Flood potential

 

Flood potential slightly above normal in Wisconsin

It’s been a long, cold winter and everyone is looking forward to spring. The upcoming spring thaw, however, has many people thinking about how high area rivers might get. 

Predicting the potential for spring floods can be tricky and takes into account numerous factors. According to the hydrologic outlook issued by the La Crosse Office of the National Weather Service on March 6, the flood potential across Wisconsin is a little above normal. For Northeast Iowa, the potential is near normal. 

The hydrologic outlook states, “One item of concern moving forward into spring is the deep frost across the region. Even as the snow melts and runs off, the frost will take some time before it is completely out of the soil. Therefore the risk for enhanced runoff from spring rainfall will be higher, and thus we may see an increased risk of flooding from rainfall later this spring.  

“Another concern is with the amount and thickness of ice in area creeks and rivers. The prolonged and deep cold has allowed for widespread formation of ice, and the ice is thicker than normal. As this ice breaks up, ice jams are a definite possibility, especially in typical areas such as near bridges and other constrictions in the river or where the river makes sharp turns or meanders. Large chunks of ice moving downstream could get hung up in these areas and lead to jams and potential flooding.

“So, it is safe to say that any flooding we eventually see in the coming weeks will depend greatly on future weather conditions. This includes the rate at which the snow melts and any future rain events. And of course, we could still see some additional snow events in the coming weeks that could alter the spring flood potential.”

The river stage for the Mississippi River at McGregor was 8 feet as of March 10. According to National Weather Service charts and the hydrologic outlook, there is an 84 percent chance that the river will exceed the flood stage of 16 feet sometime between March 10 and June 8. There is only a 24 percent chance that the river will exceed 20 feet. There is a just a 10 percent chance of exceeding 23 feet, based upon current conditions. Sixteen feet is the flood stage at McGregor. Sixteen to 20 feet is considered minor flooding. Twenty feet to 23 feet is moderate flooding. Above 23 feet is considered major flooding.

Flood stage for the Kickapoo River at Steuben is 12 feet. Minor flooding is 12-13 feet. Moderate flooding is 13-15 feet. Major flooding is above 15 feet. As of March 10 the river stage at Steuben was 6.86 feet. According to the National Weather Service, there is a 73 percent chance of minor flooding sometime between March 10 and June 8. There is a 20 percent chance of moderate flooding and there is less than a 5 percent chance of major flooding, based upon current conditions.

As of March 10, the river stage for the Turkey River at Elkader was 5.03 feet. Minor flooding is 12-16 feet. Moderate flooding is 16-20 feet. Major flooding is over 20 feet. There is a 46 percent chance of minor flooding this spring. There is a 12 percent chance of moderate flooding and less than a 5 percent chance of major flooding, based upon current conditions.

As of March 10, there was a river stage of 3.99 feet for the Wisconsin River at Muscoda. Nine to 10 feet is minor flooding, 10-11 feet is moderate flooding, and above 11 feet is major flooding. There is a 50 percent chance of minor flooding, a 25 percent chance of moderate flooding and a 10 percent chance of major flooding this coming spring based upon current conditions.  

As far as climate information is concerned, the hydrological outlook says, “Looking ahead to the spring of 2014, climate models continue to suggest that temperatures will remain below normal. This will likely delay the snow melt across the region. Meanwhile a general flow of northwest winds aloft will likely result in near to below normal precipitation into March.

“The flood potential analysis is based on current soil and snow conditions combined with a broad spectrum of potential spring weather conditions reflected in the climate record from 1949 to 2012. 

“The Upper Mississippi River watershed was generally characterized by normal to below normal soil moisture conditions going into the December freeze-up. Winter precipitation has been above normal across Central Minnesota and Northwest Wisconsin with near normal precipitation observed across the rest of our region. Snow cover is present across the entire watershed, with snow water amounts ranging between 2 and 3 inches across southern parts of Minnesota and Wisconsin, as well as Northeast Iowa. Amounts of 3 to nearly 4 inches are seen over parts of North Central and Western Wisconsin, with 5 inches of snow water content in the upper portions of the St. Croix, Chippewa, and Wisconsin River basins.

“Due to the persistent cold temperatures across the Midwest this winter, the ground has frozen down to 2-3 feet across Northeast Iowa and 3-4 feet across Southeast Minnesota into Southwest Wisconsin. Frost depth as low as 5 feet has been reported for portions of Central and North Central Wisconsin.

“As a result of these conditions, there is a somewhat elevated risk of spring flooding across much of Wisconsin, including the Black, Trempealeau, Kickapoo, and Wisconsin River basins. The risk is normal or perhaps slightly below normal further to the south and west including the Northeast Iowa basins such as the Cedar, Upper Iowa, and Turkey rivers. 

“For Southeast Minnesota rivers and the mainstem Mississippi River, there is a climatologically normal risk of minor flooding with a diminished risk for moderate or higher level flooding.”

Rate this article: 
No votes yet