Slopes, red clay and runoff
Erosion control for sloped yards in Marietta, GA
If red clay washes across your driveway or patio after every storm, the slope is losing soil and the water has no controlled path. Erosion control in Cobb County usually means steering runoff with drains, swales and downspout lines, then holding the slope with low retaining walls, terraces and ground cover. Get a free written plan and price from a local crew.
Why it happens
Why Cobb County slopes wash out
Marietta sits on Georgia Piedmont clay and gets about 50 inches of rain a year. Clay soaks up water slowly, so heavy rain runs off the surface and takes soil with it. Slopes left bare after construction, shaded ground under mature trees where grass will not grow, and downspouts emptying onto a hill are the most common starting points.
Red clay streaks on hard surfaces
Mud fanning across the driveway, patio, sidewalk or street after a storm.
Rills, gullies and exposed roots
Small channels cutting down the slope, roots showing at the surface, mulch beds that empty out.
Undermined walls, fences and steps
Soil washing out at the base of a retaining wall, fence posts leaning, or gaps opening under walkways.
How it gets fixed
Control the water, then hold the soil
Most lasting fixes combine two or three of these. Fixing the soil without fixing the water only buys a season.
Downspout lines
Roof water piped underground to an outlet below the slope instead of pouring onto it.
Downspouts 02French drains and swales
A drain or grassed swale across the top of the slope catches runoff and carries it around the bare ground.
French drains 03Low walls and terraces
Block, stone or boulder walls break a steep slope into flatter steps that hold soil and plants.
Retaining wallsCover the ground
Plants suited to the sun or shade, mulch, or stone on the flatter areas so rain stops hitting bare clay.
Typical prices
What erosion control costs in Marietta
Erosion control is priced by the pieces the slope needs. These are typical installed ranges from published 2026 cost guides, not our quotes.
- Land gradingTypical project$900 to $3,000
- Grassed swalePer linear foot$5 to $15 / ft
- French drainPer linear foot, installed$20 to $50 / ft
- Underground downspoutOne extension$800 to $2,000
- Block retaining wallPer sq ft of wall face$30 to $90
- Natural stone wallPer sq ft of wall face$45 to $110
Sources: Angi retaining wall cost (2026); Angi yard drainage cost (2026); Angi underground gutter drainage cost (2026); LawnStarter retaining wall cost guide (2026). Typical ranges, not quotes.
Around Cobb County
Where erosion shows up most
Every lot is different, but the same patterns come up across the service area.
Acworth lake slopes. Rolling lots near Lake Acworth and Lake Allatoona, where bare clay on a slope washes quickly. See Acworth walls and drainage.
Kennesaw and Marietta hillsides. Steeper ground near Kennesaw Mountain sends a lot of runoff downhill onto patios and driveways. See Kennesaw.
East Cobb and Vinings wooded lots. Shade and roots leave slopes bare under the trees, and older timber walls often fail as the soil behind them washes out. See East Cobb.
New builds and graded lots. In Smyrna, Powder Springs and other areas with new construction, freshly graded slopes need cover and drainage before they settle in. See Smyrna.
Before work starts
Permits, creeks and neighbors
Under the rules for unincorporated Cobb County, a retaining wall over 4 feet tall, or one holding up a driveway, structure or slope, generally needs a building permit and plans stamped by a Georgia licensed professional engineer. Cities inside the county set their own rules. Work near a creek or lake can fall under stream buffer rules. Source: Cobb County residential permitting.
Runoff should be sent to an outlet on your own lot, a dry well, or an approved point, not concentrated onto a neighbor's yard. If soil is already washing out from under a wall, see retaining wall repair.
FAQ
Erosion control questions
What is the best way to stop erosion on a sloped yard in Marietta?
Control the water first, then hold the soil. That usually means piping downspouts away from the slope, catching runoff above it with a drain or swale, breaking up a steep grade with low walls or terraces, and covering bare clay with plants, mulch or stone. Grass alone rarely holds a steep, shaded clay slope.
Do retaining walls stop erosion?
They help when the slope is too steep to hold plants. A wall turns one long slope into shorter, flatter steps, so water slows down and soil stays put. The wall needs gravel backfill and a drain pipe behind it, or the same water that was eroding the slope will push the wall.
Why does red clay wash onto my driveway after every storm?
Bare clay sheds water fast, and each storm carries a little more of it downhill. The usual causes are downspouts dumping onto the slope, a yard that drains toward the driveway, or ground with no cover. Fixing where the water goes is what stops the streaks.
How much does erosion control cost?
It depends on the fix. As typical 2026 ranges: land grading about $900 to $3,000 and grassed swales about $5 to $15 per foot (Angi), French drains about $20 to $50 per foot (Angi), and block retaining walls about $30 to $90 per square foot of wall face (LawnStarter). A site visit decides which pieces you need.
Do I need a permit for erosion control work?
Planting and small drains usually do not. Walls over 4 feet, or walls holding up a driveway, building or slope, generally need a permit and engineered plans in unincorporated Cobb County. Work near a creek or lake can fall under stream buffer rules, and Lake Allatoona frontage can add Army Corps of Engineers rules. That is checked for your address.
Get a free erosion control quote
Send a photo of the slope and where the mud ends up. A local crew follows up with a written plan and price.