One year ago, Dane County saw a 15-inch rainfall that flooded streets, homes and businesses, washed out bridges and stranded motorists.
On the anniversary of that flood, Dane County Executive Joe Parisi talked about Dane County’s work to address issues caused by climate change and prepare for what he called “the new reality” of more frequent heavy rainfalls.
At the Aug. 22 Waunakee Rotary meeting, Parisi told the club seven years ago, the county partnered with UW-Madison on modeling to show the local impact of climate change from an emergency preparedness standpoint.
“The modeling that came back was pretty much what we’ve seen in the last couple of years… that the weather is going to be warmer and wetter; we’re going to have both periods of increased intensity of rain events – not just more rain, but more like we’ve seen in the last couple years where we get it all at once,” Parisi said, adding last year was an extreme example.
The county has been seeing two- to five-inch rainfalls that overwhelm its stormwater system.
Debriefing from last year’s flood, county officials have looked at its different stages to learn how best to prepare for the future.
Initially, the downpour caused the most amount of damage; 97 percent of the FEMA damage claims were in Mazomanie, Cross Plains, Shorewood and Middleton. After the initial flash floods, the county saw high water coming through the system.
“All that rain that falls has to go somewhere,” he said, adding that it takes 2 inches of water two weeks to go through the system. Most of the water drained into the Mendota watershed; eventually, it backed up into the Isthmus.
“So we had the initial flash floods, and then we had the back-up,” he said.
A lot of attention has been given to lake levels, but as county officials investigated further, they realized they could not control the levels. Parisi described the lakes as basins connected by drains.
“What we found is that in each one of those channels, the build-up of sediment from mostly urban runoff has just slowed that flow to a trickle,” Parisi said.
County officials have identified a plan to dredge all of the channels, starting with the spot in upper Mud Lake between Monona and Waubesa. They will also dredge the Yahara River between the upper two lakes then at Kegonsa to move the water out. Parisi said the four- to five-phase plan would take place over the next three to four years.
The increase in impervious surfaces as Dane County develops adds to the problem. The county has also invested in keeping more water on the ground by purchasing a 160-acre property in the Town of Springfield adjacent to Pheasant Branch Conservancy near the stream that flows into Lake Mendota. Restoring wetland and prairie there will allow a net gain of 5 million gallons of water to be retained on site during these 100-year rainfalls, Parisi said.
The county will look for similar sites to purchase.
County officials also focused on emergency responses to these large rainfalls, adding airboats, mobile sandbagging machines and pumps.
Along with way, the county has partnered with the agricultural community to reduce phosphorus-laden runoff from entering the lakes and adding algae. These start with basic techniques such as buffer strips between farms and streams to sophisticated manure digesters.
But, Parisi said, county officials found they were not seeing the phosphorus reduction the science had indicated. Discovering decades of sediment within those streams, they embarked on the Suck the Muck program. It was piloted two years ago and started in Dorn Creek last year. In three miles of the creek, tons of sediment were removed.
“The system was choked,” Parisi said, adding the creek was once a spawning ground for pike. Now the water is once again clear.
Parisi showed a video about another initiative at the landfill. This $28 million project is turning methane produced at the landfill and area digesters into renewable natural gas, or compressed natural gas, to be sold on the open market. It not only reduces carbon emissions, but after it is paid off in three years, it will return $7 million to the general fund annually.
The county has created an Office of Energy and Climate Change to assess such projects.
“We’ve realized if we look at the impacts locally of climate change, some of which I just talked about, that we all have to do our part. And there’s a lot you can do on the local level. It’s not just a federal issue or something for people elsewhere to do,” Parisi said.