When homeowners call about drainage problems, they often use "French drain" and "surface drain" interchangeably. But these are completely different systems that solve different problems. Understanding the difference can save you from installing the wrong solution.
📷 Photo: Side-by-side French drain trench and catch basin grate
The Fundamental Difference
Here's the simplest way to understand it:
- Surface Drains collect water that's on TOP of the ground (rain, irrigation, melting snow).
- French Drains collect water that's BELOW the ground (groundwater, saturated soil).
If you install a French drain when you need a surface drain (or vice versa), you'll still have a water problem.
Surface Drains (Catch Basins) Explained
What They Are
A surface drain is a grated box (typically 6x6" to 12x12") installed at a low point in your yard. Water flows across the surface, falls through the grate, and is carried away by a solid pipe to a discharge point.
How They Work
- Water pools at the surface during rain or irrigation
- Gravity pulls water toward the catch basin (lowest point)
- Water enters through the grate
- A solid PVC pipe carries water to street, storm drain, or dry well
When You Need Surface Drains
- Puddles form during rain and stay for hours/days
- Downspouts dump water that pools against the foundation
- Patio or driveway low spots collect water
- Over-spray from sprinklers floods certain areas
- Neighbor's driveway drains onto your property
French Drains Explained
What They Are
A French drain is an underground trench filled with gravel and a perforated pipe. It collects water that has already soaked into the soil and redirects it before it reaches your foundation.
How They Work
- Groundwater saturates the soil around your home
- Water enters the gravel-filled trench through pores in the soil
- Water trickles through gravel and into the perforated pipe
- Gravity carries water along the sloped pipe to a discharge point
When You Need French Drains
- Spongy, soggy lawn that never seems to dry
- Water seeping through basement walls or floor
- Efflorescence (white mineral deposits) on foundation walls
- High water table during irrigation season
- Hydrostatic pressure pushing against foundation
Why Boise Often Needs Both
The Treasure Valley's unique conditions often require a combination approach:
Boise's Drainage Challenges
- Heavy Clay Soil: Doesn't percolate well. Surface water sits; groundwater pushes laterally.
- Flood Irrigation: Raises the water table for 6 months, saturating soil.
- Flat Lots: Many subdivisions have minimal natural slope.
- Short, Intense Storms: Summer thunderstorms dump water faster than it can absorb.
Typical Solution: Surface drains at downspouts and patio low spots + French drain along the foundation to intercept groundwater.
Cost Comparison
Surface Drain (Catch Basin)
$400-$800 per basin installed
Plus $15-25/linear foot for discharge pipe
French Drain
$40-$80 per linear foot
Typical 50-foot run: $2,000-$4,000
Combined System
$3,000-$8,000
French drain + 2-3 catch basins + shared discharge
Quick Decision Guide
🌧️ Water During/After Rain Only → Surface Drain
If the problem only happens during precipitation and clears within hours, you need faster surface removal.
💧 Wet All the Time → French Drain
If your lawn is spongy even in dry weather, or your basement seeps year-round, you have a groundwater problem.
🏠 Both Problems → Combined System
Most Boise homes with significant drainage issues benefit from both approaches working together.
Not Sure Which You Need?
We offer free inspections. We'll identify your water sources and recommend the most cost-effective solution—often it's simpler (and cheaper) than you expect.