The August 2025 Storms: MMSD’s Role in Managing Flooding and Protecting Our Community

Although the August 2025 storms caused widespread flooding across the region, decades of flood management investments helped protect many neighborhoods from even greater damage. 

Since 2000, approximately 200 homes that were once located in the 1% probability floodplain are now outside of it. Without those flood management projects, many more families would likely have been affected by flooding. 

The 1%-probability floodplain is commonly referred to as the 100-year floodplain. “100-year flood events” have a one-percent chance of occurring every year. MMSD designs and builds infrastructure to handle storms up to the 100-year flood level. Larger storms have occurred and will occur, such as the 1,000-year rainfall in Milwaukee in August 2025. 

The Milwaukee County Grounds Flood Management project was designed to hold 315 million gallons of water. During the August 2025 storms, the facility performed as designed, holding millions of gallons of water, helping reduce downstream flooding in the Menomonee Valley and downtown Milwaukee. 

Under normal conditions, the area functions as public green space. During major storms like this one, it plays a critical role by temporarily storing floodwater and helping protect nearby neighborhoods. 

By storing and draining water into the ground naturally, Greenseams® helps prevent future flooding and water pollution while supporting and protecting MMSD's structural flood management projects - infrastructure investments worth hundreds of millions of dollars. Through the Greenseams® program, MMSD permanently protects land with highly absorbent soils that naturally soak up rainfall and slow runoff before it reaches streams and rivers.  

The Babiasz Greenseams® property, in the Menomonee River Watershed, includes 101 acres of protected land. During the August storms, this land helped store and absorb rainfall, reducing runoff and helping manage flooding for nearby communities. 

During the storms Hart Park flooded, which was exactly what it was built to do. In 2007, Hart Park was expanded from 20 to 50 acres, creating space for floodwater to temporarily spread out during large storms. The project also included levees designed to protect nearby neighborhoods from river flooding. 

As part of the project, 58 homes were purchased and removed from the floodplain. During the August storms, these homes would likely have been flooded if they had still been in the floodplain.

In 2020, MMSD partnered with Milwaukee County Parks and other partners to restore a section of the Kinnickinnic River through Pulaski Park. 

The project removed more than 1,700 feet of aging concrete river channel and restored the river to a more natural shape. This allows the river to slow down, and spread out safely during high flows, which was seen in the August 2025 storms. 

Honey Creek on the Menomonee River, downstream of the Blue Mound Road bridge, sustained significant damage. Approximately 150 feet of concrete channel panels were displaced, with each panel weighing about 21,000 pounds — totaling roughly 270 tons of concrete moved by floodwaters.  

An Emergency Declaration was issued so MMSD could quickly stabilize and repair the damaged areas. 

Looking ahead, MMSD and partners plan to replace sections of the concrete channel with a more natural stream design that slows water during storms, improves neighborhood safety, and enhances habitat for fish and wildlife. 

Despite being cleared before the storms, a trash rack at McCarty Park in West Allis, near an underground conveyance system, accumulated debris rapidly during the storms. Water overtopped the structure, flowing across nearby roadways, and basements downstream were flooded. 

An Emergency Declaration was issued to address the problem. The expedited project aims to reduce blockage at the trash rack, ensuring stormwater can flow into the culverts and helping prevent future flooding in the surrounding neighborhood.  

During the August 2025 storms, flooding occurred on top of two diversion structures that send sewage from the Metropolitan Interceptor Sewer into the Northwest Side Relief Sewer, allowing the Menomonee River to enter the Northwest Side Relief Sewer Tunnel. This amount of water blew off the lid of the tunnel, which has 4 pieces, each weighing 50,000 lbs. In addition, transformers, electrical systems, and gate machinery were damaged in this area.