FRENCH DRAIN: The ubiquitous French Drain, what is it; hidden, invisible, unobtrusive, just out of site and out of reach, subtle and misunderstood, it stands guard against aggressive aqua slowly sacrificing itself if required to protect. It's a ditch filled with stone, and buried; an underground lay of pipe full of loose joints or holes, opening to daylight at an un-obvious termination. It's inside and outside, at the base of a wall or the foot of a hill but always underneath. Put in once and forgotten until through service it becomes rotten, and water once again flows where we wish our feet to trod and no water be allowed to expose. It's perceived demise brings panic to some of our best and then to renew its repose they heavily invest.

The "French" drain type construction technique was used by the Romans and others., so it may originally have been "Trench" drain. For now, it's just nomenclature. The term may be limited to the building trades or may just be colloquial to certain areas.

"French Drain" means a buried drain system used to collect and channel water in a controlled manner. Not unlike a storm sewer or underground pipe, but different in that the pipe may be perforated or have loose joints, may collect water along its entire length and usually is utilized for subtle, slow moving, or small-but-steady amounts of water such that a ground surface drying affect is produced in a given area.

An exterior French Drain used to remove surface water, is constructed by digging a trench or ditch a given depth and length, filling the trench up with a fairly solid but permeable material such as river gravel or crushed stone; usually with a perforated pipe laid at the bottom of the trench and traveling its entire length. The bottom of the trench should be below the frost line, but sometimes at or below the lowest point of a structure it is intended to protect (to intercept the water and direct the it away from the structure). The bottom of an exterior French Drain ditch must be sloped downward if it is not cut into a hill or natural slope. When used to collect surface water, such as at the base of a hill, it is often left open at the top (so the gravel can be seen at the surface); when intercepting significant amounts of surface run-off, if the gravel or stone does not travel all the way to the top of the surface ( to "daylight"), it may not work well, or at all.

Sometimes French drains are used to remove water from the base of a hill, when the hill terminates into a yard or level area desirable for use. Or, to place the water of a weeping or spring filled hillside below the surface to keep the surface dryer, and therefore manageable.

French Drains are commonly used behind retaining walls.This is most effective on large or tall walls of poured concrete, or brick/stone laid up with mortar (because there is no easy way for water to escape from the wall). "Dry Walls" are laid up of stone or interlocking concrete block with no mortar. "Dry Walls" may allow trapped water to escape almost anywhere in the wall where water builds up, and are less in need of rear (internal) drainage. Proper use of a French Drain behind a retaining wall (gravel and pipe at bottom rear of wall, with pipe traveling parallel to the base of the wall, connecting eventually to a lower relief point), when used on a solid type wall, this does preserve the wall, and may extend its life indefinitley.This is most effective when the pipe has a large diameter of six (6) to eight (8) inches or more, and the high side of the wall has some type of ground surface treatment to minimize the lingering of water immediately behind the wall.