Ken Potter, a UW-Madison hydrologist, likes to imagine the Yahara Lakes around Madison as a clogged bathtub. With little change in elevation between the top and bottom of the lake chain, the stormwater that flows in tends to stay there.

In places built on natural wetlands like Madison, Potter explained that managing runoff is critical to keeping pollutants out of lakes and preventing erosion and neighborhood flooding.

That’s why Potter said he does not understand why the state passed a law earlier this month that limits the amount of stormwater runoff local governments are allowed to regulate.

“The language of the bill was really sneaky,” Potter said. “You should not be allowed to increase the amount of water that leaves the land, because in this watershed, that water goes into the Yahara Lakes.”

And peak flood levels in the Yahara Lakes have been steadily rising, according to the Dane County Land and Water Resources Department. Potter said the increase is due to urban development and increased rainfall caused by climate change.

Historically, most of the runoff from rainstorms and snowmelt would have pooled in the wetland depressions that pocket Madison’s glacial landscape, either evaporating or returning to the water table.

But increasing development means more and more of that water now flows into storm sewers and winds up directly in the lakes, causing their levels to rise during and after storms.

In urban Dane County, current stormwater runoff volume is 150 percent greater than it is in more rural areas, according to a study published by UW-Madison hydrologists last spring.

Currently, developers contain the stormwater their projects displace by directing it into gardens or closed wetlands. Most Wisconsin cities have ordinances that mandate they do so.

But the new act prevents cities from regulating any more than 90 percent of stormwater runoff volume from a location in a year, overriding pre-existing, stricter ordinances in several places, including Middleton.

In Middleton, an earlier policy required developers control 100 percent of their runoff, if they planned to build in areas that drain into wetland basins. City administrators were in the process of expanding the minimum volume control outside of those areas as well.

Volume accounts for water that stays on the land, in addition to the water that flows off of it. Potter explained that the majority of rainfall volume stays on the land anyway, so theoretically, the remaining, unregulated 10 percent runoff volume could be enough to cause flooding.

State Rep. Rob Brooks, R-Saukville and the new floods law’s sponsor, said the act tried to reach a compromise between local regulators and developers who felt they were unfairly targeted by current volume control standards.

“No one was really excited by the final outcome, but I think we reached a good compromise between developers and city regulators,” Brooks said. “We had experts look at the language and we were all comfortable with it.”

Even developers who complied with the old regulatory standards frequently found themselves up against fines after large storms.

“Developers were spending hundreds of thousands of dollars to put in bioretention ponds and meet these standards, and on top of that, they were still getting fined,” Brooks said. “It just wasn’t fair.”

But development in wetlands is exactly what Potter is wary of.

“The biggest issue that has to do with flooding is based on when, where and how we develop — particularly the how,” Potter said. “There is a lot of pressure to develop land, because developing land is an industry and it brings in resources and revenue.”

The new law comes shortly after the state rolled back other regulations protecting wetlands. Both measures were meant to spur economic development across the state, but Potter said he fears they will also create flood hazards, as well as damage prime wildlife habitats.

“From a flooding perspective, the deregulated wetlands are the most important,” Potter said. “The best thing to do is maintain them. They are places where water can be contained, stored and evaporated.”

The problem, Potter said, is that much of Madison’s urban landscape was developed on wetlands.

“In a lot of cases, flooding happens on land that never should have been developed,” he said. “We’re already vulnerable to flooding here. With climate change and land development, we’re going to be even more vulnerable.”

Flooding disproportionately affects people of lower income, as home values are often cheaper on land that exists in historic flood planes.

“Most of the houses on the East side that are prone to flooding are in poor neighborhoods. The entire watershed on the east side of the town was a wetland,” Potter said. “We’ve always seen people of lower income pushed into the flood prone areas, and they are the least equipped to deal with it.”

Experts argue limiting local authority over stormwater could put those communities at greater flood risk, as well as create hazards for places further downstream.

Instead, Potter suggests cities work with developers to design innovative flood water management strategies, such as volume trading, which would allow developers to exchange excess runoff volumes so combined, their net amount of runoff would still meet city standards.

Resources would be better spent re-assessing floodplain zoning, instead of deregulating floodplains, so that developers can accurately assess their risk on a landscape that is being transformed by climate change, Potter recommended.

“But we shouldn’t be doing things that can only result in creating flood risks for other people,” Potter said.

Given Middleton’s specific soil conditions and watersheds, Gary Huth, a Middleton city engineer, said a high level of control is necessary there, to prevent excess runoff and flooding. But he also said the strategies needed to mitigate flooding impacts differ from region to region, which is why local governments should have the flexibility to set their own regulations.

The state’s move to override local regulatory limits opposes the regulatory principles that form the foundation of modern environmental law. In the past, state and federal governments have used their authority to enforce local environmental regulations, not remove them, Huth said.

“What bothers me about that legislation is that it doesn’t recognize that everyone shouldn’t have the same standard,” Huth said. “The hydrologic processes that determine what happens to stormwater vary with location. But Madison and its lakes are especially sensitive to flooding.”