A linear drain consisting of a trench filled with a permeable material, often with a perforated pipe in the base of the trench to assist drainage, to store and conduct water, but may also be designed to permit infiltration.  Filter drains are often used at the side of roads to collect highway run-off and at the toe of embankments to intercept run-off and groundwater flow.  The sides of the trench can be lined with permeable or impermeable lining membranes depending on specific requirements.  The filtration action helps remove suspended solids from the water.

See also French Drains.