By Henry Christner
Times-Dispatch Staff Writer
Published April 10, 1994
CHERRY GROVE
One of the most popular spots for Sunday outings and community picnics around Harrisonburg in the 1920s was a stretch of rolling farm pasture near here.
The attraction in this part of Rockingham County was not a scenic river or idyllic millpond but a hole in the ground. At one moment, water would pour from the hole, sometimes at a rate of 1,000 gallons a minute. A short time later, the water would shut off abruptly, like a faucet.
No one knew why.
In 1936, a state geologist, R.C. Cady, described the flow as uncanny, and added: "It seemed as if its behavior were manipulated by mischievous elves residing in the caverns . . . who take great delight in bewildering and mocking those who endeavor to discover its laws of flow.
Another scientific observer who tried to make sense of it was Thomas Jefferson, who speculated about the site in his 1787 book, Notes on the State of Virginia. A most uncommon spring, he wrote.
The object of this two-century-old puzzlement is Tide Spring, so named because its strange behavior reminded early settlers in Rockingham of ocean tides. But tidal action has nothing to do with it.
The spring belongs to a class known by several different names — ebb and flow spring, periodic stream, temperamental spring, and breathing spring. Only a handful exist in the world, and Tide Spring is one of the most unusual.
During a typical flow pattern, the water will suddenly begin running from the opening in the ground. When it reaches its peak in four or five minutes, the water will have filled up a gulley that leads from the opening to a nearby creek, Tide Spring Branch. Then, 10 minutes after the flow began, the water will stop. Sometimes, the current even moves backwards.
Why does this happen?
* * *
Jim Lehman of Harrisonburg, who has studied Tide Spring for years, thinks he knows, although some of the details of the explanation still elude him.
Since boyhood, he has been intrigued by the mysterious stream. He first visited the site with his father, Daniel, a teacher who moved from Pennyslvania to Rockingham in 1918. As an adult, Lehman also became a teacher, at George Wythe High School in Richmond in the 1970s and later in the physics department at James Madison University in Harrisonburg.
It was at JMU that Lehman did a five-year study of Tide Spring, building on work done at the site in the 1920s by Oscar Meinzer, a geologist with the U.S. Geological Survey and the author of Physics of the Earth, published in 1942.
Meinzer did extensive monitoring of flow patterns, but neither he nor Cady came up with an underground profile that would explain why Tide Spring behaves the way it does. That unanswered question was what motivated the study during the 1980s by Lehman and his associates in the field, Randy Fear and Henry Leap.
The team monitored flows, kept detailed records on rainfall, and studied the impact of seasonal precipitation on the amount of water generated by the spring. Lehman concluded that Tide Spring is fed in the same manner as other ebb-and-flow springs — by an underground reservoir somewhere near the surface opening.
The team then developed a model they hoped would help them find the reservoir and estimate its size. Most important, they wanted to understand why Tide Spring's abrupt off-and-on flow was so different from the others.
* * *
As it turned out, one of the original researchers on this topic — Jefferson — proved to be correct in his assessment of the nature of the spring. He concluded that Tide Spring was a Syphon fountain.
Tide Spring does indeed function as a siphon, but what makes it different is that it's a self-cycling siphon, said Lehman, who wrote about his findings in the Journal of Geological Education in 1990.
The subterranean reservoir lies somewhere beneath the surface, carved out of layers of limestone and dolomite that are common in western Virginia. The water in the reservoir comes from precipitation absorbed from the surface. An underground channel leads from the reservoir to the surface, and pressure changes create a siphoning effect that periodically cycles water through the channel to the surface.
What makes Tide Spring even more quirky is its habit of flowing backwards.
The reversal occurs when, during a flow, the reservoir stops releasing water into the channel; at that point, the momentum of the forward-moving mass of water causes the discharge end of the flow to be temporarily higher than the source end. As the water adjusts itself to a common level, the flow reverses.
* * *
Although Lehman now understands Tide Spring as well as anyone, he is still trying to find the underground reservoir. He has estimated the reservoir must be about 160 feet from the opening.
Because the siphoning action is turbulent and noisy, Lehman has tried to listen for the reservoir by burying a microphone 3 feet in the ground at various likely locations. So far, after about 100 attempts, he's still not certain.
The upshot is that Tide Spring still retains some of its mystery; it still intrigues those who hike across the farm pasture to see it. The site remains a popular destination for school field trips and natural history buffs.
Even the cattle on the farm, which is owned by Glen Showalter, also enjoy the spring, so much so that the opening has been blocked off by timber. That barrier gives Tide Spring some extra room to ebb and flow, and to keep on keeping on.
