UPDATED: Thursday, June 27, 9 a.m.
The National Weather Service early Thursday issued a flood watch for the Des Plaines River at Riverside, downgrading the potential for flooding in that area. While the river has topped flood stage further north in places like the village of Des Plaines, the river had not approached flood stage in Riverside as of 7:45 a.m., when the river level was 5.92 feet. Flood stage in Riverside is 7 feet, and the National Weather Service now says minor flooding is still possible in low-lying areas near the river. The flood watch is in effect until late Thursday night.
Moderate flooding is forecast for the Des Plaines River at Riverside by Friday morning, according to the National Weather Service, which has also issued a flood warning for northern Cook County and a flash flood warning for a good part of northern Illinois.
While rains in this area have not been particularly heavy and river levels are close to normal, heavy rains north of Chicago have created flood conditions and swollen river levels. That water has begun to make its way downstream toward Riverside.
As of 10:45 a.m., the Des Plaines River level was at 3.4 feet, well below the 7-foot flood stage. However, by about 9 a.m. on Friday, the National Weather Service is predicting that the Des Plaines at Riverside will have risen to 8 feet, which will cause moderate flooding in the park and wooded area near the river and may begin to affect some roadways, such as First Avenue.
In Brookfield, Salt Creek is also at a normal level at this time. There is no stream gauge in the village, but in the closest upstream gauge in Western Springs, the level was at about 2.5 feet at 9:50 a.m.
However, further upstream Salt Creek has risen sharply in some instances, according to U.S. Geological Survey gauges on the river. In Rolling Meadows, the level of Salt Creek jumped more than 7 feet since yesterday.
Meanwhile, Allison Fore, director of public affairs for the Metropolitan Water Reclamation District of Greater Chicago, said that one of the three main deep tunnel branches — the main stem tunnel, which services the city of Chicago and northern suburbs — is already at 100 percent capacity.
The Des Plaines tunnel, which serves the western suburbs, is at 70 percent, said Fore. The deep tunnel system collects waste from combined sewer systems (ones containing both storm runoff and sanitary waste) and prevents it from entering natural water ways like the Des Plaines River and Salt Creek.
Once 100-percent capacity is reached, the MWRD closes the gates that accept that combined sewer discharge, which redirects the combined sewer runoff into the natural waterways, which increases water levels, according to Ed Staudacher, supervising civil engineer for the MWRD.
“We encourage the public to minimize use of water in their homes during storms events to reduce the water going into the sewer system,” said Fore.