Retaining wall drainage and runoff fixes
It doesn't rain often here, but when it does it comes all at once. Make sure that water has somewhere to go besides behind your wall.
Retaining wall drainage keeps water from building up in the soil behind a wall, where it adds pressure, softens the ground under the footing and pushes salts through the block. In Washington County, the risk comes in bursts: summer monsoon storms and the occasional heavy winter rain can dump a lot of water in a short time, and irrigation can keep soil behind a wall wet all year.
How does wall drainage work?
- Drain rock. Clean gravel directly behind the wall lets water drop instead of pushing on the block.
- Weep holes or a perforated pipe. Let collected water out through or under the wall.
- An outlet. The water has to go somewhere: to daylight, the street gutter where allowed, or another approved spot.
- Filter fabric. Keeps fine soil and blowsand from clogging the drain rock.
- Surface grading. Sends runoff away from the top of the wall instead of over or behind it.
What are the signs of a drainage problem?
- White crust or staining on the wall face
- Damp spots or water seeping through after irrigation
- Weep holes that never drain, or are plugged with soil
- Muddy washouts at the base after a storm
- A wall starting to lean after heavy rain
Can sprinklers damage a retaining wall?
Yes. Drip lines, sprinkler heads and lawn right behind a retaining wall keep the soil wet, which adds pressure and can move soils that react to water. Leaking lines are a common cause of wall problems in desert yards. Keeping irrigation away from the back of the wall, or switching to low-water landscaping near it, helps.
Where can the water go?
Water has to leave your lot without flooding a neighbor's yard or undermining their wall. On many St. George lots, the yard drains toward the street or a drainage easement. The City of St. George asks for a drainage plan with retaining wall permits, and a builder can suggest options that fit your lot and the city's rules.
What affects the cost of drainage work?
- New wall or existing wall. Retrofitting drainage behind a finished wall usually means digging behind it.
- Length of the run. Longer walls and longer outlet runs take more material.
- Obstacles. Pools, patios, landscaping and utilities in the way.
- Grading. Reshaping the yard to steer runoff.
Prices come from the builder after they've seen the site. We don't quote prices ourselves, and a phone estimate is only a starting point for a wall.
Where we connect you with help
Common questions
Can drainage be added to an existing retaining wall?
Sometimes, by digging behind the wall to add drain rock and pipe, or by drilling weep holes where the design allows. If the wall is already leaning, rebuilding that section with drainage may be the better fix.
Do block walls need weep holes?
Retaining walls usually need a way for water to escape, through weep holes, a drain pipe or both. Privacy walls on level ground generally don't.
Related services
More background: St. George retaining wall and block wall guide.
Block wall leaning or cracking?
A wall that's moving can fall without much warning. Keep kids, pets and cars clear and call to get it looked at.