Clarksville Drainage Guide: Sinkholes, 811, Permits (2026)

Updated October 19, 2026. This guide is general information, not legal or engineering advice. Rules change, so confirm with the agency listed before you start work.

Quick reference

Topic	What to know	Source
Rainfall	About 53.5 inches of precipitation a year (1991 to 2020 normals)	NOAA normals via Wikipedia
Soils	Highland Rim soils over limestone; clayey, cherty subsoils on slopes	UT Extension
Sinkholes	Common in Montgomery County; don't fill, dump in or drain to them without advice	Montgomery County Stormwater
Draining into a sinkhole	Increasing runoff into one needs a TDEC UIC permit	Montgomery County; TDEC
Buffer	60-foot undisturbed buffer around sinkhole throats, caves and Class V wells	Montgomery County Stormwater
Before digging	Tennessee 811: free, at least 3 working days' notice, homeowners included	Tennessee 811
Contractor license	Required for projects of $25,000 or more	TN Board for Licensing Contractors
Home improvement license	Over $3,000 to under $25,000, only in 9 counties; Montgomery isn't one	TN Board for Licensing Contractors

Why do Clarksville yards hold water?

Clarksville averages about 53.5 inches of precipitation a year based on the 1991 to 2020 climate normals. The city sits on the northwest edge of the Highland Rim, and University of Tennessee Extension describes Highland Rim soils as underlain by limestone, formed from thin loess and limestone residuum, with clayey and cherty subsoils on sloping ground. Clay subsoil accepts water slowly, so heavy rain either runs off or ponds. Most drainage fixes here are about moving water across or through the top layer of soil to an outlet, rather than expecting the ground to absorb it.

What are the rules about sinkholes?

Montgomery County's stormwater program explains that sinkholes form when water moving through cracks dissolves the limestone until the soil above collapses, and that they're common in the county. Its guidance says:

Sinkholes are hard to stabilize permanently and can grow or re-form after filling, so consult a civil engineer or geotechnical professional before altering one.
It's illegal to put any substance on the ground that can be washed into a sinkhole, and dumping dirt, yard waste or building materials in or around one is prohibited.
Stormwater regulations require a 60-foot undisturbed buffer around throats, cave entrances and Class V injection well structures.
Any change that increases runoff into a sinkhole must be permitted by TDEC's Underground Injection Control section.

The county's karst feature policy treats any closed depression in karst terrain as a sinkhole. Its preferred option is to leave it untouched. Remediating one requires geophysical surveys by a Tennessee-licensed geotechnical professional or engineer and a $25,000 bond held for five years, and converting one to a Class V injection well requires an engineering plan, a TDEC permit and a bond. The county says it does not advocate creating injection wells.

Do dry wells need a state permit?

TDEC's Underground Injection Control page says anyone who discharges stormwater into a subsurface system must submit a UIC application, and its Class V form covers stormwater discharge to the subsurface or modification of a karst feature. Class V wells are generally authorized by rule, with review that typically takes two to four weeks. If a contractor proposes a dry well or any buried system that releases stormwater underground, ask whether a UIC filing is needed.

Do I have to call 811?

Yes. Tennessee 811 says the locate requirement applies to both professional excavators and homeowners, the service is free, and a normal request needs at least three working days' notice. Tickets are valid for 15 calendar days after the legal start date. If you hire an excavator, the excavator needs its own ticket. In Oak Grove and the rest of Kentucky, use Kentucky 811.

What licensing does Tennessee require?

The Tennessee Board for Licensing Contractors requires a contractor's license for projects of $25,000 and up. A separate home improvement license covers residential remodeling of more than $3,000 to less than $25,000, but only in counties that have adopted it: Bradley, Davidson, Haywood, Hamilton, Knox, Marion, Robertson, Rutherford and Shelby. Montgomery County isn't on that list. Electrical, plumbing and HVAC work have their own requirements, which can matter for sump pump wiring.

Questions to ask a drainage contractor

Where exactly will the water go, and will it affect my neighbors?
Is there a sinkhole or karst feature nearby, and does this job need a TDEC or local permit?
Who will call Tennessee 811, and when?
If the job is $25,000 or more, what's your Tennessee contractor license number?
What pipe, fabric and gravel will you use, and how can the system be cleaned out later?
What's warrantied, and for how long?

Common questions

Is it legal to fill a sinkhole in Montgomery County?

The county's preferred option is to leave sinkholes untouched. Remediation requires geophysical surveys by a licensed geotechnical professional or engineer and a bond, so get professional advice first.

Do drainage contractors need a license in Tennessee?

A contractor's license is required for projects of $25,000 or more. Montgomery County hasn't adopted the separate home improvement license for smaller jobs.

How much notice does Tennessee 811 need?

At least three working days for a normal locate request. It's free, and homeowners are required to call too.

Montgomery County yard drainage guide (2026)