Torrential rains cause sewer overflow, flooding

A single combined sanitary and storm sewer near N. 35th St. and W. Congress St. briefly overflowed Tuesday afternoon into Lincoln Creek, Milwaukee Metropolitan Sewerage District officials said.

The first combined sewer overflow of this year lasted only 10 minutes, from 1:10 p.m. to 1:20 p.m., said Sharon Mertens, MMSD director of water quality protection.

Torrential rains falling at a rate of more than 3.5 inches an hour at that time overwhelmed the capacity of a municipal combined sewer and caused the overflow, according to Mertens. Sewer overflows reduce the risk of sewage backups into basements.

MMSD will review flow records at the sewer outfall before releasing an estimate of the overflow volume. The volume must be reported to the state Department of Natural Resources within five days.

Tuesday's overflow was the first since April 2015, records show.

Rapidly filling rain gauges prompted the National Weather Service to issue a flash flood warning for Milwaukee County Tuesday afternoon.

The alert warned of flooding of streets and small streams across the Milwaukee metropolitan area Tuesday afternoon with storms dropping an additional one to two inches of rain between 2 and 3:30 p.m. The warning ended at 3:30 p.m.

The weather service advised motorists to use caution driving in flooded streets or underpasses beneath bridges.

The Milwaukee Department of Public Works crews responded to 41 reports of street flooding by 4 p.m. Tuesday, officials said.

A series of thunderstorms poured more than 2.6 inches of rain on the south side of Milwaukee by 2:30 p.m. Tuesday, according to an MMSD rain gauge in the 200 block of W. Lincoln Ave. A gauge in the 6000 block of S. 13th St. recorded nearly 2.5 inches by 2:30 p.m.

Shorewood received more than 1.5 inches of rain by 2 p.m.