What a sinkhole is
Montgomery County's Building and Codes Department publishes sinkhole guidance for property owners. It explains that water moving through cracks in limestone slowly dissolves the rock. When enough is gone, the soil above collapses into a cone-shaped hollow. The county calls sinkholes a common feature of the area and warns that, once formed, one can grow unpredictably.
What the county tells owners
- Do not try to fix it yourself
- Sinkholes are hard to stabilize and may reopen after filling. Filling can also change how surface water and ground water flow. The county says to consult a civil engineer or geotechnical professional before any attempt to alter one.
- Keep a buffer
- County stormwater regulations require a 60-foot undisturbed buffer around sinkhole throats, cave entrances and injection wells, to protect ground water.
- Nothing goes in
- It is illegal to dump trash, dirt, yard waste, building materials, animal waste or chemicals in or around a sinkhole. Water entering one goes straight to the ground water.
- More runoff needs a state permit
- Any change that increases the runoff directed into a sinkhole must be permitted by the Tennessee Department of Environment and Conservation's Underground Injection Control section.
Why this matters for waterproofing
Every drainage job ends with a pipe that lets water out somewhere. On a lot with a depression at the back, that depression is the tempting place. Under the county's guidance, a French drain, a downspout run or a sump discharge that adds water to a sinkhole is not a casual choice. It is something that needs a permit.
Heavy equipment is a second concern. The county points out that the rock under a sinkhole may be unstable and that vibration from construction can make it worse. A trench or an excavator belongs well away from the edge.
If you have a depression in the yard
- Tell the company about it before it designs anything, and walk the yard together.
- Ask where every pipe will discharge and how far that is from the depression.
- Do not let anyone fill it with soil, rubble or brush as a favor.
- If it is new, growing or close to the house, speak with the county Building and Codes office at 931-648-5718 and with an engineer before any drainage work.
Inside the city
The county rules above apply outside the Clarksville city limits. The city's stormwater page asks people to report anyone dumping into storm drains or sinkholes, and the city's Street Department handles drainage maintenance and drainage complaints. For a sinkhole on a city lot, start there.