A gentle meltdown

<p>Flooding in Naperville on Thursday, April 18, 2013. City officials do not expect similar flooding as temperatures rise beginning Monday.  | Brian Powers~Sun Times Media</p>

Flooding in Naperville on Thursday, April 18, 2013. City officials do not expect similar flooding as temperatures rise beginning Monday.  | Brian Powers~Sun Times Media

Memories remain vivid of an exceedingly soggy Naperville last spring, but officials don’t expect the unprecedented rising of water seen in April 2013 to recur any time soon.

In a reversal of recent trends, temperatures next week are expected to rise to above-normal levels. With current snow cover in the region ranging from eight to 18 inches, the National Weather Service is warning that could mean an increased flooding risk.

“The water equivalent of the existing snowpack is estimated between 1 and 4 inches,” the agency notes in a news release issued Friday. “Frost depths below the snowpack range from 12 to 16 inches. A deep frost layer can inhibit the infiltration of meltwater from snow and increase the amount of runoff.”

The Weather Service predicts that river waters will begin to rise toward the end of next week, and heavy rain would exacerbate the problem.

“Ideal melt conditions to minimize the degree of flooding would include daytime temperatures rising moderately above freezing, and overnight lows falling back below freezing,” the statement continues.

Bill Novack, head of the city’s Transportation, Engineering and Development department, said he’s scrutinized the forecast and expects that ideal scenario is likely — but city crews will be keeping an eye on things just the same as temperatures moderate.

“Based on what I see and also as deep a frost as we have in the ground right now, we don’t anticipate a large amount of thawing,” he said.

Temperatures should rise slowly enough, he expects, to enable the melting snow to drain away before it has a chance to pool.

“Basically, the thing we’re looking for is if the water does that, it travels to the inlets,” he said. “We will be out looking and say, ‘Hey, it’s ponding a little bit.’”

Occasionally ice builds up at the openings to curb manholes, which send drainage toward the inlets. Crews will check to ensure those locations remain clear. They also will be on the lookout for river ice jams, which impede flow and can lead to buildup of snow runoff upstream. The NWS notes that many waterways in the Chicago region are entirely covered with ice.

“As the runoff begins … flows beneath the ice cover will begin to increase which will lift and break the ice. As the ice moves downstream, ice jams are possible. Ice jams can result in rapid rises of water levels and significant flooding in the vicinity of the jam,” the news statement says.Accumulated ice can cause damage of its own as well. Novack said a railing along the West Branch of the DuPage River, near the Riverwalk amphitheater, was bent by a passing ice floe this winter and will need to be replaced.

Also being replaced in some Naperville homes is the system for managing potential sewer backups of the sort that struck hundreds of residents last April. It’s another targeted tactic being employed to keep water woes at bay.

The city stepped up its sanitary sewer backflow prevention program last year, after many homeowners complained of foul water flooding their basements in the aftermath of the heavy April rains.

“The program is for those who have had a prior history of sanitary sewer backup, or if they’re in an area that’s prone to sanitary sewer backup,” said Jim Holzapfel, director of wastewater for Naperville.

Nearly 400 applications were circulated to homeowners known to be in that group, but others may apply for the program and the Water Department will inspect the property for consideration, he said. Those who qualify are reimbursed by the city for 75 percent of the upgrade’s cost, which they arrange directly with contractors they select. The cost averages around $4,000, but can vary a bit.

“Because everybody’s basement is a little bit different, their situation is a little bit different,” Holzapfel said.

The city also accelerated the timeline for relining some of the clay sewer pipes in the Cress Creek neighborhood, which was especially hard-hit by backups last spring. The $2.4 million project is targeting about 10 miles of piping; about 100 miles’ worth of pipe citywide have already been fortified by the thick polyester, epoxy-enhanced material.

Sometimes homes take on water from another sort of natural cause. Holzapfel said tree roots, especially from willow trees, are a frequent culprit. They can clog pipes and cause backups after making their way through small gaps in concrete pipe joints, even in relatively new sewer systems. City crews were especially surprised, Holzapfel said, to encounter the problem in Tall Grass, one of the city’s newer subdivisions.

“It’s amazing — they weren’t that old! Basically when you have a big event like last April, we say, ‘Holy smokes, we’re having flooding there,’” he said. “The great thing is we’ve got the equipment and can go in and fix those problems.”