A year after historic rains wreaked havoc on Dane County, some residents continue to feel the impact from high groundwater that’s being blamed for millions of dollars of additional damage.
Almost one out of every 10 acres of cropland in the county went unplanted this year, according to U.S. Department of Agriculture statistics, and county officials say they’ve had reports of waterlogged basements.
County officials say years of excessive precipitation — including the 11 to 15 inches of rain that fell on parts of the county on Aug. 20, 2018 — have left the groundwater tables so high that the soil can’t drain, making low-lying areas prone to flooding.
Last year was the second-wettest year in Madison out of 149 years of modern record keeping, according to the National Weather Service.
Three of the four preceding years saw above-average rainfall.
John Reimer, assistant director of the Dane County Land and Water Resources Department, said this year’s above-average rainfall is also contributing.
“The water table isn’t very deep to begin with,” said Jean Bahr, a professor of geology and geophysics at UW-Madison. “It doesn’t have to go up very much before you start having trouble.”
David Hart, a hydrogeologist with the Wisconsin Geological and Natural History Survey, said much of the county’s land was originally wetland, which implies a shallow water table.
“We’ve engineered a lot of our landscape to keep water off of it,” Hart said. “A lot of our landscape wanted to be wet, and was wet in the past. Several wet years in a row, that water table comes up … and causes these issues.”
Dane County Executive Joe Parisi said the nearly 50 square miles of unplanted cropland will cost farmers millions of dollars.
The county’s emergency management and planning departments are evaluating the flooding risk for homes that may not fall within federally designated floodplains but could be susceptible to water damage in extreme rain events, which are happening more frequently than in the past.
“They may think the problem is lakes or rivers but actually it’s the water in the ground coming up because it has no place left to go,” Emergency Management Director Charles Tubbs said in a statement. “That’s why we’re encouraging all homeowners to look into flood insurance policies and consider other household preparations — like not storing sensitive documents downstairs — in the event water starts coming in.”
The analysis of damage reports, topography and soil types will be used to identify areas most likely to be affected by both runoff and elevated groundwater levels in order to warn homeowners and landowners of previously unknown risks.
The study is part of the county’s $23.8 million in flood mitigation efforts undertaken after last year’s rains caused an estimated $154 million in damages.
Federal emergency aid for Dane County totaled just $5.6 million, including $3.8 million in grants for some 929 individuals and $1.8 million to help rebuild roads and bridges.