CEDAR RAPIDS — Public Works Director Dave Elgin said last week that the damage to homes and cars on some streets as a result of the late June flash flooding means that the city has work to do to identify how its public sanitary and storm sewer systems can perform better next time.

Elgin said the city has 12 watersheds that flow through it to the Cedar River, and nearly all of them caused some problems in the “extreme event” of late June.

He said it is likely some sewer pipes will need to be enlarged in the city’s system along with the use of other tactics such as additional detention areas to slow stormwater runoff.

The city’s 667 miles of sanitary sewer and 512 miles of storm sewer are separate from each other. But the two systems played some role in the damage left by the recent flash flooding.

In some instances, the city’s storm sewer system could not handle the rainwater, which sent the water onto streets and then sometimes into basements and down sanitary sewer manholes and directly into the sanitary sewer system.

Overwhelmed storm sewers helped to overwhelm sanitary sewers, city officials said.

Jon Durst, the city’s sewer superintendent, said more frequent heavy storms and heavier storms likely will factor into the future design of the city’s sewer systems, which he said could translate into some bigger sewer pipes.

At the same time, Durst said it might be impossible to design a system that entirely handles an event such as the flash flood that hit the city last month.

It is incorrect to say that the city hasn’t been improving its system, Elgin said.

It was only in the past few years that the city finally — under the direction of the U.S. Environmental Protection Agency — renovated and enlarged its sanitary sewer system in places to comply with an order that it no longer use temporary pumps to pump sewage during heavy rains from the sanitary sewer into the storm sewers in the street that run to the river, as a way to avoid sewage backups.

The last two of what had been 22 in-manhole pumps were eliminated on West Post Road NW at a cost of $500,000 and at E Avenue NW at 15th Street NW for $3.7 million, according to city figures.

Twenty years ago, Elgin said, the city would receive 600 calls about sewer backups in a year.

According to city figures, backup calls in 2003 attributable to a blockage in the city system from tree roots, large objects or pipe collapses numbered 103. That year the city said it established a more thorough program to replace, reline, clean out and use video inspections in its sanitary sewer system.

The number of sewer backups attributable to the problems in the city’s system generally has declined, one year to as few as 13.

Durst said the city received 122 calls about sewage backups from June 20 through July 11, but only two were because of a blockage or defect in the city’s sanitary sewer system.

Big storms, he said, don’t change the numbers on the performance of the city’s system. But he said that doesn’t mean the city doesn’t track calls about backup issues even as the city system is not blocking anything.

“We are not trying to bury numbers here,” he said. “We have all the other numbers. We understand there are problems.”

Elgin said the city’s sanitary sewer and storm sewer systems can handle what comes at it 99 percent of the time. It even can handle heavy rain that falls on dry ground.

It is the especially heavy rain on already saturated ground that is the challenge, he said.