Gullies are used to collect surface water in carriageways and highway structures. The water collected is transferred to stormwater drains, manholes, box culverts, etc. Gullies are subdivided into trapped and untrapped gullies. Trapped gullies are only necessary if the connected stormwater drain is likely to be contaminated by sewage. Concrete gullies can be constructed with or without gully formers. A gully former, made of precast concrete, vitrified clay, uPVC or plastic material forms the internal basket of the gully, which is protected by in-situ concrete surround. The internal sizes of a gully formers were 450 mm in diameter and 900 mm in depth. Details of gullies can be found in Highways Department Standard Drawings.