What Causes Basements to Flood?  

As our climate has changed in recent years, there is a new kind of storm hitting Chicago with heavy rains that can be very localized, very intense and hard to predict.  They can dump two inches or more hourly on a given neighborhood. Our sewer system was designed decades ago when storm patterns were very different. During intense storms, sewer mains fill up, and additional water pushes into basements through the private sewer drains.

Stormwater is introduced into the sewer system a couple of ways. Catch basins are the grates near curbs that are openings for water to flow down into the sewer mains under the streets. When they become overwhelmed by lots of water in a short time, there may be backup into surrounding basements. 

During a heavy storm, as much as 500 gallons of water can fall on the average residential rooftop.  In the old days, City code required that gutter downspouts be connected to a house's private sewer drain that carries storm and wastewater to sewers.  But when the sewers are full, the water has nowhere to go but your basement.  This is why we recommend disconnecting downspouts from the drainage system and direct the water they carry to your lawn instead. 

The City is working hard to improve our aging infrastructure, but there are 4,400 miles of sewer main in Chicago, and mere replacement is not the answer.  The key is to keep as much water out of the sewer as possible during the heaviest rains. 

If we divert as much water as possible from our sewer system, we will spare ourselves some painful floods.  Nobody can guarantee you will never flood.  

What is the City's Responsibility?

The City can do a few things, including:

• Placing restrictors—known as “Rain Blockers”—in catch basins all over town.  These plastic devices slow down the flow of water from the street.  It goes into the sewer only as the sewer can handle it.  The streets are turned into temporary reservoirs (for 3-4 hours), and it gradually drains.  IF STREETS ARE FLOODED FOR A FEW HOURS, THAT’S GOOD.  IT’S BETTER THAN HAVING IT IN YOUR BASEMENT.  If the restrictors are missing, your sewer will surcharge and push water into your basement. 
• The Department of Water Management maintains sewers in good working order to ensure that they are prepared to handle as much water as possible. We also upsize sewer mains in areas prone to flooding when we are replacing old inefficient mains.

Why Should I Talk to My Neighbors About Flooding Prevention?

All flooding is local.  We are connected by an underground network of open pipes so if we work with our neighbors to lessen the amount of water going into the system, we will have better results.

Much of the water flooding basements is traveling across private property.  Whether it’s your roof gutters or your yard, the City is not allowed to perform work on private property.  It is up to owners to make the appropriate changes to meet the challenges of new weather patterns.     

Do You Have Any Information That I Can Share With My Neighbors?  

• Clean-Up After the Flood

• Managing Stormwater at Home (English)

• Managing Stormwater at Home (Spanish)

• Green Design

• Downspout Disconnection