French Drains vs Swales: When Each Fixes Yard Drainage in Austin

TL;DR

On Central Texas lots, surface water problems are best solved with surface solutions. If rain visibly sheets or pools, start with regrading and a vegetated swale that carries flow at a 2–8% fall to a safe outfall. Use a French drain (perforated pipe in gravel with fabric) only when water is subsurface—springy clay seams, seepage against a wall, or a shaded low spot that never dries—even after you’ve built correct sheds. Good French drains need continuous slope (≥1%), a cleanout, and a clear daylight outlet; swales need mower-friendly side slopes (e.g., 4:1) and stable outfalls. Most Austin properties win with a hybrid: regrade and swale first, then add a targeted French drain where soils weep. If you want an Austin-first crew to walk the yard, laser-check slopes, and give you a line-item plan, you’re in the right place with Ace Excavating Austin.

Why Austin yards flood (and why “more pipe” isn’t always the answer)

Austin is a tale of two soils. West of MoPac, thin soils over limestone shed fast; east toward Elgin and Hutto, you’ll find expansive clays that swell wet and crack dry. Most “yard drainage” headaches start because finished grades don’t move water on purpose. The fix is to choreograph water with surface planes and carriers—not bury it and hope.

When a French drain is installed where a swale should be, it becomes a hidden pond: water collects in the trench, saturates clay, and slowly releases—sometimes back into your patio edge. That’s why we design the surface first, then add subsurface where soils leak from below.

Early in every project, we confirm:

• Is water arriving on top (roof, neighbor sheet flow, flat sod)? → Swale and regrade.
  
• Is water emerging from below (seep, perched water in clay, retaining-wall toe)? → Consider French drain—after sheds are correct.
  

Swales in Central Texas: shapes, slopes, and outfalls that work

A swale is a shallow, grassed channel that collects sheet flow and carries it to a safe outfall. Built right, it’s easy to mow, comfortable to walk, and nearly invisible.

Shapes and side slopes

• Depth: typically 3–8 inches for residential yards.
  
• Side slopes: 4:1 (4 feet run per 1 foot rise) or gentler—so wheels don’t scalp, and kids don’t trip.
  
• Bottom width: 18–36 inches for small carriers; go wider if you expect more flow.
  

Longitudinal slope

• Aim for a 2–8% fall. On clays, we avoid <2% because water lingers, promotes algae growth, and softens the subgrade. On long, gentle runs, 3–4% is the sweet spot.
  

Outfalls

• Preferred: tie into a street inlet or curb cut if allowed; otherwise, a stabilized daylight with riprap or a small energy dissipator.
  
• Never discharge at a fence post or neighbor’s line—shape to a lawful outlet.
  

Mower-friendly details

• Blend swale shoulders back into the lawn so the mower deck doesn’t scalp the shoulders.
  
• Keep side slopes consistent; avoid “speed bumps” that trap silt.
  

Why do swales win first?
They’re cheaper, faster, handle big storms, and keep water out of the soil rather than inviting it into a trench. And they complement your first 10–15 feet of shed away from the foundation.

If you want to see how we tie swales into broader grading work (pads, drives, proof-rolls) and inspections, our site preparation walkthrough shows the sequence we use to go from soggy yard to storm-ready grade.

French drains that actually drain: trench makeup, fabric, and outlets

A French drain collects subsurface water and moves it by gravity. It’s not a magic straw; it’s a miniature rock trench that needs open voids, clean pipe, and somewhere to go.

Trench recipe

• Trench width: 12–18 inches, typical for yards.
  
• Depth: to intercept seep (often 18–30 inches), staying above utilities and roots where possible.
  
• Fabric: non-woven geotextile lines trench to keep soil from fouling rock.
  
• Aggregate: clean, washed stone (e.g., 3/4″) from bottom to a few inches below grade.
  
• Pipe: Perforated SDR-35 or HDPE with sock (if fabric wrap is minimal), placed at the bottom third of the stone column.
  
• Slope: ≥1% continuous; more is better on short runs.
  
• Cleanouts: at direction changes and run ends—a vertical riser with a cap you can flush.
  
• Outlet: daylight to a curb cut or slope with a rodent screen, or tie to a legal storm structure.
  

What it is not

• It’s not a substitute for a swale, where water collects in sheets.
  
• It’s not a “drywell” in clay; clay doesn’t wick like sand.
  
• It’s not a flat pipe in mud. No slope = no drain.
  

When a French drain is justified (toe of a retaining wall, seep at the base of a hill, patio edge that stays soggy after regrading), we design the shortest, straightest run with the cleanest outlet.

How to choose: a simple decision tree for Austin soils

Start here: After a storm, do you see water on the surface?

• Yes, water sheets or ponds → Build sheds and a swale to a safe outfall.
  
  • After you regrade, does the area dry out within 24–48 hours?
    
    • Yes → You’re done.
      
    • No, ground still spongy (esp. on east-side clays, in shade, or at a hillside toe) → Add a targeted French drain to intercept seep beneath the corrected surface.
      
• No, lawn looks normal but stays wet at depth (footprints sink, wall base wicks) → This is subsurface water.
  
  • Confirm you have a legal outlet with continuous fall.
    
  • Install a French drain along the wet line, keeping fabric, stone, cleanouts, and slope to standard.
    
  • Still have surface inflow? Add a shallow swale above the line to keep new stormwater from re-wetting the route.
    

In short, Swale first for surface, French drain second for subsurface. Many yards need both, but only in the exact spots each is built to solve.

