How to Add Drainage to a Yard
If your yard is too wet you have a problem. Most plants will not thrive when their roots are struggling to grow in wet soil. Plants need water but they also need oxygen, and a soil that stays wet will not hold enough air to support good plant growth. You can correct this problem by adding drainage to your yard. This will allow excess water to drain away and dry out the first few inches of the topsoil, which is the root zone. Does this Spark an idea?
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Instructions
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Determine the slope in and around your yard. If there is water flowing into your yard from an uphill area, you might be able to solve the problem by installing a curtain drain to intercept that flow and redirect it. If there is no uphill area above your yard, you still need to determine the slope in order to know the direction to run your outfall drain.
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Make note of the areas where water pools in your yard after a heavy rain. Chances are that if you can drain that area you will effectively drain the entire yard. You don't want to do more work than necessary, so start with either a curtain drain (if water is flowing into your yard from uphill) or a French drain at the place or places where water pools. You want a curtain drain to run straight across the uphill end of your yard (to collect the incoming flow) and then down the slope to an outfall (to direct the water away from your yard). A French drain will run from the pooling area out to an outfall, which should be at the lower edge of your yard.
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Dig trenches for the drains approximately 10 inches wide and one foot deep. Into the bottom of the trenches lay about 2 inches of sand, then lay perforated plastic drain pipe on top of that. To ensure a good flow, you want the pipe to fall at least one to two inches every 8 feet, an incline of 1 to 2 percent. Check this with the spirit level and adjust the depth of sand in the bottom of the trench to keep the pipe consistently falling along its length.
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Lay landscape fabric over the top of the pipe. This will prevent dirt and plant material from clogging up the pipe. If you want to be really safe, you can wrap the pipe completely with the landscape fabric before you place it in the trench.
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Refill the trenches starting with drain rock: clean, round stones one to three inches in diameter. This material will allow the surface water to percolate through to the drain pipe. Refill with drain rock to within six inches of grade level and then use sand or topsoil to finish filling the trenches.
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Tips & Warnings
A less-expensive approach would be to eliminate the perforated drain pipe and just use drain rock in its place. This technique won't be quite as effective but could be sufficient to drain a yard with a minor drainage problem. You can still use landscape fabric over the drain rock to reduce the risk of clogging the drain.
Sometimes poor drainage is due to a high clay content in the soil. This can be relieved by the addition of organic material, such as compost, or even just grass clippings and the dead leaves of deciduous trees. You will need to add this material regularly over a long time, but it will eventually improve both the soil structure and the drainage.
Your first attempt at putting in drainage might not completely solve the problem. Pay attention to your yard the next time there is a heavy rain. If there is water draining out of the outfall you have certainly improved the situation, even if you have not completely solved the problem. If you are still seeing standing water 24 hours after the rain has stopped you will need to add more drainage.
