Karez

(Persian; literally, an underground irrigation channel), an underground structure for collecting groundwater and conveying it to the surface. Such structures are in use in the mountainous and foothill areas of Middle Asia and Transcaucasia. Water from a karez is used for water supply and irrigation.

A karez consists of one or more water-catchment tunnels 1.0–1.4 m high and 0.5–0.6 m wide, with reinforced walls laid through a water-bearing horizon, as well as vertical ventilation wells and a water tunnel connected to a discharge channel. Karez tunnels can be as much as several kilometers long. The average yield of a water-catchment tunnel is 0.3–0.6 liters per sec per meter of the tunnel.