Hybrid designs: pairing sheds, swales, and selective subsurface drains

Most of our successful Austin yard rehabs follow a three-step blend:

1. Laser-check and correct sheds for the first 10–15 feet away from the house at a 1.5–2% fall.
   
2. Cut a grass swale at a 3–4% fall that ties sheds to a stabilized outfall.
   
3. If needed, add a French drain under the swale’s high side—or along a wall toe—only where seepage persists.
   

On west-side lots with limestone shelves, we rely more on controlled planes and outfalls than subsurface drains. On east-side clays, a short, well-built French drain along a perched seam can stop a chronic wet line after you get the surface right.

For slope targets, tolerances, and field workflow that make the hybrid work, our land grading overview lists the exact falls we build on clay and limestone, and how we verify them with the laser.

Specs and details: side slopes, pipe sizes, rock gradations, and cleanouts

Swale specs (residential)

• Side slope: 4:1 or gentler (mower-safe).
  
• Bottom width: 18–36″; wider if you need capacity without depth.
  
• Longitudinal slope: 2–8%; 3–4% is a reliable target on clay.
  
• Stabilization: Hydroseed or sod on clays; consider erosion mat on slopes >10%.
  

French drain specs (residential)

• Pipe: 4″ perforated for most yards; 6″ if long runs or higher flows.
  
• Stone: Clean, washed 3/4″; no fines. Fill to within 2–3″ of the finish grade.
  
• Fabric: Non-woven wrap around stone; lap seams 12–18″.
  
• Slope: ≥1%; we prefer 1.5–2% if space allows.
  
• Cleanouts: at each turn and near the high end; label caps discreetly in landscape.
  
• Outlet: Rodent screen and a lip you can see; never bury your only proof that the line works.
  

Outfall armor

• Small riprap or a splash pad where water daylights on clay to prevent scour.
  
• Hook silt fence around work areas during construction (toe 6–8″, posts upslope).
  

Tie-ins

• If your swale must pass under a fence, we either notch and armor the fence line or add a small culvert set on grade. Don’t let a fence become a dam.
  

Oak protection, safety, and erosion controls during work

We protect what you bought the property for:

• Tree protection zones (TPZ): fence to the dripline (or 1.5–2× DBH radius for big live oaks). No turning or staging in the TPZ.
  
• Crossing roots: If we must cross, we do it once, straight, on composite mats or geogrid + 4–6″ washed rock—no spinning tracks.
  
• Oak-wilt hygiene: Any fresh cut gets wound paint within 15 minutes, year-round. Saws are cleaned between trees.
  

BMPs day one

• Silt fence on downslope edges (toe 6–8″, posts upslope; hook ends).
  
• Stabilized construction entrance at the street (non-woven fabric + 2–3″ washed rock, 20–30′ long) so we don’t track fines.
  
• Wattles/checks on steeper slices every 30–60′ until grass takes.
  

Timelines, production, and what affects your budget

Typical production (weather cooperating)

• Laser layout + minor regrade around the house (first 10–15′): ½–1 day
  
• Cut and stabilize a 100–200′ swale: ½–1 day.
  
• Install a 60–120′ French drain with one outlet and cleanouts: ½–1 day
  

What moves the number

• Clays (need moisture conditioning, possibly erosion mat)
  
• Tight gates (6–8′ opening means smaller iron, more hours)
  
• Root zones (hand work around TPZs adds time)
  
• Outlet distance/elevation (daylight slope is king; longer runs cost more)
  
• Rock shelves (on west side, less trenching, more reliance on surface carriers)
  

If the yard fix is part of a broader project (pads, drives, access), we tie your drainage scope into a single line-item plan so you don’t pay to move the same soil twice.

To see how the drainage plan fits into your overall grading milestone, our plain-English primer, What Is Land Grading?, is a good mid-read reference.

Two example yard fixes

West Austin hillside (limestone shelf, heritage oaks)

• Symptoms: Splash lines on the foundation, muddy side yard after storms.
  
• Plan:
  
  • Fence TPZs at driplines.
    
  • Regrade first 10–12′ around the house at ~2% away from the slab.
    
  • Cut a 3–4% grass swale parallel to the house, blending into slope lines.
    
  • Daylight to curb via a stabilized outlet with a discreet rock pad.
    
  • No French drain: soil is shelf-like; surface carriers beat subsurface.
    
• Why it works: Moves water on top, preserves roots, and avoids cutting trenches into rock and lawn.
  

East Austin infill (expansive clay, shady side yard)

• Symptoms: Yard looks flat, dries slowly; patio edge stays spongy days after rain.
  
• Plan:
  
  • Correct first 10–15′ sheds at ~2%.
    
  • Cut a 3% grass swale to the street-side daylight with riprap.
    
  • Add a 90′ French drain under the fence-side planting bed where seep persists; non-woven fabric, 3/4″ stone, 4″ perforated at 1.5%, cleanouts at ends and the one turn, rodent-screened outlet.
    
• Why it works: Surface water leaves in hours; chronic seep is captured below without turning the whole yard into a gravel trench.
  

FAQs

What’s next

If your yard ponds after every storm—or stays soggy days later—we’ll walk it with you, set benchmarks, and give you a line-item plan with sheds, swale geometry, and (if needed) targeted French drains that actually slope and daylight. We’ll protect your oaks, keep the street clean, and leave you with slopes you can verify with a level. Ready for numbers and a date? Get a clear drainage & grading estimate, and we’ll lock a calendar window.