In order to add a drainage trench to a gravel driveway you should:
- Plan your trench so that it eliminates standing water on your driveway.
- Dig the trench by hand or with a walk-behind trencher.
- Slope your trench downward to conduct water where you want it to go.
- Add a layer of landscape fabric to the trench.
- Pour 3 inches of coarse gravel into the bottom of the trench.
- Install a 4-inch perforated french drain pipe in the trench.
- Add more gravel around the pipe.
- Wrap excess landscape fabric around the pipe and gravel.
- Pour gravel on top to keep the landscape fabric in place.
- Test your trench to make sure it drains properly.
French drain systems, like this one, will collect standing water from sections of your driveway and conduct it safely downhill to a storm drain or underground dry well.
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Can a Trencher Cut Through a Gravel Driveway?
A high-quality trencher will easily be able to dig a trench in a gravel driveway. A walk-behind model can be rented here. These walk-behind trenchers are ideal for most yards and driveways. They can eliminate the backbreaking work of digging a trench by hand.
- A walk-behind trencher is adequate for digging a drainage trench in most gravel driveways.
- If your gravel driveway is extremely hard-packed due to industrial vehicle traffic, a ride-on trencher may be necessary to dig a trench through gravel.
If you are digging an extremely long trench (200 feet or longer) on hard-packed gravel, consider renting a ride-on trencher. These units will cut a trench through nearly any material except solid concrete or stone. No matter the gravel driveway, there is a trencher that can do the job.
How Do You Dig Up a Compacted Gravel Driveway?
You can use hand tools such as a pick, mattock, and shovel to dig a trench in a gravel driveway. However, if you are digging through very compacted gravel, this work can progress slowly. You can make hand-removal of gravel easier by watering the driveway daily for 5–7 days before you begin digging.
- Hand tools such as a mattock, pick, and shovel can be used to dig through compacted gravel.
- Watering a gravel driveway for several days prior to digging can help loosen the compacted rocks.
- Rent a walk-behind trencher to dig a trench in most gravel driveways.
A walk-behind trencher rented from a reputable tool company is the best way to dig a trench in most driveways. It will dig through gravel much more quickly than hand tools and produce a perfect trench a few inches wide. You can also use the trencher controls to precisely control trench depth and slope.
10 Steps to Dig a Trench in a Gravel Driveway
Digging a drainage trench in a gravel driveway requires proper planning. When done correctly, the drainage trench will be invisible, but it will work to drain standing water from your driveway, leaving a dry and usable surface.
Plan Your Trench
When planning your trench, locate the area where the most water stands in your driveway. Then, mark a straight line across your driveway at this point. This is where the horizontal trench will cross your driveway. Tie a string between two stakes across your driveway. This will give you a straight line to follow as you dig your horizontal trench.
- You will need to plan an L-shaped drainage trench for your driveway.
- Plan a horizontal trench cutting across your driveway at the point where water collects.
- Mark a vertical leg of the trench that runs downhill to a drainage area.
- This L-shaped trench will drain standing water off your driveway and carry it downhill.
The next step in planning is to make your trench into a L-shape. On one side of the driveway, plan a trench that runs from the horizontal trench downhill alongside your driveway. This trench should end at a drainage point or a dry well.
Dig the Trench
Using hand tools or a trencher, dig your L-shaped trench. It should be 12 inches wide (30 cm) and 18 inches deep (46 cm). Before digging, lay tarps alongside the trench. As you dig, pile the gravel and dirt onto the tarp. Some of this material can be used to fill the trench later.
- Dig a trench 12 inches wide and 18 inches deep.
- Dig a trench for the entire L-shape you marked in step 1. You need the trench across the driveway, as well as the one going downhill alongside it.
- Do not dig a shallow or narrow trench—this will result in poor drainage.
It’s okay if the trench is a little wider or deeper than the dimensions above. However, don’t dig a narrow or shallow trench. This can result in poor drainage, damage to the drain pipe, or simply not give you enough space for later gravel and pipe installation steps.
Slope Your Trench
To ensure proper drainage, slope your trench 2 inches downward for every 10 feet of length. Slope the trench in the direction you want water to drain. So, the short leg of the L that cuts across the driveway should slope down to the side of the driveway where the long arm of the L runs downhill. Similarly, the trench alongside the driveway should slope downwards toward the drainage point.
- Slope your trench downward 2 inches for every 10 feet of length.
- Slope the trench that cuts across the driveway so that water flows toward the trench alongside the driveway.
- Slope the portion of trench along the driveway so that water flows downhill.
To measure the slope of your trench, mark 2 stakes at 1-inch intervals, like rulers. Drive both stakes 12 inches into the ground at the bottom of the trench 10 feet apart. Then, tie a level string between the stakes. The string should be tied at a point 2 inches higher on the “lower” stake due to the slope.
