WASHTENAW COUNTY, MI - Nearly five inches of rain fell on some parts of eastern Washtenaw County in just a few hours as storms swept across the area Wednesday night, Aug. 23.
The unusually heavy downpour qualifies as a “500-year” storm for a three-hour time period, meaning such an event has a 0.2% chance of happening at any given time, according to the Washtenaw County Water Resources Commissioner’s Office.
Some areas of the county received between 4.8 and 4.9 inches in roughly three hours, officials said.
“We’ve looked at the tables and charts, and just statistically (it was) a pretty unlikely event,” said Water Resources Commissioner Evan Pratt, who said not every rain gauge has reported, so officials don’t yet have a complete picture.
Just before 8 a.m. Thursday, Aug. 24, the weather station at the Willow Run Airport in the Ypsilanti area reported 5.37 inches of rain in the previous six hours, according to the National Weather Service.
The localized heavy rains seemed to stretch somewhere between Scio Township all the way west to Canton, which experienced significant flooding, with the rainfall also blocking access to a terminal at the Detroit Metro Airport.
Pratt said he’s received reports of deluges from a north-south area stretching from the middle of Salem Township all the way south to Dundee, “a pretty big cell for this type of intense rain,” he said.
In the city of Ypsilanti, municipal crews were busy responding to the storms as early as 4 a.m. on Thursday, said city Department of Public Services Director Bonnie Wessler.
With more rain in the forecast Thursday evening, Pratt’s office is asking residents to report flooding and drainage issues by calling 734-222-6860, emailing drains@washtenaw.org or using the Washtenaw County website.
His staff was busy with triage on Thursday, Pratt said, working with the Washtenaw County Road Commission and other agencies to identify issues, like a washout on the downstream side of the Tyler Dam, near the Willow Run Airport.
Officials also visited areas with a past history of flooding, like Appleridge Street in Ypsilanti Township, where his office earlier this year modified drains to better handle rainfall. “There were not real issues at all with street flooding,” on Thursday following the changes, Pratt said.
“None of the pipes are designed for even the 50-year storm. Pipes are usually a 10-year rain, and the amount you get in a rain like this or even a 100-year rain is a huge amount more,” he said. “No doubt there were some full pipes out there.”
His crews will respond to calls and make sure drains aren’t blocked for as long as it takes after the storm, which can be days, Pratt said.
“Our main goal is to keep the water moving. We want to hear from people who are saying the water is sitting there, and it’s not going down.”
Storms like the ones on Wednesday night are consistent with an increase in weather severity observed in roughly the last 20 years, Pratt said.
“It’s these shorter bursts that are more intense that are emblematic of climate change, and we’ve certainly been seeing that,” he said. “As far as we’re concerned, this is climate-related.”
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