City Engineers Propose Storm Water Changes

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Madison’s engineering division is drafting revisions to a city ordinance to help combat flooding. The changes would require better storm water practices for both development and redevelopment projects.

The city’s proposed changes are aimed at avoiding the historic flooding experienced by the east and west sides of Madison in summer 2018, when elevated lake levels flooding low lying areas of the isthmus and flash flooding devastated communities in Shorewood Hills.

The ordinance change would require new standards for developers. New development would require elevating structures and larger culverts. It would also require dedicated lots for diverting water to ponds and green ways.

Those looking to redevelop would need to plan to absorb about half an inch of rain with green infrastructure. That includes using things like rain gardens or permeable pavement.

Hannah Mohelnitzky is a spokesperson for the City Engineering office. She says the proposed changes will beef up land use requirements for developers.

“Basically, there is an increase in requirements when it comes to keeping water on the land [and] that’s something that we’ve never done before,” Mohelnitzky says.

“So, say someone wants to build. We want to make sure they have the infrastructure in place and there’s plenty of land also for new development that can keep the water controlled and so it’s not flowing uncontrolled to other areas impacting other people. That’s really important. It may require more land, and more land may mean more money for people to have to purchase to be able to support that infrastructure, but in the end…it will really help our community.”

An online presentation from city engineers Greg Fries and Janet Schmidt show that the flooding has hit low and enclosed areas and historic wetlands the hardest

The changes come as the city also predicts more significant rain events in the future. The same presentation from city engineers shows a fifteen percent increase in precipitation over the last seventy years.

The proposed changes require developers to account for these larger weather events, and their impact on the storm sewer system. The city wants to expand the capacity of the storm sewer system to accommodate a 200-year flood event, which is six to ten inches in a 24-hour period.

“The storm water infrastructure needs to be able to detain the 1, 2, 5, 10, and 100 year storm events, but the new change is adding a 200-year storm event that involves post-development peaks. , but they must put in the storm because we’re getting that 100-year storm event more frequently, which is what Mother Nature is throwing us,” says Mohelnitzky.

The ordinance revisions come as the city and county implement other practices to mitigate flooding. A plan to dredge the Yahara River and improve water flow from Lake Monona to Lake Waubesa is slated to begin in spring. The city also plans to make structural changes to the Tenney Locks, which regulate lake levels.

The city is seeking public comment on the ordinance changes, from both citizens and developers, until April 10. Public input meetings are planned for late February and early March, and more information is available here. You can also email input to [e-mail].

Picture Credit: Inge Maria on Unsplash

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