This test is necessary for drainage applications. The permeameters can be of parallel flow or radial flow type. In either case, flow occurs along the plane of the permeameters. In the apparatus, flow occurs radially outwards, from a central hole to the periphery of a circular specimen. The inplane permeability is known as transmissivity which is defined as the volumetric rate of flow per unit width of geotextile and unit hydraulic head. Specimen diameter is 100 mm.