Editing Drainage (section)

===Geotextiles===
New storm water drainage systems incorporate [[geotextile]] filters that retain and prevent fine [[Particle size|grains]] of [[soil]] from passing into and clogging the drain. Geotextiles are synthetic textile fabrics specially manufactured for [[civil engineering|civil]] and [[environmental engineering]] applications. Geotextiles are designed to retain fine soil particles while allowing water to pass through. In a typical drainage system, they would be laid along a trench which would then be filled with coarse [[granular material]]: [[gravel]], [[sea shells]], stone or [[rock (geology)|rock]]. The geotextile is then folded over the top of the stone and the trench is then covered by soil. [[Groundwater]] seeps through the geotextile and flows through the stone to an outfell. In high groundwater conditions a perforated plastic ([[Polyvinyl chloride|PVC]] or [[Polyethylene|PE]]) pipe is laid along the base of the drain to increase the volume of water transported in the drain.

Alternatively, a prefabricated plastic drainage system made of [[High-density polyethylene|HDPE]], often incorporating geotextile, [[Coir|coco fiber]] or [[Cloth|rag]] [[filter (water)|filter]]s can be considered. The use of these materials has become increasingly more common due to their ease of use, since they eliminate the need for transporting and laying stone drainage aggregate, which is invariably more expensive than a synthetic drain and concrete liners.

Over the past 30 years, geotextile, PVC filters, and HDPE filters have become the most commonly used soil filter media. They are cheap to produce and easy to lay, with factory controlled properties that ensure long term filtration performance even in fine silty soil conditions.