Many yards have areas that collect water, a problem that a new patio or path can actually make worse. Water doesn't soak through the hard surface of a patio or path, so it runs into the yard. This runoff can create problems if you don't correct it before you start construction. Easy-to-install solutions can carry the water away.
A swale or French drain channels the water away from the site to a place where it won't cause problems. You can divert water only to another place on your own property, however, not to the neighbor's yard. If you can't divert the water to a good location, you'll have to run a French drain to a dry well.
A dry well collects water and lets it seep slowly into the surrounding soil. Look to local codes for the required dry-well size for your area. The size could be subject to conditions of your property or neighborhood. Even if your yard doesn't have runoff problems, you can avoid creating them by installing a gravel-lined trench around the patio.
Be sure to check the location of underground utility lines before you install any kind of drainage system.
Using a spade, slice the sod along the path of the line, about 2 feet wide. Remove the sod, roll it up, and save it. Dig out the trench about 6 inches deep all along the line, using a slope gauge to slope it 1/4 inch per foot. At the low end of the trench, dig a dry well about 2-4 feet wide and 3 feet deep. Line the trench with landscape fabric and gravel. Then lay in 4-inch perforated drainpipe with the holes facing down. Continue running pipe a few inches into the dry well. Connect the pipe sections with fittings and without glue.
To keep the gravel from settling into the soil, line the well with landscape fabric, leaving about 2 feet of surplus fabric on each side. Cut a hole for the drainpipe. Then fill the trench and the well with gravel, leaving enough clearance over the well for a 2- to 3-inch-thick patio block cover.
At the well, fold the surplus landscape fabric over the gravel and cover it with a patio block. Backfill the trench and the well, tamping the soil lightly.
Cover the patio block with at least 3 inches of soil, tamping it lightly with a garden rake. Then replace the sod.
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