It’s important to dig a trench in such a way that water drains away from your home without causing damage to your yard or a neighbor’s property. Make sure your ground slopes naturally away from your home or grade your drainage ditch so that it descends 1 inch every 10 feet. Start the trench at a flooded area or near a downspout outlet. Terminate the drain at a safe place, where any water flowing out the end will not cause erosion.
Dig a trench that is 18 inches deep and 9–12 inches wide. Lay water-permeable landscaping fabric in the trench, followed by 3 inches of gravel. Lay your perforated drain pipe in the trench, cover with an additional 3 inches of gravel, and cover the drainage ditch with rocks, soil, or stones.
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10 Steps to Dig a Trench for Drainage
A flooded yard or garden is a disaster that drowns plant roots, causes rot, and can damage your home. In most cases, yard flooding is caused by improper drainage. As such, one of the best ways to dry up a wet yard is by digging a drainage ditch and installing a proper drain pipe.
Plan Before You Dig
Before you begin to dig your drainage trench, determine the following:
- Where is surface water collecting in your yard?
- Where is excess water coming from?
- Where can water be directed in such a way that it won’t damage your property or neighboring property?
Plan to direct the flow of water downhill, away from flooded areas. Although you can direct water through a solid pipe to a location away from your home, often the best solution is a french drain. A french drain is a perforated pipe that evenly distributes water underground as it travels away from the flooded area. When working properly, A french drain eliminates the water-spewing traditional pipe end, which can cause erosion.
Determine the Slope
For water to properly drain, your drainage trench must slope downwards at least 1 inch every 10 feet of length. To determine slope in your yard:
- Mark 2 wooden stakes at 1-inch intervals
- Drive stake A into the ground at the point where you wish to begin your drain.
- Drive stake B into the ground at the point where the drain will end.
- Tie a string between stake A and B.
- Use a level to make sure the string is level.
- Check the difference in height between where the string is tied on stake A and B. This is the amount of slope between the two points.
As long as the slope descends at least 1 inch every 10 feet of distance, water will naturally drain along a trench dug there. If your lawn is flat, you will need to compensate and create a slope. When you dig your trench, you will need to make it at least 1 inch deeper every 10 feet to create an artificial slope and induce drainage. If you do not have enough slope, the water will not drain through the pipe.
Dig your Trench
Use a tool designed for digging a trench to dig your trench. It’s important to create a large enough trench that you can fill it with gravel and accommodate an adequately-sized drainage pipe. Optimal trench dimensions are:
- Width: 9–12 inches
- Depth: 18 inches
- Remember: deepen your trench in direction you want water to travel when digging a trench on flat ground.
Make sure your trench follows a downward slope that carries water away from your home or any other buildings.
Lay Landscaping Fabric
Now that you’ve dug your trench, line it with water-permeable landscaping fabric. This will help prevent grass and plant roots from infiltrating your trench. Invasive roots can destroy drainage ditches, clog pipes, and undo your hard work.
It’s perfectly okay to have excess landscape fabric. I can be folded over gravel and covered in the following steps.
Pour a Gravel Base
Pour 3 inches of gravel into the bottom of your trench, on top of the landscape fabric liner. This is ideal when installing a french drain, because it allows water to filter out through the perforated pipe and filter into the soil. An adequate layer of gravel improves drainage. The simplest drains are just trenches filled with gravel.
Install Your Drain Grate
At the top of your trench, you will need to install a drain grate and outlet to allow water to enter the drain pipe and flow through your drainage trench. The two common areas to place your drain pipe are:
- Near a gutter downspout to direct rainwater into trench.
- In a flood-prone or wet area of yard to draw in water.
The goal of the drain is to receive the water that was previously flooding your yard and redirect it through the drainage trench. Begin your trench in the flooded area and plan to install your drain grate at the top of the slope.
Install Drain Pipe
Connect your drain pipe to the drain outlet and lay it on top of the gravel bed along the length of your drainage trench. The two types of pipes commonly used for drainage trenches are:
- Perforated Pipe: distributes water underground evenly along the length of the trench, eliminating a messy spout at the end of the drain.
- Solid Pipe: carries water to an unobstructed, open end. The spout should be positioned where it will not flood another area or a neighboring property. It should drain into a pond, bed of gravel, or a rain garden.
Make sure your pipe is solidly connected along its length and is well supported by the bed of gravel along the floor of the trench.
Cover Pipe with Gravel
Cover the drainage pipe with an additional 3 inches of gravel. This will protect the pipe and allow for adequate drainage from a perforated pipe in a french drain.
Fold Landscape Fabric Over Gravel
If you had excess landscape fabric following step 4, wrap or fold this landscape fabric over the gravel. This will create a tube of landscape fabric around the gravel and pipe, protecting it from invasive roots.
At this point, how you cover your trench is up to you. Some solutions are:
- Fill the trench with additional gravel.
- Line the trench with bricks or stones.
- Cover the trench with soil—you can even plant grass on top!
Many homeowners choose to fill the trench with gravel, allowing for simple repairs to the drainage pipe at a later date if necessary. However, a properly installed drainage trench will function for years, so feel free to cover your trench through permanent means if you like.
How Deep Should a Trench Drain Be?
A drainage trench should be at least 18 inches deep. This allows you to install a gravel bed, as well as an adequately-sized pipe to carry away water. It also allows you to cover the pipe to protect it and make your drainage trench an attractive lawn feature.
You will also need a wide trench to provide adequate room for your pipe and gravel. Ecavate so that your trench is 9–12 inches wide. Narrow trenches provide poor drainage. A wide trench is best.
What is the Best Size Drainage Pipe?
A 4-inch diameter pipe is the best size for drainage applications. A 4-inch perforated pipe is ideal for french drains, while a solid variety is suitable for standard drainage trenches.
Smaller pipes are prone to clogs due to rocks and organic material. A good drain grate will filter out all large debris and keep a 4-inch pipe clog-free.
Best Tool to Dig a Trench
A trenching shovel is the ideal tool for trench digging by hand. A pickaxe or mattock can also be useful.
If you are digging a very long trench or are battling stubborn or rocky ground, consider renting a trencher from your local home improvement store. These motorized tools can turn hours of hard digging into minutes of work.
Digging a Trench for Water Drainage
A drainage trench is often the most efficient and effective way to carry large amounts of water away from your home or muddy portions of your yard. In order to dig a drainage trench, follow these steps:
- Plan your drainage trench. Start at the problem area and direct the water away from your home.
- Measure your slope to ensure the ground falls at least 1 inch every 10 feet. If it doesn’t, plan to deepen your trench as you dig, to create an artificial slope to draw water away from the flooded area.
- Dig your trench. It should be 18 inches deep and 9–12 inches wide.
- Line your trench with water-permeable landscape fabric.
- Lay 3 inches of gravel in the bottom of the trench.
- Install a drain grate and outlet at the top of the trench.
- Install your drain pipe in the trench. Use perforated pipe for a french drain. Use solid pipe if you want to redirect the water to a pond or rain garden.
- Cover the drain pipe in gravel. Bury it at least 3 inches.
- Wrap any excess landscape fabric around the gravel to protect the pipe from invasive plant roots.
- Cover the trench with coarse gravel, stones, pavers, or soil.
By following these steps, you can create a durable, clog-resistant drainage trench that reduces yard flooding, protects your home and plants, and will remain in use for many years to come.