How to Tell if French Drain is Working [4 Signs of a Clogged Drain]

To determine if your French drain is working properly, look for signs of basement leaks or standing water in areas that are typically drained. For a closer look, remove some of the gravel that your French drain is buried in. If there is standing water visible in the drainage ditch, your French drain is not working properly. A good test of functionality is to uncover your French drain’s termination point to see if water is exiting the drainpipe as intended.

How to tell if french drain is working

4 Ways to Check if Your French Drain is Working

A clogged French drain will not direct water away from your home. The excess water can lead to flooding, leaks, and damage to your property. If you suspect your French drain has a clog, check for the following indicators:

Look for Standing Water

French drains are designed to collect rainwater and channel it downhill. If surface water is standing in low areas of the yard that are supposed to flow into your French drain, you have a drainage problem. If the low areas of your yard are as firm and dry as higher spots, then your French drain is working as expected.

  • Inspect low areas of your yard that are supposed to flow toward the French drain.
  • If the ground is flooded, boggy, or squishy, your French drain is not working.
  • A properly working French drain should keep low ground as well-drained as higher portions of the yard.

Excessive standing water or marshy soil is the first warning sign to check for when inspecting the health of your French drain. If you see this, look for the following signs of a non-functioning drainage system.

Check for Basement Flooding

In many cases, French drains are installed around foundations to prevent water from flooding the basement. If your basement walls are leaking, or if you see signs of mold and mildew in your basement, there’s a good chance your French drain isn’t working properly.

  • Check your basement for leaks, wet walls, moisture, mildew, and mold.
  • Water infiltration in the basement is a sign that your French drain isn’t working.

If your French drain isn’t positioned to protect your basement, or if your home doesn’t have a basement, ignore this step and proceed to physically checking the condition of your drain.

Inspect the Water Level in Your Drainage Trench

To see if your French drain is working properly, pick a section of your drain and use a shovel or trowel to remove the gravel in your drainage trench until you can see the drain pipe. Is there standing water in the drainage trench that has not been drained away? Is the water flooding over the top of the drainage pipe? If so, then your French drain is not working.

  • Use a shovel to remove the gravel from a section of the drainpipe. Be careful not to damage the pipe or any landscape fabric wrapped around it.
  • Inspect the drain pipe and surrounding gravel.
  • If water is standing in the drainage ditch or is coming up over the top of the drainpipe, the drain is not functioning.
  • If gravel is relatively dry and there is no standing water in the drainage ditch then your French drain is working as intended.

A French drain is a perforated pipe surrounded by gravel. As the floodwater flows into the trench, it filters up through the gravel and enters the holes on the bottom of the pipe. The water is then conducted downhill through the drain. If your drainage trench is overflowing or full, then the drain isn’t working. This could be due to clogged holes in the French drainpipe. A clog can be caused by tree roots or sediment.

Check the Drain Termination Point

One of the best ways to see if your French drain is working is to see if water that flows into the drainage ditch flows out the end of the pipe. To do this:

  • Find the downhill termination point for your drain. This could be a dry well or pipe end that directs water into a gutter.
  • Uncover the termination point if it is below ground level.
  • Use a garden hose to direct water into the drainage ditch 10–20 feet (3–6 meters) uphill from the termination point.
  • Allow 1–2 minutes for the water level in the trench to rise and enter the drain pipe.
  • If water begins to flow out of the pipe end, the French drain is working.
  • If water does not flow out of the pipe end, the French drain is clogged.

This simple test allows you to gauge the health of your drain. You can perform this check with just a few minutes of work.

How to Fix a Clogged French Drain

A nonfunctional French drain is often caused by dirt and debris clogging the perforations in the drain pipe. This prevents the water that flows into the drainage trench from entering the pipe and being funneled downhill. A properly installed French drain resists this type of blockage and requires little maintenance, but clogs can occur. To fix a French drain that isn’t working.

  • Excavate the top end of the drainpipe (the uphill end).
  • Remove any filter or cover from the French drainpipe.
  • Use a high-pressure hose sprayer to send a large volume of water into the drainpipe.
  • For added power, use a pressure washer to clear clogs.
  • If the drain still appears clogged, use a plumbing snake to remove clogs.
  • Continue these methods until water runs freely out of the downhill pipe end.

If your French drain is still not functioning properly after performing these steps, more drastic measures must be taken. A clogged French drain is usually caused by improper installation and poor base materials. To repair a chronically clogged French drain, you may need to excavate the drain pipe and reinstall it with proper gravel and landscape fabric.

How Do You Tell if a French Drain is Clogged

If you suspect that your French drain is clogged, look for the following signs:

  • Standing water in a low-lying area of your lawn where water should flow to the French drain.
  • Basement leaks of flooding. This can be seen by moisture coming through the wall after heavy rain, drips, mold, or mildew.
  • Remove the gravel covering a portion of the pipe in your French drain. If water is standing in the trench, the drain is clogged.
  • Uncover the termination point of your drain pipe. Direct water into the drainage trench 10–20 feet up the slope from the end. If water does not flow out of the pipe within 1–2 minutes, it is clogged.

A nonfunctioning French drain may be cleared with a pressure washer or by snaking the drain pipe. However, if a French drain becomes clogged on a regular basis, this is most likely due to improper installation. In some cases, the French drain must be reinstalled with special attention paid to using the proper materials and ensuring adequate slope to correct drainage issues.

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