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‘It’s imperative that we address this issue’: Study finds weaknesses in Piney Run Dam

The earthen dam at Piney Run lake is pictured Wednesday, October 9, 2019. The county has contracted a watershed study of the reservoir following an MDE Dam Safety spillway capacity analysis of the dam in 2016.
The earthen dam at Piney Run lake is pictured Wednesday, October 9, 2019. The county has contracted a watershed study of the reservoir following an MDE Dam Safety spillway capacity analysis of the dam in 2016. (Dylan Slagle / Carroll County Times)

Findings from the Piney Run Watershed study found weaknesses in the Piney Run Dam and an obstacle to activating the watershed’s water supply; and solutions may require the reservoir to be closed for a period of time.

The results of the two-year study were presented to the Board of County Commissioners on Thursday morning by AECOM, a contractor hired by the commissioners to conduct the study.

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The water of Piney Run Reservoir, which is a beloved recreational locale for boating and fishing, is held back by Piney Run dam which is the largest dam the county owns and maintains.

The study was requested by the Maryland Department of the Environment, or MDE, after an annual inspection lead to concerns over the dam’s security in the scenario of extreme flooding. The county was then given until 2027 to address any issues the study found.

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Carroll County commissioners contracted the study to AECOM, an engineering firm, in July 2019. A public hearing about the study was held in February 2020, right before the COVID-19 pandemic with another set of virtual public hearings about the studies findings scheduled for March 11 on Zoom.

Michael Greer, left, and Timothy King of AECOM, an engineering firm, head out onto Piney Run lake Wednesday, October 9, 2019 to conduct a bathymetric survey of the reservoir, part of a watershed study undertaken by the county following an MDE Dam Safety spillway capacity analysis of the earthen dam at Piney Run.
Michael Greer, left, and Timothy King of AECOM, an engineering firm, head out onto Piney Run lake Wednesday, October 9, 2019 to conduct a bathymetric survey of the reservoir, part of a watershed study undertaken by the county following an MDE Dam Safety spillway capacity analysis of the earthen dam at Piney Run. (Dylan Slagle / Carroll County Times)

In addition to holding back Piney Run Reservoir, the dam, which was constructed in 1974, has other water sources that flow into it. At the time of construction, the county had three purposes for the dam including flood control, recreation, and to provide water supply for the county, a feature of the dam that to date has not been used.

Currently the dam is classified by MDE Dam Safety as a high hazard dam and is the only high hazard dam the county owns.

At any given point in time there is approximately 54 feet of standing water behind the dam according to Christopher Heyn, Bureau Chief of Resource Management for Carroll County. Heyn warned the commissioners at Thursday’s board meeting that in the case of a large storm additional water could stack up behind the dam.

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“If the dam were to catastrophically fail, that would release a floodway down the stream valley and just downstream we have Md. 32,” Heyn said. “When that wave hits Md. 32 it would still be 30-40 feet deep, so you can imagine that would be a catastrophic impact.”

Heyn said the Department of Resource Management conducted a study on the possible effects of such an event on the surrounding area and found that there are more than 240 properties and 40 road crossings downstream from the dam that would be impacted.

In it’s classification of the dam as high hazard, MDE specifically raised two concerns about the dam — whether the dam’s auxiliary spillway, a passage for surplus water, is large enough for storm water to flow safely in the event of a large storm and whether the spillway could erode and potentially cause the dam to fail.

Jeff Blass, a dams engineering project manager with AECOM, said their study found that the spillway does not have the capacity of passing storm water without overtopping the dam and in the scenario of extreme weather, the dam would be over the top by several feet. The study also found that the spillway is in fact erodible, as a result of being built on a combination of soil and highly weathered rock.

AECOM also presented solutions to these problems including widening the spillway and taking the earth that would be mined from the spillway to raise the dam. To combat the erosion, Blass recommended the concrete armoring of the downstream spillway.

Along with addressing concerns with the dam, Heyn and Blass presented the commissioners with options to tap in the reservoir’s potential to supply water. Though sedimentation had occurred to the dam, resulting in a loss of water volume, Heyn said that additional water can be put into the reservoir to restore the volume for water supply purposes. This would first require draining the reservoir.

Timothy King, left, and Michael Greer of AECOM, an engineering firm, prepare GPS connected sounding equipment Wednesday, October 9, 2019 before conducting a bathymetric survey of the reservoir, part of a watershed study undertaken by the county following an MDE Dam Safety spillway capacity analysis of the earthen dam at Piney Run.
Timothy King, left, and Michael Greer of AECOM, an engineering firm, prepare GPS connected sounding equipment Wednesday, October 9, 2019 before conducting a bathymetric survey of the reservoir, part of a watershed study undertaken by the county following an MDE Dam Safety spillway capacity analysis of the earthen dam at Piney Run. (Dylan Slagle / Carroll County Times)

Ultimately the commissioners will have to decide whether to fix the dam’s weaknesses and tap into the water supply or just focus on fixing the dam.

Commissioner Eric Bouchat, R-District 4, raised concerns over dam’s functioning in a hurricane.

“In the cycle of hurricanes, we’re due for one in probably the next 25 years of the same size. I think it’s imperative that we address this issue while we can,” Bouchat said.

Bouchat also expressed interest in tapping into the reservoir’s water supply, stating that doing so could help Carroll County gain independence in it’ water supply. The county is currently dependent on Baltimore City for it’s water supply.

Ed Rothstein, R-District 5, agreed with Bouchat and stated that a temporary shut down of the reservoir to activate the water supply would be beneficial in the long run.

“It’s a balance between the community losing a recreational facility for a finite time period to establish a water source for a much greater period of time,” said Rothstein.

Heyn also stressed that it was in the county’s benefit to secure additional options for the county’s water supply.

“Part of the reason we are looking to bring the reservoir online is for redundancy and security in water supply,” Heyn said. “Yes, we do purchase water from Baltimore city, but that is a sole source and a system should have redundancy in it. So this would be a secondary source of water if something was to happen where we would not have access such as a drought.”

The earthen dam at Piney Run lake is pictured Wednesday, October 9, 2019. The county has contracted a watershed study of the reservoir following an MDE Dam Safety spillway capacity analysis of the dam in 2016.
The earthen dam at Piney Run lake is pictured Wednesday, October 9, 2019. The county has contracted a watershed study of the reservoir following an MDE Dam Safety spillway capacity analysis of the dam in 2016. (Dylan Slagle / Carroll County Times)

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