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Dry Well vs French Drain: What’s the Difference?

Dry wells and French drains are very different forms of drainage control and can be used in combination with one another. A dry well is a covered hole filled with gravel or similar material. It serves as an endpoint for your drainage system. Water is directed to the dry well, where it filters down through the gravel and is distributed deep into the soil. A French drain is a type of drainage trench that collects water and directs it downhill. A French drain needs a termination point to release all of the water it collects. A dry well is a great termination point for your French drain.

Dry well vs French drain

What is the Purpose of a Dry Well?

A dry well is designed to receive water from a drainage system and disperse it below ground. All drainage systems have to end somewhere. If you can’t drain your water into a storm drain or don’t want to direct runoff into a pond or water garden, a dry well is the perfect choice. Think of it as a method for taking runoff water and filtering it into the soil deep beneath the surface of your yard.

  • A dry well receives water from a drainage system, such as gutter downspouts, drainage ditches, or a French drain.
  • Dry wells receive runoff water from a drainage system and distribute the water underground.
  • Dry wells do not do well at collecting runoff on their own—a drainage pipe or system must direct water to the dry well.
  • A dry well eliminates the need for terminating a drain aboveground, where drain water can cause flooding and erosion.

In many regions, it’s illegal or impractical to channel runoff water into municipal storm drains. Rather than channeling the water from your downspouts out into your yard, where they can flood your lawn, a dry well allows you to get rid of that water underground.

Do Dry Wells Really Work?

Dry wells are tried and tested technology. An adequately sized dry well in soil that percolates well can get rid of a large volume of water below ground without causing any soggy areas in your yard.

  • Dry wells have been used successfully for hundreds of years.
  • Simple dry wells lined with landscape fabric and filled with gravel can be effective. Use this dry well tank for even better drainage.
  • For best results, dry wells should be constructed in soil that absorbs water. They perform well in sandy and loamy soils but do poorly in heavy clay.

It’s critical to perform a percolation test before installing a dry well. Dig a hole, fill it with water, and see how quickly the water is absorbed. If you have heavy clay soil that does not absorb water, a dry well isn’t right for your yard.

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09/16/2021 12:06 am GMT

Does a Dry Well Need to be Pumped?

A dry well does not need to be pumped or emptied. It’s not a solid tank that fills up and requires emptying. Remember, the simplest dry wells are just a hole in the ground filled with large gravel. This gravel material helps the hole retain its shape and allows the water to filter down into the dry well, where it will then leach into the surrounding soil as groundwater.

What is the Purpose of a French Drain?

A French drain is a drainage system designed to gather rain and flood water from a large area and conduct it downhill. Unlike a typical solid drain pipe that transports water from point A (such as a gutter downspout) to Point B (a dry well), a French drain contains a perforated pipe. Because of the holes in the drain pipe, water that enters the drainage trench percolates up, enters the holes in pipe, and then is carried downhill.

  • French drains collect water over a large area, such as a hillside, and channel it through a perforated pipe to an endpoint.
  • French drains do well at collecting water that is infiltrating your home or flooding your driveway. It transports this excess water down a slope to a termination point.
  • A French drain requires a termination point to release water and prevent flooding the drainage trench.

A French drain cannot function alone. Because it gathers water and transports it down a slope, it requires an outlet where you can release the water.

Where Do You End a French Drain?

A French drain outlet can drain into a water garden, pond, stormwater system, or dry well. Before you decide where to terminate your French drain, check local building codes. In some areas, directing runoff water into a storm drain is illegal, and some regions place restrictions on dry well construction.

  • Terminate your French drain at a dry well, pond, water garden, or storm drain.
  • A French drain must have an outlet to prevent flooding.
  • Check local laws before terminating your French drain—there may be construction restrictions.
  • Never position a French drain outlet in such a way that it drains onto neighboring property. This is illegal. It’s your responsibility to deal with the water that collects on your property.

Remember, it’s essential to deal with the runoff water collected by your drainage system responsibly. A dry well makes for a great termination for a French drain because it empties runoff underground, where it cannot cause flooding or provide a breeding ground for insects.

How to Use a Dry Well and French Drain Together

French drains and dry wells work hand-in-hand. The French drain collects water and the dry well receives the water, so it can be safely dispersed beneath the surface of your yard. To employ these methods yourself, do the following:

  • Dig a drainage trench with 1–2 inches of slope for every 10 feet.
  • Install a French drain in the drainage trench, using landscape fabric, gravel, and perforated pipe.
  • Where the drainage trench ends, dig a dry well.
  • A dry well can be a hole 3 feet in diameter and 3 feet deep.
  • Fill the hole with landscape gravel or install this dry well tank and surround it on all sides (including the bottom) with landscape gravel.
  • Direct the end of the drainpipe into the center of the dry well.
  • Cover the dry well with turf or a grate.

It really is that simple. In soil that does not contain heavy clay content, the runoff water directed to the dry well will quickly percolate into the soil as groundwater. The chances of overflowing a properly installed dry well are very slim.

How Far Should a Dry Well Be From the House?

Dig your dry well at least 12 feet from the foundation of your home, garage, or other structure with a concrete foundation. This allows the dry well to disperse water below ground without any fear of causing wet soil near your home. It will also prevent basement leaks.

Will a Dry Well Work in Clay Soil?

Dry wells are not effective drain termination points in heavy clay soil. Clay soil absorbs water slowly, so water piped into the dry well will not naturally percolate. During heavy rain, a dry well constructed in clay soil will flood and leave the area around it a soggy mess. If you are concerned about the performance of a dry well in your yard, have a soil percolation test performed in your yard to determine if it will absorb water quickly enough.

French Drain or Dry Well?

French drains and dry wells perform different functions and work well together. A French drain is a pipe drainage system that collects runoff water from a wide area and channels it to a single point. However, it doesn’t disperse the water safely into the soil. A dry well serves as a great endpoint for drainage systems because it handles large volumes of water and disperses it underground. To be effective, a dry well should be the endpoint of a drainage system. You can direct your French drain to end at a dry well.

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