A sinkhole four feet deep and four feet wide has opened up near the low head dam on Youngs Creek in Province Park.
The sinkhole caused some water to be sucked under the dam, forming a whirlpool about two feet below the dam.
Combined with the high flow created by Friday night and Saturday morning storms, the water under the dam is churning more powerfully than usual. The dangerous whirlpool is a few hundred feet from a playground and shelter house.
The City of Franklin was notified of the whirlpool on Friday, said Mark Richards, city engineer.
The city put up caution tape to warn people to stay away from the area until the sinkhole can be filled, Richards said.
City officials did not think to warn the public because there are already signs posted near the dam indicating a dangerous undertow, he said.
“Kids shouldn’t be in the creek there anyway. It is posted that it is dangerous to be in the creek at the low head dam already. The sinkhole did not increase the risk,” Richards said.
City officials are working with Johnson County Surveyor Gregg Cantwell on short- and long-term solutions to fill the hole. Youngs Creek is a regulated drain, and maintenance is under the county’s jurisdiction.
The sinkhole reduced in size over the weekend because sediment was deposited into it by the strong waters from Friday and Saturday thunderstorms, Cantwell said.
In the short term, the county plans to fill the hole with rip rap, a construction material composed of large rocks strung together with wire netting. A metal plate is also being placed on top of the hole, he said.
The county has hired a contractor to do the work Wednesday, and it will cost about $3,000, Cantwell said.
The sinkhole likely opened up over time because the force of the water coming off the dam eroded the creek bottom, he said.
Cantwell is still working on a long-term fix but expects to have more information about that later this week, he said.
