The extreme winter weather across much of the northern United States is increasing spring flood risks in some areas, a situation risk engineering experts warn should be taken seriously by those in potentially affected states and municipalities even if they haven't previously experienced flooding.
A combination of large amounts of snow and deeply frozen ground is elevating the potential for spring flooding, including rivers in highly populated regions, putting many people and businesses at risk.
“Spring floods are real,” said Gregory Lanshe, assistant vice president and director of risk engineering, North American property at Zurich Insurance Group Ltd. in Schaumburg, Ill. “So when we experience a winter like we've gone through there is a higher risk.”
In a March 20 spring outlook, the National Weather Service said, “An unusually cold and wet winter across the Upper Mississippi Basin, Great Lakes region, Ohio River Valley, northern Middle Atlantic, New York and New England has produced an above-normal amount of water in the current snowpack and a deep layer of frozen ground much further south than typical.”
Given the frozen ground in those areas, “the flood risk is highly dependent on the amount of future rainfall and the rate of snowmelt this spring,” the National Weather Service report said.
“We're all going to learn some new lessons this spring season because the rainy season is coming, and we still have snow,” said Marilyn L. Rivers, director of risk and safety for Saratoga Springs, N.Y. “Here in the Adirondacks some areas still have 30 inches of ice.”
Among the areas highlighted in the National Weather Service outlook as being at risk of exceeding moderate flooding depending on future rainfall and rate of snowmelt are sections of the Upper Mississippi and Great Lakes regions.
Meanwhile, the Northern Middle Atlantic, New York and New England regions are among those facing a risk of exceeding minor flooding, primarily because of snowmelt and expected spring rain.
“In addition, significant river ice increases the risk of flooding related to ice jams and ice jam break-ups,” according to the outlook. “While there are no widespread areas with risk of exceeding major flooding, a deep layer of frozen ground and significant river ice throughout the northern tier of the United States may cause localized major flooding.”
“We're all trying to do some risk mitigation efforts,” Ms. Rivers said. Among other things, she said, public sector risk managers in areas at risk of spring flooding are examining dams and looking for floating debris such as fallen trees that might block rivers and streams or damage dams. “Those trees could become barriers to rivers or dams in addition to the huge blocks of ice. So it's almost like a grocery store of debris that's coming.”
And sheets of ice floating down rivers have the capacity to damage bridges and river locks, the Saratoga Springs risk manager said. “Those ice floes really have to be watched because they can be devastating,” she said. “When a bridge is taken out, that can be the main thoroughfare for a community.”
In many regions, “The real issue is the fact that the ground is frozen,” said Ronnie Gibson, vice president and chief engineer at FM Global in Johnston, R.I. “It's like it's melting on concrete, and that's what causes the issue.”
“We also are concerned with surface water runoff,” Zurich's Mr. Lanshe said. “Water sitting on the surface that can't be absorbed will run until it finds someplace to enter.”
Such runoff situations might affect businesses that hadn't considered themselves at risk of flooding, Mr. Lanshe said. “We may have businesses that are not in a flood zone that when there's a spring rain, frozen ground — that water might run off and enter your building,” he said.
In Illinois, “It's a situation that we are monitoring very closely and we will throughout the spring,” said a spokeswoman for the Illinois Emergency Management Agency. “At this point we don't see any real hot spots,” she said, adding that the flood situation can change quickly.
“We are in close contact with the National Weather Service ... and also the Illinois Department of Natural Resources,” the spokeswoman said.
“When we do start to see ramping up toward flooding, what we like to do is get out and meet with local officials in the region,” she said. In such situations, the Illinois agency seeks to determine the local agencies' preparedness, advise them of assistance the state can provide and, if necessary, stage flood-fighting materials such as sandbags in the area.
“We've experienced several times — including last year — where a rain event completely changed the outlook and we were in a flood fight,” the spokeswoman said.
A spokeswoman for Iowa Homeland Security & Emergency Management said her agency also is remaining vigilant preparing for developing flood conditions and staying in contact with its county coordinators. “We have a very close relationship with the National Weather Service offices in our area,” she said. “We depend on them very heavily.”
Mark Fuchs, service hydrologist in the St. Louis forecast office of the National Weather Service, suggested the level of flood risk varies considerably by region, and that the area his office covers — eastern Missouri and west central and central Illinois, including sections of the Mississippi and Illinois rivers — is currently experiencing flood risk levels at or even slightly below seasonal average, after those levels were elevated only a few weeks ago.
The risk profile in his area has recently changed, Mr. Fuchs said, because of the way the snowpack has melted in some areas of Wisconsin and Minnesota.
“That risk has gone down because we've lost a fair amount of snow cover and fortunately that melting occurred gradually rather than all at once,” he said. “We're getting more and more into a situation where rain becomes the driving (flood) mechanism, not any snowmelt.”
There are areas elsewhere, however, where the flood risk due to snowpack and ground freeze may remain elevated, Mr. Fuchs said.
Both Mr. Lanshe and Mr. Gibson stressed that flood risk can be mitigated.
“It's pretty basic stuff that you can apply,” Mr. Gibson said, citing businesses raising or moving equipment or stock or taking steps to waterproof facilities or installing flood protection features such as floodgates or walls to protect properties. “These don't have to be complex plans.”
“It begins with understanding the exposure,” Mr. Lanshe said. “You've got to think about where water may enter your building. All of a sudden you realize that you are in the path of water. You didn't expect it but there it is. Be prepared.”