Backyard Drainage — French Drains, Channel Drains, and the Monsoon Plan
Where to put each drain type, how deep, and the AZ-specific design that handles 2 inches of rain in 20 minutes.
Match the drain to the problem
- Channel/trench drain: hardscape areas where water sheets toward the house or pool.
- French drain: low spots, against retaining walls, anywhere subsurface water pools.
- Catch basin: low point of a yard where surface water collects.
- Dry well: terminus when there's no street/alley to daylight to.
Sizing for AZ monsoon
Phoenix monsoons can dump 1–2" in 20 minutes. Design to handle 3"/hr conservatively. Channel drains: 4"+ wide for paver decks, 6"+ for sloped driveways. French drains: 4" perforated SDR-35 pipe wrapped in geotextile, in a 12"×18" gravel envelope. Catch basins: 12" minimum with 4" outlet.
Where to outlet
Best: gravity-daylight to a street/alley. Acceptable: dry well sized at 1 cu ft per 5 sf of contributing surface. Never: across property line to neighbor (HOA violation and a city code violation in most cities).
Retrofitting an existing yard
Channel drains can be saw-cut into existing pavers without ripping the whole deck. French drains can be trenched along a wall behind a planter. Re-grading near the foundation (always 6" fall in first 10 ft) often solves problems with no new pipe at all. We do drainage audits before the next monsoon — free for AE clients.
