Doug McCarty thought that the ground felt a little soft at a spot behind the Harrison County Fire District Office, formerly Curves. When he kicked at it, the unexpected happened. The ground fell away revealing a sink hole estimated at about 12 - 15 feet deep.
Gary Royalty, Cynthiana Director of Public Works, joined a crew to investigate. They taped off the area and excavated a sinkhole approximately three to four feet in diameter, he said.
The sod covering the hole was less than a foot thick, Royalty continued. The only thing holding the top in place was a network of grass roots. It is difficult to determine how long the sod had been that thin, but the hole itself, Royalty said, has been decades in the making.
For safety reasons, the public works office excavated the surface area of the sink hole, roped off the area in yellow tape and covered the opening with a large slab of metal. However, no one went down in it for a closer look, Royalty said.
In the meantime, Royalty said the city received excellent cooperation from the county and especially from Kevin Florence and the state road department.
The road department let the city borrow a highway excavator which was used to open up the sinkhole and cover the opening, he said.
A check of the grounds surrounding the hole has shown the remaining area to be solid, he said, but people should keep their distance.
Six storm drains located throughout Cynthiana meet at a catch basin near where the sinkhole was discovered, Royalty said. The catch basin emptied water into a hand-laid rock culvert well over a dozen feet underground. The culvert, measuring approximately 24 inches, is lined with field rocks and capped with thick, long field stones. It channels storm water into the river.
The culvert is very old, Royalty said, but most of the time they are reliable and resistant to erosion. “There are two other culverts of similar construction in downtown. One runs down Pike Street,” he said.
The likely cause of the sinkhole is that one of the culvert’s underground capstones broke which allowed rushing water to slowly erode the ground above.
Interestingly, the area where the culvert has been draining into the river shows what several decades worth of erosion can do to the ground.
The city is going to move ahead with plans to retire the old culvert, Royalty said. These plans will add a new catch basin and install materials to drain the water to another point at the river, he said.
The old rock culvert will be sealed off and filled with permanent structural material, he said.
Debbie Peak, whose office at the Fire District is about 10 feet from the sinkhole, has a window that allows a clear view of the area. She shuddered at the thought of how many people she has seen standing in that area.
Fortunately, she said, the problem was discovered before anyone got hurt.