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How to Drain Land

Updated February 21, 2017

Learning to drain soggy land is essential. Over-watered land can retard crop growth and cause soil erosion. With properly drained land, crops can increase by almost 30 per cent; while for grazing, there is less damage to the soil and cattle can graze up to three weeks more than with undrained land, according to Land Improvement Contractors of Ontario. There are two basic forms of draining: French draining and trench draining. Both have excellent records and work equally well. In general, the latter is good for backyards, while the former works best with agricultural fields.

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  1. For trench draining, dig a trench about two feet deep and six inches wide from the highest to the lowest part of the land. The slope need not be great--anything slightly more than perfectly flat is sufficient--but a 1-percent gradient is ideal. The bottom should be filled with gravel about two inches deep. It might be a good idea to line the trench with landscaping fabric to solidify the trench walls, though this is not necessary. Only the tiniest gradient in the land is necessary for efficient drainage, though occasionally pumps are necessary for absolutely flat land.

  2. Fit the drainage pipe into the trench by placing it in, and cover all remaining spaces with gravel. You can cover over the trench with grass if needed. The pipe should gradually emerge from the ground where it drains out. Deciding where the water drains can be a challenge. Usually the public sewer system is used or a local stream. Check local regulations before you decide.

  3. For French draining, dig trenches throughout the land about two feet deep and six inches wide from the highest to the lowest part of the land, which eventually empty out into a master drain. Each trench should drain a specific part of sodden land, but all should eventually connect into the single, master drain. Fill the trenches with gravel. There is no pipe in French draining, merely gravel to help move the water. The spacing of the trenches depends on the permeability of the soil. Low permeability can go as low as 50 feet between drains, while highly permeable soil can necessitate drains up to 300 feet apart.

  4. Make arrangements with a local contractor to have the drainage system, whether it be trench or French, inspected every fall and spring on a regular basis in order to protect your drainage investment.

  5. Tip

    For both styles of drain, the only real major issue is to figure out the slope of the land (if it is not obvious), and connect the single trench (for trench training) or the French-style multiple trenches to the lowest point in the land itself. A simple line level can be used here, where a string is connected to two poles and a level hung from the centre. Once this challenge has been mastered, it is just a matter of digging. For the pipe, larger openings might be necessary depending on how much silt might collect in the drainage water. The amounts here depend on the size of the project. It is best to ask a landscaping store how much gravel and pipe are necessary, given the length of your trenches. Some kinds of gravel have larger pellets, some smaller. Therefore, the calculations should be done on site rather than hypothetically.


    Make certain the area you live in does not have regulations for such drainage. Contact the local government office before you begin work.

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Things You'll Need

  • Shovel
  • Round gravel
  • Landscaping fabric (optional)
  • Plastic drainage pipe with a 4-inch diameter opening
  • Grass seed or sod (optional)

About the Author

Walter Johnson has more than 20 years experience as a professional writer. After serving in the United Stated Marine Corps for several years, he received his doctorate in history from the University of Nebraska. Focused on economic topics, Johnson reads Russian and has published in journals such as “The Salisbury Review,” "The Constantian" and “The Social Justice Review."

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