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Drainage is an effective means of sanitizing a regularly flooded or waterlogged terrain. Especially in the presence of clay or loam soils that retain moisture well. But drainage can not be improvised. Badly done, he will not fulfill his role. And it can destabilize the foundations of a building by changing the nature of the soil.

The functioning of a drainage

The purpose of drainage is to allow the evacuation, out of the ground, of excess water in the basement.

A drainage network consists of:

  • Drainage trenches regularly distributed on the ground.
  • At the bottom of the trenches is a PVC drainage pipe flexible covered with geotextile felt and gravel.
    It is a perforated pipe with a diameter of 50 to 80 mm. Its diameter depends directly on the amount of water to be evacuated.
  • Water flows to one or perforated manifolds larger diameter (80 to 100 mm).
  • It arrives in a cement look to be finally eliminated by a PVC evacuation pipe of at least 100 mm, to an outlet (ditch, public drainage system, sump).

For the water to flow properly, the drainage network must have a slight slope between 3 and 10 mm per meter.

How to drain a lot

Realizing the drainage of a land requires order and method!

  • Staking the ground: To achieve drainage, start by staking the ground to mark the location of the draining trenches.
    The closer the trenches are to each other, the more effective the drainage will be. On average, it is good to space them from 5 to 6 m.
  • Dig trenches: To dig trenches, depending on their depth and number, the moche or the mini excavator is needed... Do not forget to plan a slight slope.
    Their depth depends on the nature of the terrain. Ideally, you have to go for a permeable layer of soil. The depth also depends on the plants you will grow: For a lawn, a depth of 30 to 50 cm will be sufficient. For a pleasure garden or vegetable garden, go down to 50 or 80 cm. And for an orchard go from 80 cm to 1.50 m.
  • Install drains and collectors: It is necessary to install at the bottom of the trenches a bed of ten cm of pebbles of average grain size (20/40 or 30/60). Then deposit the drains and collectors in the trenches while checking the slope.
    In clay, loamy or sandy soils, it is good to take the precaution of surrounding pebbles, drains and geotextile collectors so that the holes are not clogged.
  • Cover drains: The drains must be covered with 20 to 30 cm of pebbles. Traditionally, the drains are covered with several layers of aggregates of different sizes: Average particle size around the drain (20/40 or 30/60), 10/20 gravel above and then 5/15 chippings. Finally the whole is covered with a layer of sand then earth or vice versa.

Remember to keep a plan of the drainage network to avoid damaging it when planting shrubs or trees or during new construction.

Learn more about: Earthworks.


Video Instruction: Draining a flooded wood