Committee mulls water levels in west Wilmette

The engineers studying west Wilmette’s storm sewers now know the minimum protections Wilmette wants built in to an upgraded storm sewer system west of Ridge Road, after meeting Monday with the village’s municipal services committee.

Members of the committee agreed with Engineering Director Brigitte Berger that an improved system should be able to handle the kind of storm Wilmette has a 10 percent chance of getting in any given year; in other words, a so-called 10-year storm.

But that will come with some residential inconveniences, they agreed.

Committee members decided that an acceptable flood control system could still allow temporary standing water in the streets, as long as it didn’t top six inches (the standard curb height), didn’t go past right-of-way limits past the curbs, and did leave roads and intersections passable by police, fire and ambulance vehicles.

Whatever system is devised should also provide homes full protection from overland flooding, they agreed.

The guidelines they told Thomas Burke, of Christopher B. Burke Engineering, to adhere to are strictly baseline, committee members said, as an audience of between 25 and 30 west Wilmette residents listened.

“I know there are going to be a lot of point solutions for specific areas,” Trustee Cameron Krueger said.

Trustee Alan Swanson and committee chair Julie Wolf agreed, but Wolf said she was pleased with the amount of progress

Burke’s company has been gathering and studying several types of data – physical system testing, resident surveys, and records research among them – about west Wilmette’s aging separate sewer system since February.

Once the team has reviewed the system and identified its weaknesses, such as areas where storm water tends to bottle up in narrow pipes and wind up on lawns and streets, it can devise ways to help minimize those weaknesses. However, his team still couldn’t go forward to design upgrades until it knows what Wilmette officials consider minimum protection levels and maximum flooding allowances.

With those in hand, Burke said, his company can complete its analysis and provide recommendations sometime in November. Once the village board has those recommendations, it can decide how to tackle the upgrade program.

Trustees mulling the minimum requirements heard from Berger that setting the baseline at a 10-year storm level is today’s standard when new subdivisions are developed.

She also laid out the number of times the village has experienced extremely heavy storms over the past 34 years.

There have been four 100-year storms, storms that the village has a one percent chance of getting in any year, since 1980, the latest in 2001, she said; Wilmette experienced a 70-year storm in 2008 and a 50-year storm in 2002.

Between 2011 and the end of last year, the village experienced storms in which one or both of Wilmette’s measuring stations confirmed precipitation amounting to five to 25-year storm levels, Berger said.

“Are these rain event measurements ever recalibrated?” Swanson asked Burke.

Rain event standards were first calibrated in the 1960s and recalibrated in the 1980s, Burke replied. The engineering community is now looking at revising them yet again, he said, and his company has already done work of that kind on its own.

“That’s important to note because we’re aware there is climate change, and that makes the situation even more volatile,” Wolf said.

WET AND DRY WHAT: flood control WHERE: west Wilmette PONDERED BY: village municipal services committee MINIMUM PROTECTION: 10 year storm

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