City officials say increasing rainfall levels caused by climate change mean Evanston needs to spend roughly $500,000 over the next two year to study how stormwater flows through the city.

Public Works Director Dave Stoneback said the study would develop a hydrologic and hydraulic model for the city, to determine how water flows over land and through the city’s sewer system.

Once the city has sufficient data to assess the potential risks from future storms, Stoneback says, it may need to develop a new stormwater charge that would be added to water bills, to fund programs to respond to the risks.

The charge, he suggested, might be based on the impervious surface area of each property.

Stoneback noted that after a big storm in 1987 that left many basements flooded with three to five feet of sewer water, the city committed to upgrade its sewer system at a cost that ended up totalling $210 million. That projecthas dramatically reduced flooding problems in the city.

But he told the city’s Transportation and Parking Committee Wednesday night thatclimate change is leading to higher intensity storms that drop much more rain in shorter periods of time, raising questions about whether the investment made in decades past to prevent flooding will prove sufficient into the future.

He said that green infrastructure projects can help in some sections of the city — where the soil is sandy — but that they’re not economically viable in many other parts of the city where clay soil makes it difficult for water to infiltrate quickly into the ground. And, he said, projects like permeable paving require added spending for maintenance to keep them working properly

He said city staff has developed a Stormwater Management Guide, which will be submitted for City Council approval in December and at that time aldermen will also be asked to authorizing hiring a consultant to conduct the stormwater study.

Bill Smith is the editor and publisher of Evanston Now.

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