Nobody ever said fixing Elmhurst's flooding problems would be easy, and outside engineers July 18 presented a number of difficult choices the City Council will have to make.
Christopher Burke of Burke Engineering and Alan Hollenbeck of Wheaton-based RJN Group discussed their four months of research during this week's City Council meeting. They identified Elmhurst's flooding woes, as well as preliminary solutions.
Hollenbeck handled sanitary sewer research.
RJN teams monitored spring rains and did flow testing. They looked for areas the sanitary pipes interact with the storm sewer system, which allows the inflow of “clear” storm water to be unnecessarily processed by the sanitary system.
Hollenbeck discovered an "average peaking factor" of 15, 18 and 25 for north, southwest and southeast Elmhurst, respectively. Peaking factor is the ratio of the maximum flow to the average daily flow in a water system. An average peaking factor greater than 10 indicates a "severe problem." High inflows and infiltration of clear water into the sewer system in southeast Elmhurst led to basement backups that plagued southwest Elmhurst last summer, Hollenbeck said.
and clean check valves are two options Hollenbeck suggested for those residents who experience sewage backup in their basements. The city offers a subsidy for overhead sewers, which Hollenbeck admitted are "a very expensive and a disruptive type of construction"; a clean check valve is an alternative for those unable to install an overhead sewer. (See slides 18-25 in attached presentation.)
Another problem in south Elmhurst is older homes with foundation drains directly connected to the sanitary sewer. Burke said any home built before 1968 likely has this type of drain, which is expensive and cumbersome to dig up and disconnect.
Burke added that 64 houses in southwest Elmhurst, alone, have reverse-slope driveways, which is another flawed trait of the city's older housing stock.
"If we were able to develop Elmhurst the way we would like it to be built today, knowing everything we know about stormwater management, we would probably not recommend … reverse-slope driveways," he said. "We would design these areas a lot different."
Retrofitting Elmhurst to mitigate flooding could be a difficult proposition as well. Burke outlined some possible solutions that require construction of thousands of feet of relief sewer, and possibly converting green spaces, such as York Commons Park, into a water storage area.
Burke did not have costs associated with such improvements, but he did admit his preliminary alternatives would be far from fool-proof. For example, the area of Vallette Street and Swain Avenue would still only have a “five-year-storm level” of flood protection after any proposed improvement is completed. A five-year storm refers the level of storm intensity likely to happen once every five years.
And even those solutions would only be possible if the city can convince other bodies, such as District 205 and the Elmhurst Park District, to use their properties for water storage. Aldermen said Monday that local taxing bodies are aware of the suggestions that may come from Burke's comprehensive plan on flooding.
"We have not only whispered in their ear, we have screamed in their ears ... that these are potential solutions that may be coming forward," 6th Ward Alderman Jim Kennedy said.
Burke said another option, buying out flood-prone homes in low-lying areas prime for water storage, has not yet been considered, but he didn’t rule it out.
The outside consulting team will continue to study the situation throughout the fall before making a final presentation of the comprehensive plan for flood mitigation and associated costs in November.
Fifth Ward Alderman Chris Healy said the reality of the situation is the city has to keep the water out.
"This information shows us that the problem isn't what to do with the water. The problem is, how do we stop the water from getting into the system?" he said Monday.
"The bottom line is, when Mother Nature wants to win, she's going to win."