In August of 2018, the chain of lakes connected by the Yahara River had remained above target summer maximum levels—the appropriate lake levels set by the Wisconsin Department of Natural Resources—for four months, despite efforts to eliminate blockages in the system. Heavy rainfall on August 21 threatened to push the lakes over the edge. The city of Madison closed major thoroughfares as the water rushed in, damaging homes, businesses, and public infrastructure. First responders worked all night, evacuating residents from flooded homes and rescuing stranded motorists. In the aftermath of the flooding, there was one casualty and an estimated $209 million in damages— the majority of which was not covered by insurance. While the cause of the flooding is an environmental quagmire, it boils down to this: inefficient movement of water through the Yahara Watershed and torrential rainfalls were the impetus for the catastrophe.
The Yahara Watershed does not naturally lend itself to a fast flow. The river drops a mere 1.5 feet over four miles; it’s flat, so the water moves slowly. However, several other factors exacerbate the slow movement of water, including aquatic plants, sediment, and debris. A task force on flood mitigation was created after the 2018 flooding to pose solutions for these flow restrictors, with input from the public. Flood mitigation efforts were ongoing before the flooding, and the Dane County Land and Water Resources Department (LWRD) has amped up its efforts since, at the recommendation of the task force.
Aquatic plants, a main area of focus, hinder the movement of water because of friction between the plants and water. They can also impede public access to beaches and support toxic algae growth by releasing phosphorus during decomposition. Additionally, invasive aquatic plants compete with native plants for sunlight and nutrients, which disrupts the ecosystem. In 2018, Dane County aquatic plant harvesters cleared away 8,496 tons of plants, approximately one-third of which was removed to alleviate flow restrictions. After the flooding in late August, aquatic plant harvesters managed to double the rate of water leaving the Yahara Watershed.
The 2019 budget saw an increase of over 53% devoted to lake plant management from the previous year, bringing the total up to $773,400. The added funds went toward hiring more employees and purchasing new equipment, including two plant harvesters. “These aquatic plant harvesters will help advance our efforts to mitigate flooding due to climate change rains and more quickly move water through the Chain of Lakes system,” said Dane County Executive Joe Parisi. The extracted nutrient-rich plants are turned into compost, which residents can reclaim at the county compost site. For those interested in tracking the plant harvesters or obtaining compost, please visit the LWRD website.
Debris and sediment buildup are other factors that slow the flow of water through the Yahara Watershed. Friction between debris and water hinders the movement of water. In July 2018, 31 dump truck loads of debris were removed from a river bed in Stoughton, and the flow increased by 20%. Sediment accumulation is a natural process that has accelerated at an unnatural pace because of runoff from erosion caused by urban development. Urban runoff deposits approximately 8.5 million pounds of sediment in the Yahara Watershed each year. The sediment buildup raises riverbeds, leading to a decrease in water storage during floods, slower movement of water through the system, and damage to fisheries.
While Dane County began the “Suck the Muck” project in 2017 to remove legacy sediment from streambeds, this initiative was mainly aimed at controlling algae growth fueled by nutrient-rich sediment, rather than flood control. In 2019, Dane County announced an extensive five-phase project to dredge six sites on the Yahara River, which will take place over four years. The project aims to cut in half the amount of time it takes for water to travel through the Yahara Watershed. The first phase began early this summer and targets the stretch of river between Lake Monona and Lake Waubesa. The $2 million initiative will remove two to three feet of sediment from an area 50 feet wide, stretching one and a half miles.
Efforts to improve the flow of water through the Yahara Watershed have been promising, but the flooding issue goes beyond the shorelines. In 2018, soil and wetlands, two other rainwater storages, were overwhelmed as well— because both are dwindling as development expands. Development in the Yahara Watershed has doubled since 1970. Urban development increases the presence of impervious surfaces, including parking lots and roads. These surfaces prevent rainwater from soaking into the ground and create surface water runoff instead, which enters the lakes, “increasing the risk of lake and stream flooding”, stated Ken Potter, Emeritus Professor of Civil & Environmental Engineering at the University of Wisconsin.
Wetland loss in the Yahara watershed has increased flooding risks as well, with an estimated 56% of the original coverage lost. This is devastating for the ecosystem, because wetlands provide a myriad services, including rainwater storage, filtration of water entering the lakes, protection of shorelines from erosion, and a habitat for native flora and fauna. Protecting wetlands is a crucial step not only for flood prevention, but also the health of the ecosystem as a whole. Earlier this year, Dane County purchased 79 acres of land in Middleton for $4 million for the purpose of wetland restoration. The added flood water storage will prevent about 5.9 million gallons of water from going downstream, according to Parisi.
Dane County has made significant strides in flood mitigation, but individuals can make an impact as well. For instance, the city of Madison is encouraging homeowners to install rain collecting features, such as rain gardens and porous pavement, by offering to reimburse 80% of the costs up to $1000. These green infrastructures keep water out of the storm drains, reducing runoff, which helps decrease flooding risks. During the fall, residents can help curtail the growth of aquatic plants and toxic algae by raking up phosphorus-rich leaves to prevent them from entering the streets and storm drains. It’s also important to stop littering, as trash can build up in the rivers or storm drains, which prevents the water from flowing quickly. Clogged storm drains lead to localized urban flooding during heavy rain events, so it’s essential to keep them clean.
What happened in Madison two years ago is not an isolated event; heavy downpours have been intensifying across the United States, and the Midwest is one of the hardest-hit areas. In a world where climate change has made extreme weather events increasingly common, we must take every measure to ameliorate the environmental damage to our lakes, rivers, and wetlands, which will, in turn, increase flood protection.
The 2018 flooding was the consequence of environmental damage, but the initiatives taken since— by Dane County officials and residents alike— have shown crucial steps toward a healthier and safer future.
[Sources: Dane County LWRD; Simpson Street Free Press; Wisconsin State Journal; National Climate Assessment]