A runnel, also known as a French drain, is a linear ditch filled with gravel, stone, rock or pavers that redirects surface and groundwater away from an area where runoff has become problematic. The pervious makeup of a runnel also allows for some infiltration of stormwater runoff back into the water table. Runoff that is not infiltrated is directed to a location, like a rain garden or bioswale, where it can be properly dealt with. An effective runnel is trapezoidal in shape and slopes enough to move water through the drainage system. Elements used in creating a runnel include a dug ditch, aggregate, geo textile landscape fabric, a perforated tile or drainage pipe and a top layer of stone or paver-like material.