By Peter H. Milliken
The Meander Creek Reservoir dam must be able to withstand a flood that would result from nearly 20 inches of rainfall within 24 hours, according to an engineering consulting firm. That firm recently presented a series of potential dam- modification strategies to enable safe passage of such a flood.
That deluge, known as the “probable maximum flood,” would result from a 19.32-inch rain within 24 hours, said Anthony Vigorito, chief engineer at the Mahoning Valley Sanitary District, which has budgeted $3.5 million for repairs and improvements to the 1924-vintage dam and its spillway.
That theoretical event would be nearly three times the 6.88-inch rain within 24 hours, which the National Oceanic and Atmospheric Administration says is likely to occur here only once in 1,000 years, he added.
Vigorito said the dam is structurally sound and inspected daily by MVSD staff.
However, it is federally listed as a “high hazard” dam, meaning that loss of human life likely would be a consequence of its failure.
As such, it must “safely pass 100 percent of the probable maximum flood,” according to a report from MVSD’s engineering consultant, Gannett Fleming of Harrisburg, Pa.
The dam, which impounds Meander Reservoir, can’t pass a flood of that magnitude without having water flow over the top of its embankment, the report said.
“The depth and duration of dam overtopping would cause erosion of the vegetated downstream embankment slope and potentially lead to failure of the dam embankment” in such a flood, Gannett Fleming said.
MVSD treats Meander Reservoir water and supplies it to Youngstown, Niles and surrounding communities.
Water has flowed only over the dam’s spillway and never over the top of its embankment, Vigorito said.
However, he added that an inflatable rubber bladder installed atop the spillway during the 1990s, which gives the reservoir extra storage capacity in case of a drought, adds to the pressure on the dam.
The 7-mile-long reservoir has a 10 billion-gallon capacity at the top of the spillway, with the bladder adding 1 billion gallons to that.
To help reinforce the dam, MVSD is studying the possibility of raising the concrete core wall within the center of the dam to the level of the concrete road atop the dam, Vigorito said.
The top of that wall is now between 1 and 2 feet below the road.
Gannett Fleming’s report outlined various potential methods of modifying the dam to enable it to safely pass the probable maximum flood, including raising the top of the dam or raising the curb atop the dam.
“The dam obviously is the most important structure in the whole works of any water system,” because it impounds the water source and because its safety is critical to the well-being of downstream residents, Vigorito said.
“We are working to get that project started here as soon as possible,” Vigorito said of the dam improvement effort, adding that the total project cost isn’t known yet.
The project would also include repairs to concrete sections of the dam, where cracking and spalling has occurred, he said.
“It’s a high priority because it first is a safety issue,” Jamael T. Brown, a member of the MVSD board of directors, said of the dam-improvement effort.
“Our top priority is to make sure that we have the most modern facility and factory that produces water in the state of Ohio and bring it up to the 21st century, and that’s what we’re doing right now,” he concluded.