Do I need a French drain or a surface drain to fix the wet spot in my yard?

Surface water and subsurface water are different problems

Surface water is what you see during and right after a storm: puddles in a low spot, a stream across the patio, a downspout emptying against the foundation. It moves fast and in volume, and it needs a surface path: grading that slopes it away, a swale, a channel drain across a walkway, or area drains with grates connected to solid pipe.

Subsurface water is what keeps a lawn spongy for days, seeps out of a slope, or saturates the soil behind a retaining wall. It moves slowly through the ground, and a grate on the surface does nothing for it. A French drain intercepts it below grade. Using the wrong type is the most common reason a drainage project disappoints.

What a French drain actually is

A French drain is a trench, typically a foot or more deep, lined with filter fabric, with a perforated pipe at the bottom and clean gravel filled around and over it. Water in the soil moves into the gravel, drops into the pipe and flows along a consistent slope to an outlet. The fabric keeps soil fines from clogging the gravel. The top can be finished with gravel as a visible strip, or capped with soil and planting so it disappears.

What makes or breaks it is the slope and the outlet. The pipe needs a steady fall toward the discharge, and the discharge has to be lower than everything the drain serves. A French drain that ends in the dirt or runs flat is a gravel trench that fills up and stops working.

Surface solutions: grading, swales and area drains

Often the simplest fix is dirt. Regrading a few inches so water runs away from the house and toward a planted low spot solves a lot of puddling with nothing to maintain. A shallow swale, a gentle planted channel, moves water across a yard in a way that reads as landscape rather than plumbing. Where water must cross a hard surface, a channel drain set flush in the pavers or a series of area drains carries it to solid pipe underground.

Downspouts deserve special attention. A single roof drain discharging onto a patio or against a wall can be the whole problem. Extending it into a solid pipe that joins the rest of the drainage is often the first thing we do.

Where does the water go?

Discharging onto a neighbor's property is a dispute in waiting, and sending silt into the street is a concern in the coastal zone. Planning the outlet is the design.

• Daylight: the pipe exits on a lower slope or at the curb, with a screened end. Simplest when the lot has fall.
• Storm drain connection: where the city allows it and the elevations work; check with Carlsbad before tying in.
• Dry well: a gravel-filled pit that lets water soak in. Works only where the soil percolates, which clay does not.
• Rain garden or planted basin: a shallow depression planted with species that tolerate wet feet for a day, useful on flatter lots.

How we approach a soggy yard

Levi walks the yard during or right after a rain when he can, because water tells the truth. He traces where it comes from, including the neighbor's slope and every downspout, checks how long the wet spot stays wet, and probes the soil. The plan is usually a combination: grade and downspouts first, a French drain where the ground itself is wet, and a clear outlet for everything. Drainage is also built into every retaining wall and paver project we do, because a wall or patio without it is a drainage problem waiting to appear.

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