Lay Landscape Fabric
Once your trench has been dug, lay landscape fabric in the trench. The fabric should cover the bottom of the trench, come up the sides, and out of the trench on either side. In future steps, you will wrap the landscape fabric around gravel and the drain pipe.
- Line the bottom and sides of the trench with landscape fabric.
- Allow extra landscape fabric to fold onto the ground on either side of the trench.
- In later steps, you will fold excess landscape fabric over the drain pipe and first layers of gravel.
Using landscape fabric is essential because it prevents dirt from being carried with runoff water. By filtering out dirt and mud, the fabric will prevent drain pipe clogs and backups. Without landscape fabric, the gravel and drain pipe will become filled with mud and dirt.
Add a Gravel Base
Pour gravel into your trench to create a 3-inch deep layer of coarse gravel at the bottom of the trench. The best gravel for drainage is #3 or #57 crushed stone. This gravel is large and angular enough that it allows for good drainage. Small gravel or pea gravel will inhibit drainage.
- Add 3 inches of gravel to the bottom of the trench, on top of the landscape fabric.
- Use #3 or #57 gravel for this task.
- Maintain the downward slope of both legs of the L-shaped trench, even when you add gravel.
Spread the gravel evenly throughout the bottom of the trench. It’s essential that you maintain the slope of the trench even when you add gravel. Do not create a level gravel layer that ruins the slope. This will inhibit drainage.
Install a Perforated Pipe
Lay a perforated pipe, like this one, in your trench. A 4-inch diameter pipe is best for this. Position the pipe so that perforations are low on each side. This allows water that usually pools on the driveway to filter into the trench, enter the pipe through the perforations, and then be carried downhill by your sloped trench.
- Lay a perforated pipe in the section of trench that crosses the driveway.
- Install a perforated or non-perforated pipe in the section of trench that runs alongside the driveway.
- Connect the two sections of pipe with an elbow fitting.
It is essential to use a perforated pipe for the section of trench that cuts across your driveway. If you wish, you can use solid pipe for the section of trench that runs downhill alongside your driveway. Connect the two pipes at the bend in the L by using an elbow fitting for your pipe.
Cover the Pipe with Gravel
With the pipe in place, add more #3 or #57 crushed stone around the sides of the pipe. Then cover the pipe with 2–3 inches of gravel. Do this for the section of pipe that crosses your driveway and the section that runs alongside the driveway.
- Pour additional gravel in the trench to cover the lengths of pipe.
- Cover the pipe with 2–3 inches of gravel.
- Do NOT completely fill the trench with gravel at this point.
You will not fill the trench completely during this step. There should still be a few inches between the top of the gravel and the top of the trench. This is okay at this point.
Wrap the Pipe and Gravel in Landscape Fabric
Wrap the excess landscape fabric around the pipe and gravel you have installed. By wrapping the pipe in fabric you create a filter around your pipe that will prevent dirt from clogging the gravel and the pipe itself.
- Fold the landscape fabric around the pipe and gravel you have installed.
- This creates a protective filter that prevents drainage pipe clogs.
Folding the landscape fabric over top of the gravel is all that’s necessary. You do not need to secure it in any special manner.
Bury the Pipe
With the landscape fabric in place, add additional gravel until the trench is filled and level with its surroundings. This final layer of gravel will keep the fabric in place.
- Top off the trench with gravel until it is level.
- If desired, use old gravel so that the trench blends in with the surrounding gravel driveway.
Although you can use old gravel you excavated in Step 2, it’s best to use clean, new gravel. It will allow better drainage if you use new gravel that is free from dirt.
Test your Drainage
With your drain pipe installed, use a hose or sprinkler to soak the driveway for 5–10 minutes. Check the performance of your trench. If it is working, you should see any standing water disappear from the surface of the driveway. It will then be conducted down to the end of the trench that runs alongside your driveway.
- Use a hose to water your driveway for a few minutes.
- Water should flow down your trench to the endpoint.
- End your drain pipe at a location where water can safely drain away.
It’s important to terminate your drain in the right location. You can have a driveway drainage trench empty into a storm drain or gutter, if this is legal in your area. Or, you can combine your french drain with a dry well to disperse the water underground.
How Do You Install a Trench Drain in a Gravel Driveway?
To install a trench drainage system in a gravel driveway, first plan and excavate a trench that will carry water off your driveway and downhill. To make digging a trench easier, use a walk-behind trencher that will dig up compacted gravel with ease. Then, install a perforated drain pipe surrounded by gravel and wrapped in landscape fabric. Once this has been laid in the trench, top it off with gravel. Just make certain that your drain is properly sloped to conduct water in the proper direction and provide a safe endpoint for the drain, so the water will not cause flooding elsewhere.