Ice jam causing minor to moderate flooding along Illinois, Sangamon rivers

Portions of the Sangamon and Illinois rivers are currently under a flood warning due to ice jams that have caused flooding in some parts of west central Illinois.

The National Weather Service in Lincoln said that the Sangamon River at Oakford in Menard County and Chandlerville in Cass County and the Illinois River at Beardstown in Cass County and Havana in Mason County have seen at least minor flooding in some areas, with minor to moderate flooding in the forecast for the next several days.

In Oakford, NWS says that the observed stage Friday afternoon came in at 471.4 feet and will crest sometime early Sunday morning at 473 feet, causing flooding in low-lying agricultural areas. Chandlerville had an observed stage at 458.7 feet, with NWS forecasting that the stage will go up to 460 feet by Sunday morning.

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Impacts along the Illinois River are expected to be delayed, with Beardstown expected to increase to 20.5 feet by next Friday, which could lead to seepage problems in the South Beardstown Drainage and Levee District. The observed stage at Havana is expected to increase to 19.5 feet on Friday, which would lead to the closure of an access road to the north campground at Anderson Lake.

The rise in water levels is due to ice jams situated along parts of the river. Nicole Albano, a meteorologist with NWS, said that these ice jams have come about as a result of three major weather events over the course of the past month: frigid temperatures last week – which created ice along rivers and streams across central Illinois; the snowfall that followed it; and a warm-up this week that has dumped large amounts of rain in the area.

“Because the ground is frozen, all of that snowmelt and rainfall that is occurring is pure runoff, which then makes its way into our rivers and streams,” Albano said. “With any of the increases or higher flows, it’s a combination of runoff from snowmelt (and) some heavier rain from this past week.”

With the cold temperatures followed by warmer conditions combined with the frozen ground and runoff, Albano said that ice can build up along these rivers and streams, leading to the jams. The blockage can increase the likelihood of flooding, with levels quickly increasing once the ice gets stuck.

“If an ice jam is stuck, your water is going to rise pretty rapidly behind it, which is what happened in Oakford yesterday and continuing into this morning,” Albano said.

Albano said that most of the flooding is in those low-lying agricultural areas and has yet to spread into residential or commercial areas. But as it continues to move towards Chandlerville downstream, the jam could grow and create conditions that may lead to bigger impacts down the line.

“It can lead to future rises and fluctuations at the river,” Albano said.

Predicting when all of this will abate is a difficult task, with Albano saying that water levels have been rising quicker than anticipated. That means the crest levels could be higher than previously thought, matching up firmly with the idea that those levels are hard to judge.

“Ice jams are really hard to forecast when they’re going to crest,” Albano said. “You don’t know when they’re going to be in place, if they will break free, or if they will hold up and cause significant flooding.”

Simply put, Albano said that once the ice melts off, the threat of flooding will end, although it may be a while still with ice still present along both rivers.

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“Temperatures are going to be warmer than normal these next several days to close out the month of January into the start of February, which is good because we’ll be able to melt any ice that is on our area rivers,” Albano said. “Near-term forecasting of it is very difficult to do.”

Albano recommends that anyone who encounters an ice jam report it to local law enforcement and if they see any flooding, that they move to higher ground.

“Rises associated with ice jams can be on the matter of one to several feet per hour,” Albano said.