands of grade 4 children have visited the Ducks Unlimited Corbett
Brook Marsh in the UNB Woodlot to learn about the diversity of plants
and animals in these unique habitats. Wetlands also serve as outdoor
labs and research for students in colleges and universities.
Beaver lodge in the UNB Woodlot,
Fredericton.
(Photo: Mark D'Arcy)
The future climate scenarios for the
Fredericton/New Brunswick region are sobering. Conservative computer
models by Environment Canada predict major changes this century:
severe rain events are expected to increase in number and severity
with climate change; a 30% increase in winter precipitation; twice the
amount of winter runoff; significant increase in freeze-thaw cycles
(in winter); lower summer/fall runoff by one-half; a 3.1 to 5.9 *C
increase in mean winter temperature; and a 2.4 to 5.1 *C increase in
mean spring temperature. The combination of severe rain events with
more winter melt will increase our risk of floods. Rain-saturated soil
provided the perfect conditions for the great spring flood of 1973 in
New Brunswick. Also, significant increases in rainfall and wind speeds
of hurricanes will both be fueled by warmer water temperatures in the
Atlantic. Notable hurricanes that caused flooding in New Brunswick
include Carol (1953), Edna (1954), Gladys (1968), Belle (1976), Bertha
(1996), and most recently Hanna (2008). And as this article is
written, Hurricane Kyle was forecast to deliver up to 10 cm of rain
over New Brunswick - a day after receiving already 5 cm of rain - but
fortunately we did not take a direct hit.
Urban forested wetlands are well worth
preserving. Our governments have an obligation not to pay for inferior
solutions when nature provides a priceless solution for free.
