French drain trench in a back yard with gravel bedding and black drain pipe going in

08 · Drainage Solutions

Drainage in Nashville: french drains, swales and culverts

“We design and install drainage systems … that direct water away from structures.” Before any of that, we work out where the water is coming from, because the fix depends on it.

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Find the source before picking the fix

Wet yards have a handful of causes. Roof water dumped at the foundation by short downspouts. Runoff from the hill or the neighbor’s lot above. Ground that has settled and now tips toward the house. Groundwater or a seep that comes up from below after a long rain. Each one has a different answer, and a drain built for the wrong one just buries money in the yard.

The best time to look is during a rain or right after one. Where the water enters the property, where it stands, and where it would go if it could are what the design is built around. Photos and short videos from your phone during a storm tell us more than anything you can describe on a dry day.

The fixes, and when each one fits

Many yards need two of these working together: a swale for the water coming downhill and a french drain for the low spot that stays wet.

Regrading, when the ground beside the house slopes the wrong way
A swale, a shallow grassed channel that carries runoff around a house or across a yard
A french drain, a gravel trench with perforated pipe for ground that stays soggy
Solid pipe from the downspouts, so roof water leaves underground instead of at the wall
A culvert, a pipe under a driveway or path that keeps a ditch flowing

How a french drain is built

The trench is dug with a steady fall from the wet area to an outlet, lined with filter fabric and bedded with washed stone. Perforated pipe goes on the stone, more stone covers it, and the fabric wraps over the top so silt can’t clog the gravel. Topsoil and sod or seed go back on top.

The outlet matters as much as the trench. The water has to come out somewhere lower, at a pop-up emitter, a ditch or open ground that can take it, without just landing in the neighbor’s yard.

When drainage work needs Metro’s grading permit

Metro Water Services counts pipes, ditches and changes to drainage channels as land disturbance, along with filling and excavating, and requires a grading permit once the disturbance passes 10,000 square feet. A french drain across one backyard is usually far below that. Re-cutting a ditch along a property line or piping a channel on a larger lot is the kind of job where the permit question comes up.

What this covers

French drains
Swales and culverts
Water away from structures

Talk it through

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Answers

Questions about drainage

How do I know if a drainage problem is worth fixing?

It is worth fixing when water reaches the house or keeps damaging the yard. Water pooling against the foundation, a damp crawlspace, mulch and soil washing out in every storm, or standing water that lasts days after rain all get worse with time. A puddle on the lawn that drains within hours is usually not worth digging for.

How much does a french drain cost?

A french drain is priced mostly by its length and depth and by how far it has to run to a usable outlet. Rock in the trench line, tight access between houses, and how much lawn, landscaping or paving has to be put back all affect the number. Two drains that look alike on paper can price differently for those reasons.

How long does a french drain last?

A well-built french drain lasts many years, and its life depends mainly on keeping silt and roots out. Filter fabric around the gravel, a sound outlet and keeping roof water out of the system make the biggest difference. A cleanout at the high end lets the pipe be flushed if it starts to slow down.

What is the difference between a french drain and a swale?

A swale is open: a shallow, grass-lined channel that carries surface water across the ground. A french drain is buried: a gravel trench with perforated pipe that collects water soaking through soggy soil. Swales handle runoff coming downhill, and french drains handle ground that stays wet. Many yards use both together.

Why does my yard stay soggy for days after it rains?

Usually because the water has nowhere to go. Clay soil drains slowly, a low spot with no outlet holds water, and ground compacted during construction sheds water poorly. A seep or high groundwater can also keep an area wet from below. Pinning down which one it is decides whether grading, a drain or both will help.

Should downspouts be tied into a french drain?

Usually not. A french drain is built to take groundwater slowly through its gravel, while a downspout dumps a large volume of roof water all at once, which can overwhelm the drain and push silt into the pipe. Roof water does better in its own solid pipe to an outlet, separate from the french drain.

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