By Patricia A. Scheyer
NKyTribune reporter
The Campbell County courthouse in Newport was the site of a report and discussion on solutions to the repeated flooding in the city of Silver Grove by members of the United States Geological Survey and members of the US Army Corps of Engineers.
Map shows Silver Grove in relation to the river.
The main speakers at the meeting last week were Cindy Minter, Director of the Planning and Zoning in the county, Justin Boldt, from the USGS, Tammy Markert, AICP, a Planner in the US Army Corps of Engineers, and Ken Lamkin, PE, Hydraulic Engineer with the US Army Corps of Engineers.
Together they painted a picture of the almost century-long flooding that has beset the city of Silver
Grove again and again. The city of Silver Grove is about 9 to 10 miles upstream from Cincinnati.
“As you can see there is a long term stream gage at Cincinnati which is also a National Weather
Service forecast point, and prior to this study, that was the only source of river information and forecast information that the city could rely on,” said Boldt. “There are two additional stream gages that are new as part of the study in Silver Grove. This poses a unique situation that we don’t see in a lot of other cities in that there are two independent flooding sources, the Ohio river and Fourmile Creek.”
Justin Boldt from USGS, Ken Lamkin and Tammy Market from US Army Corps of Engineers.(Photos by Patricia Scheyer/NKyTribune)
He said Fourmile Creek can flood and present a lot of problems, but if the Ohio River rises, it can
back up into Fourmile Creek and create the flooding, hence the two independent sources.
“Just to give a little background on flood impacts for contacts, 60 feet at the Cincinnati gage is
about an elevation of 492 feet in Silver Grove,” Boldt explained. “The first property is impacted around 485 feet, and once you get above 490 feet thats when you start to get into some significant residential impacts. Highway 8 at Fourmile creek crossing is overtopped at 492 feet.”
He explained that the tasks for this study were divided in two, and the USGS would install two new stream gages, develop and calibrate a hydraulic model, then work on a flood inundation mapping, and look at different flood risk mitigation alternatives.
The Corps of Engineers worked through their flood plain management services program and developed a hydrologic model for a rainfall run off model. They also developed 8 design frequencies for Fourmile Creek which had not existed in that detail before. and lastly, they determined the preliminary economic analysis for the proposed alternatives.
The flood risk mitigation alternatives that the study came up with are flap gates to prevent the
Ohio River from backflowing into Four Mile Creek, detention basins, somewhere upstream of the city to
help reduce headwater flooding down Fourmile Creek, and increased culvert sizes, at Tiemeier Lane,
Highway 8, and the CSX Railroad which would reduce headwater flooding by increasing water flow out of
the city and into the Ohio River.
Flap gates, they found, would prevent backflow, but the gates could not remain closed for long, and the water from Fourmile Creek would be prevented from leaving the city.
The detention basins that were considered were two sizes, 25.8 acres with a storage of 244 acre-ft, which is a measurement of volume of water, or 97.4 acres with a 946 acre-ft storage. They discovered that the smaller basin would not store enough water to help with the problem, and the bigger one would make more of the difference, but where would they put that large of a basin near the city.
Cindy Minter, county Planning and Zoning
The third option would be increasing the size of the culverts, and that appears to have the
potential of the most relief.
The existing diameter of the culvert A at Tiemeier Lane is 18.5, and could be increased to 28.5 feet in diameter. Culvert B’s solution would be to replace the culvert with single span bridge similar to
Messmer road or Uhl road. The solution to Culvert C would be to replace the culvert with a single span
bridge at Tiemeier Land, and increase the size of all culverts under Highway 8 and the CSX Railroad.
Analysis of the cost amount of damage that could be prevented by these mitigation alternatives vary greatly. The greatest amount of damage that would be prevented by the large detention basin was estimated at 86.92 percent, and the corrections to culvert C were estimated at 99.98 percent of the
damage.
The city of Silver Grove has several new sources of information which will help them better understand flood risks, as well as help them with decision making. These are stream gages, a hydraulic model, flood inundation maps, flood risk mitigation alternatives, and preliminary economic analysis.
Cindy Minter said they were looking at grants to help with possible solutions.
“The next phase is to work on the trade off of benefit,” Minter said. “It may take more than five years to get a return on investment. Then we have to know how many years the entire project would
take, and is it worth it.”
She acknowledged all the efforts of Silver Grove, Campbell County, and others to put up funds to get the gages and put them in the fields so that now they have a more complete picture of what the situation is, but she cautioned that like all other projects this will take more time.
“Now is the time to start talking about this,” Minter said. “Because in two years I will need it.”
All the information is promised to be up on the Silver Grove website within a month.
