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Storm Update – September 11 & 12, 2022

09/16/22 01:45:pm

(Milwaukee, WI) – Record rainfall drenched the Milwaukee area on September 11 and 12, 2022, resulting in localized flooding, property damage, and overflows from local and regional sewer systems to reduce the risk of basement backups.

The National Weather Service (NWS) reported 4.78 inches of rain in Milwaukee on September 11, 2022. An additional one to two inches fell on September 12, 2022, raising two-day totals to 5-inches to 7-inches of rain (See map below).

One inch of rain on MMSD’s service area equals 7.1 billion gallons of water

To improve regional wastewater infrastructure and reduce the risk of flooding, the Milwaukee Metropolitan Sewerage District (MMSD) expects to invest more than $2 billion in projects over the next decade.

That includes funding Greenseams® property acquisitions to permanently protect wetlands so they can safely store rainwater and snowmelt, helping reduce the risk of damage from flooding. The program is now safeguarding more than 5,000 acres of land (nearly eight-square miles) in the Milwaukee, Menomonee, Root, and Oak Creek watersheds that can capture and naturally store 2.8 billion gallons of water. The Greenseams® program has planted more than 117,000 native trees and restored about 1,000 acres of land to woodland, prairie, and wetland cover.

MMSD is reporting the following information to the Wisconsin Department of Natural Resources regarding sewer overflows that resulted from heavy rain on Sept. 11 and 12, 2022.


Combined Sewer Overflow: 751 million gallons

Separate Sewer Overflows (SSO): 4.93 million gallons   

  • S. Howell Ave, South of Grange – Wilson Park Creek: 125,000 gallons; duration: 3.25 hours

  • S. 35th & Manitoba – Kinnickinnic River: 1.6 million gallons; duration: 2.68 hours                

  • S. Kinnikinic & St Francis – Lake Michigan: 295,000 gallons; duration: 2.12 hours

  • N. River Rd. & W. Green Tree Rd. – Milwaukee River: 2.9 million gallons; duration: 2.83 hours 

Separate sewer overflows also occurred in local sewer systems in Brookfield, Cudahy, Elm Grove, and Menomonee Falls.       

rain gauge data from 9.12.2022 in milwaukee
mmsd overflow data

MMSD is a regional government agency that provides water reclamation and flood management services for about 1.1 million people in 28 communities in the Greater Milwaukee Area. It serves 411 square miles that cover all, or segments of, six watersheds. MMSD is a regional government agency established by state law.