Ag drain
An ag drain is a perforated pipe in a gravel trench used to collect and redirect subsurface water. Common behind retaining walls and along footings.
Ask Chalkline about this →An ag drain (agricultural drain) is a perforated flexible pipe laid in a gravel-lined trench to collect and redirect subsurface water away from structures. On a residential job, ag drains are used behind retaining walls (to relieve hydrostatic pressure), alongside footings and slabs, and in low-lying garden areas prone to waterlogging.
The gravel surround allows groundwater to enter the perforated pipe and flow to a legal discharge point (surface pit, kerb, or stormwater main). Without adequate drainage relief behind a retaining wall, hydrostatic pressure builds and can cause wall failure. Ag drain installation is typically landscaper or earthworks scope; discharge connection to the council stormwater system requires a licensed drainer.
Also known as: agricultural drain, ag pipe, French drain, subsurface drain.
Category: Drainage / earthworks.
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Last updated: 2026-05-10. Verified: 2026-05-10.