Retaining walls are an aesthetically pleasing, yet functional, addition to any landscape. Retaining walls elevate herb gardens and flower beds, terrace steep lawns or provide additional usable (i.e., level) lawn space. However, seasonal rains can saturate the ground, and retaining walls block the natural flow of the water through the soil. As a result, the ground behind the wall becomes water-laden and soggy, and flooding of the lawn and even basements may occur. Design your own retaining wall drain to prevent or eliminate flooding problems.
Check the face of the retaining wall for weep holes -- spaces in the brick or rock left to allow water to seep through instead of backing up behind the wall. If there are no weep holes, drill a weep hole every 1 to 2 feet along the length of the wall, approximately 6 inches above the soil level.
Dig a drainage trench at least 2 inches wider and 6 inches deeper than the perforated drainage pipe. Dig a the trench along the entire length of the wall or only in areas that routinely flood, depending on the degree of flooding and the amount of drainage needed. In hard or rocky soils, use posthole diggers to dig individual drainage holes to the depth of the weep holes, immediately behind the wall.
Line the trench(es) or drainage holes with landscape filter fabric. Fill the trench or hole with gravel, cover with a layer of filter fabric and cover with at least 6 inches of fill dirt. Lay perforated pipe over an inch-thick base layer of gravel in trenches, if needed, to improve drainage.
Dig drainage holes in rocky soil with an auger, rather than by hand.
Be sure not to undermine the structure of high, load-bearing retaining walls.