How to Build a Retaining Wall to Address Drainage Problems on a Slope

Mark the location in front of the sloped area that has the worst drainage problem with wood stakes. Dig a trench along this area, using a shovel. Make the trench approximately 12-inches wide and at least 6-inches deeper than the height of the retaining wall blocks you will use.

Lay a 4-foot level in the trench. Dig dirt away from any high areas until your trench is level. Use a hand tamper to compact the dirt inside the trench. Check the trench for level once more. Add dirt back to any low areas and tamp them down.

Pour gravel into the trench. Use a metal rake to smooth the gravel into a 6-inch deep layer. Lay the 4-foot level on the gravel and use the rake to adjust the gravel so the level sits flat. Tamp down the gravel with a hand tamper. Spread a 1-inch layer of leveling sand over the gravel.

Start at one of the retaining wall's ends and lay the first block into the trench. Set a torpedo level on the block and check that the block is level from side to side as well as from front to back. Tap the block's high end with a rubber mallet to sink it into the leveling sand so the block sits flat.

Set another retaining wall block next to the first block, so they touch each other. Use the torpedo level to adjust the second block. Place a third block next to the second block and check this block for levelness. Lay a 4-foot level over the top of all three blocks. Add leveling sand under any low areas and then use the torpedo level to readjust each block as necessary.

Continue to lay three blocks at a time, checking each one for levelness and then checking them as a group. Once you have laid the first block level, begin with the second block level. Most retaining wall blocks have a lip on the back edge which butts up tight against the back edge of the block beneath it. Stagger the blocks' meeting joints to achieve a stronger retaining wall. Build the third block level on top of the second.

Add gravel behind one end of the retaining wall to create an even downward slope. The end you choose depends on where you wish water to drain to. For example, do not add gravel so water will drain toward your home as then you will probably be left with a drainage problem in front of your house. Instead, slope the gravel toward a driveway or sidewalk where water can easily run off into a storm drain.

Lay a perforated PVC drain pipe behind the retaining wall on the sloped gravel. Extend the end of the pipe resting on the low end of the slope 2 to 3 inches past the retaining wall.

Cut a piece of landscape fabric long enough and wide enough to cover the drain pipe. Lay the fabric over the drain pipe and pour approximately 6 inches of gravel on top of it. Continue building up your retaining wall until it reaches your desired height. Pour soil on top of the gravel, behind the retaining wall, as a back fill.