Heavy Rains Cause Chicago Area Flooding

 

Heavy rains swept through the Chicago area Wednesday morning challenging commuters and the engineers at the Metropolitan Water Reclamation District. Flooded viaducts contributed to major traffic woes Wednesday morning as 2.5 inches of rain fell within an hour in the northern Chicago area. The Edens expressway was shut down at 7:00 am after viaduct flooding on Pratt Avenue. It took a little more than three hours before the expressway was reopened.

As the rain came down, engineers at the Metropolitan Water Reclamation District had their eyes glued on their computer screens. The district controls 76 miles of waterways stretching from the Wilmette locks to the dam at Lockport. When rain is forecast, the district first lowers the water levels in the system. That happened at 1:00 am.

“We increased the flow in the waterways by opening gates at Lockport, so we have nine pit gates. They are essentially gates that allow flow through the dam to pass through so we increased the flow in the waterways by opening those nine pit gates,” said Edward Staudecher of the MWRD.

The engineers essentially pull the plug on the waterway system when they open the gates beneath the Lockport dam. Normally, water flows through Lockport at 2,000 cubic feet per second. At 1:00 am, engineers increased the flow to 5,000 cfs.

Lawrence Mazzocco arrived at the control center at 6:00 am. With a new, more severe rain forecast at that time, it was time to take more action.

“We had to act aggressively to get more water out of the system as quick as possible. At that point, I think we went to like a 14,500 flow at Lockport, 14,500 cfs,” he said.

With the water down nearly a foot in the system, Mazzocco had to worry about a new problem: not enough water for navigation.

“We were below minus 4 at Sag junction, and minus 4 is virtually our bottom. We probably had all barge traffic stopped at that point,” he said.

The water levels in the system were dropping but the deep tunnel was filling up fast.

“At 8:20, the deep tunnel was at 4 percent. By 9:20, 9:30, it was at 99 percent,” he said.

The North Branch was rising quickly but the bigger worry was the North Shore channel from Wilmette. If the North Shore Channel got so high that the locks at Wilmette would have to be opened, untreated sewage would be dumped into the lake.

Mazzocco said the elevation gauges were at a plus 2 and got to a little over plus 3 at the Wilmette pumping station.

“We were concerned because at that point, reverse flow elevation is a plus 5, so we were about a foot and a half away from going back into the lake,” he said.

By 2:00 pm, after the storms had moved on and the water levels in the system had gone done, it was time to go into recovery mode. By 3:00 pm, the flow in the system at Lockport had dropped from the high of 20,000 cfs to 10,000 cfs. The threat of opening the locks had been avoided.

But with more rain and flash floods in the forecast, the minute-by-minute management of the area’s waterways is far from over.