Creating A Lush and Welcoming Landscape

Block retaining walls are an excellent option for preventing slope erosion and developing your landscaping. Drainage can be an issue, though, so it's important to understand the basics.

Moisture Sources

There are several sources of moisture around a retaining wall. The sources of primary concern are those that originate behind the retaining wall. These will generally be from irrigation, rainfall, or snowmelt, although some natural moisture in the soil can also be a challenge. In many cases, moisture buildup behind a retaining wall is periodic—it may only occur seasonally when the snow melts off the slope, or it may be a daily occurrence for an hour or so as irrigation runoff travels down the slope.

Moisture beneath the wall is more rarely a concern, but it can be in certain conditions. A high water table combined with a high movement serpentine soil is damaging to retaining wall foundations, for example. A high frost line, which indicates the depth of average soil moisture freeze, can also impact a block wall. Generally, the answer to these issues isn't drainage-related, though.

Drainage Concerns

When water trapped behind the retaining wall can't drain properly, it puts hydrostatic pressure against the blocks. This pressure can cause the wall to bow outward and eventually collapse. Matters are made worse due to seepage between the blocks, particularly on dry fit walls, as this will erode the blocks and cause the wall to lose integrity more quickly. The slope the wall is meant to anchor will also begin to slump, which can lead to a total slope and wall collapse.

Some water may also collect under the wall, which can exacerbate water table issues and cause the foundation of the wall to shift. In winter, this water can freeze and expand, leading to ground upheaval that affects the retaining wall.

Management Options

Fortunately, almost all drainage issues can be mitigated during the installation of the block wall. The ideal retaining wall has a layer of gravel behind it. Multiple drainage pipes are also installed in the lower part of the wall's face.  Water flows down the slope, percolates through the gravel layer, then drains harmlessly out of the pipes.

A second buried perforated drain pipe is often installed at the base of the wall. This routes away the water draining through the retaining wall pipes away from the foundation so that water issues won't erode the soil in front of the wall.

Contact a retaining wall fence contractor like Quality Lawn & Landscape for more help with designing your wall.