Winter 2010

Water surrounds a house in Spring Green. The flood was caused by ground- water flooding, instead of the more common surface water flooding. Photo: Madeline Gotkowitz

Water Resources Outreach

Groundwater on the Rise

By Carolyn Rumery Betz

Images of houses tumbling into Lake Delton during record rainfalls in June 2008 remain etched in our memories. The 17 inches of rain that fell over southern Wisconsin in a 10-day period caused catastrophic flooding, and not just from overflowing streambanks.

Another more unusual type of flooding took place at the same time, less than 50 miles away. About 4,300 acres of land located near Spring Green but not in the Wisconsin River floodplain became inundated with water—water that rose from the ground and overtopped the land surface. This was groundwater flooding.

The land remained under water for more than five months. No amount of pumping would reduce the water level because there was no place for it to drain.

“People didn’t understand what was going on because normally water has a place to go,” stated Madeline Gotkowitz, a hydrologist from the Wisconsin Geological and Natural History Survey.

When called into the disaster area, the Federal Emergency Management Agency (FEMA) admitted never having dealt with groundwater flooding, only surface water flooding. Fortunately, Gotkowitz was able to provide the expertise in groundwater hydrology that the agency needed. She concluded the sand and gravel aquifer in the area fills rapidly from runoff coming from areas of fine-grained sediments to the north.

Gotkowitz developed a computer model that showed the groundwater level in the shallow aquifer had risen by as much as 12 feet. The modeling results were supported by real-time measurements from nearby monitoring wells. The monitoring well data suggest that groundwater flooding is likely to occur every 13.5 years in this region.

The town of Spring Green applied for FEMA mitigation grant funds to buy out 28 homes that had sustained damage to more than 50 percent of the structure. Flooding—in this case, groundwater flooding—predicted to occur more frequently than once every 15 years makes a buyout cost-effective and therefore eligible for FEMA funds.

The cost of the buyout is $5.37 million according to Roxanne Gray, hazard mitigation officer for Wisconsin Emergency Management (WEM). The funds are provided through FEMA’s Hazard Mitigation Grant Program. FEMA provides 75 percent of the funds, WEM provides 12.5 percent and, in this instance, a Community Development Block Grant provides the remaining match. The town of Spring Green will purchase and own the land, which will be deed restricted, meaning no development will take place in the future.

“Without Madeline’s scientific expertise in groundwater hydrology, we would never have been able to help the people in the town of Spring Green,” said Gray. “She was the key to our being able to determine where and how frequently groundwater flooding will take place.”

Scientists and policymakers can use real-life extreme weather events like those in Spring Green to help predict where groundwater flooding may occur in other geologically similar areas of the state. Gotkowitz and her colleagues had been awarded a 2009 grant from the Groundwater Coordinating Council to make such assessments. The study, which is ongoing in 2010, will apply a series of climate forecast and hydrologic models to selected landscapes that are vulnerable to water table rise and groundwater flooding.

Communities can use the results of these predictions to develop more environmentally sensitive land use plans. Some communities in Waukesha and Dane counties, for example, may incorporate the information on high groundwater levels into their zoning codes. Areas that are vulnerable to groundwater flooding should not be used for future development.

“It is important to know where groundwater plays a role in flooding,” said Gotkowitz. “I am hoping that communities will be able to use the results of this project to evaluate the need for stricter planning and zoning.”

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