Climate Change: More Intense Rains Could Swamp
Chicago's Aging Sewers
By Michael Hawthorne
April 21, 2011
In a city built on a swamp, where rainstorms already
flood basements and force sewage into Lake Michigan and
local streams, climate change could make Chicago's
chronic water pollution woes even worse.
Researchers hired by Mayor Richard Daley's office
estimate that intense rainfall will happen more
frequently in the not-so-distant future because of
warming global temperatures, challenging the region's
aging sewers and the troubled Deep Tunnel project more
Rains of greater than 2.5 inches a day, the amount that
can trigger sewage dumping into Lake Michigan, are
expected to increase by 50 percent between now and 2039,
according to a study by scientists from the University
of Illinois at Urbana-Champaign and Texas Tech
University. By the end of the century, the number of big
storms could jump by a whopping 160 percent.
Another group of researchers studying Milwaukee's sewers
recently concluded that heavy rains caused by climate
change could lead to a 20 percent increase in the number
of sewage overflows, a troubling sign for Chicago,
Cleveland, Detroit and other industrial cities
throughout the Midwest with similar systems.
"We've already seen an increase in these extreme weather
events, especially in the Midwest and Northeast," said
Don Wuebbles, a U. of I. climatologist who co-authored
the Chicago study. "Chicago has had two 100-year storms
in three years. Iowa has had three 100-year floods in
less than 20 years. That's telling us something."
As more research points to a changing climate -
including bigger rains followed by periods of drought -
local officials are grappling with the likelihood that
Chicago will need more solutions beyond the $3 billion
Deep Tunnel project, a subterranean network of giant
sewer pipes and cavernous reservoirs that now isn't
expected to be completed until 2029.
They aren't sure what those solutions are or how much
they will cost, but officials at the Metropolitan Water
Reclamation District and City Hall are hiring engineers
to evaluate how the existing labyrinth of sewer pipes
and flood-control reservoirs will handle the projected
increase in big storms.
The Tribune reported last month that nearly four decades
after taxpayers started paying for the Deep Tunnel, one
of the nation's most expensive public works projects,
billions of gallons of bacteria-laden sewage and storm
runoff still frequently pour into the Chicago River and
suburban waterways after storms.
Experts are finding the system can capture rainfall of
less than two-thirds of an inch, a typical summer
shower. Anything bigger than that forces a mix of
stormwater and human and industrial waste out of
overflow pipes into waterways and can cause sewage to
back up into basements.
If a storm is big enough, officials allow the muck to
flow into Lake Michigan, the source of drinking water
for 7 million people in the city and suburbs. Long
considered the sewage outlet of last resort, the lake
has been hit harder during the last four years than it
was in the previous two decades combined, records show.
A deluge that hit July 24 highlights what could soon
happen more frequently.
In less than 24 hours, one of the most intense downpours
in Chicago history swamped expressways, soaked basements
and flooded entire neighborhoods. More than 8 inches of
rain fell so hard and so fast that the Deep Tunnel
couldn't handle the surge of stormwater.
When a noxious mix of runoff and sewage threatened to
spill over the banks of the Chicago River and other
streams, local sewer officials made a last-ditch attempt
to relieve the pressure: They opened locks separating
the river from Lake Michigan and dumped more than 6
billion gallons of disease-causing, beach-closing, fish-
killing waste into the lake.
"There is no doubt that things are going to get
tougher," said Marcelo Garcia, a U. of I. hydrological
engineer who is studying the effectiveness of the Deep
Tunnel. "I like to think of the entire system as a giant
bathtub. They built a really big bathtub to collect all
this water, but it turns out it isn't nearly as big as
what they need."
Most mainstream climate scientists agree that rising
global temperatures are changing precipitation patterns
because of increased evaporation and greater amounts of
moisture in the air. There is greater uncertainty about
how fast climate change is happening and how human
disruption of natural climate cycles will affect day-to-
While sharp political differences remain among interest
groups and elected officials about how critical it is to
respond to climate change, or whether to respond at all,
local planners around the nation are looking ahead and
bracing for the worst.
Chicago, for instance, has developed an "action plan"
that envisions capturing rainfall before it washes into
sewers through small-scale "green infrastructure"
projects. The city also pledged to reduce emissions of
greenhouse gases by making buildings more energy
efficient, using cleaner sources of energy and expanding
"This is an ambitious plan that contains many important
ideas that will ensure Chicago continues to distinguish
itself as an environmental role model for the rest of
the nation," Daley said when he announced the initiative
As with many of the city's other green programs, the
results have been mixed so far, in part because of
The city has repaved 140 alleys with porous pavers or
pervious concrete that allows rainwater to seep into the
ground rather than drain into sewers. Daley also has
pushed for green roofs that help sop up stormwater,
including one atop McCormick Place that returns about 50
million gallons to Lake Michigan every year. But the
projects remain small compared with the scope of the
"Every time the city tears up a street for improvements,
they should be thinking about porous pavement in the
parking lanes and street trees and rain gardens," said
Thomas Cmar, an attorney in the Chicago office of the
Natural Resources Defense Council. "These things don't
require a lot of money upfront but can pay huge
dividends down the line."
Cmar's group recently commissioned a study of Chicago's
sewers by Shaw Environmental, a global consulting firm.
The findings echoed research by the Chicago Department
of Water Management that found more than 40 percent of
the city's sewers fail to handle rainfall greater than
two-thirds of an inch, a worrisome problem that leads to
The analysts also concluded that aggressive use of green
infrastructure, spread out in neighborhoods across the
city, could slow surges of runoff after rainstorms and
make it easier for sewers and the Deep Tunnel to work as
Though top officials at the Water Reclamation District
once resisted many of the proposed solutions, some are
now embracing them.
"Sewer pipes and treatment plants can only do so much,"
said Debra Shore, a member of the district's elected
board. "The alternative is we just live with flooded
basements and polluted waterways, but most people don't
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