“The intensity of the rain was unusual,” County Board Chairman Kurt Prenzler said. “No one has seen anything like it.”
The storm hit around 3 a.m. Monday, causing severe flash flooding in Chouteau, Nameoki, Granite City and Venice townships. The hardest-hit area was Granite City where streets flooded, cars stalled and residents evacuated their homes after Mother Nature pounded the area with rain for more than five hours.
Prenzler said there were several factors that led to the flash flooding — the actual rain event itself in combination with low-lying areas and inadequate storm drainage.
Jared Maples, a meteorologist with the National Weather Service, said the type of rain event that Madison County experienced is known as “training,” which is a repeated area of rain in a relatively short period. The name training is derived from how a train and its cars travel along a track, without the track moving.
He said weather reports show the thunderstorm moved across the Mississippi River from Spanish Lake through Mitchell and Pontoon Beach.
“They got the heaviest strike,” Maples said.
He said that the southern part of Granite City received abut 4 inches of rain, while the center and northern areas received 5-7 inches.
“There was a deluge of water in a short time and the area couldn’t drain fast enough,” Prenzler said. “It was storm on top of storm.”
He said Pontoon Beach did not experience the flooding issues like it has in years past and Mitchell suffered only minor problems.
Prenzler said the U.S. Army Corps of Engineers turned on the Chouteau Nameoki Venice Drainage District pump around 10:30 a.m. Tuesday, which began to relieve the flooded areas near I-270 and Illinois 3 and around Mitchell. He said all other pumps were running and doing what they were intended to do.
“Water was draining into Horseshoe Lake,” he said.
Prior to the storm, the lake was a foot below its normal level of 404 feet. By Tuesday, Horseshoe Lake was at 405.4 feet.
“The past couple of years, Metro East Sanitary District worked to make improvements in the system,” Prenzler said. “The level of Horseshoe Lake was lowered to increase water storage capacity and the ditches and canals were cleaned out to improve the flow of storm water.”
Prenzler said drainage issues have been a problem in the area for decades. This spring, he lobbied local legislators asking for funding of stormwater and drainage projects to be placed in the capital bill.
“To date these projects have not been funded,” he said. “This weather event shows just how much they are needed.”