A roof with plants growing on its surface, which contributes to local biodiversity. The vegetated surface provides a degree of retention, attenuation and treatment of rainwater, and promotes evapotranspiration. (Sometimes referred to as an alternative roof).

This is the surface water runoff regime from a site before development, or the existing site conditions for brownfield redevelopment sites.

A structure to permit the entry of surface water runoff into a sewerage system. It is usually fitted with a grating and a grit trap.

Water that is below the surface of the ground within the saturation zone.

Solids, usually organic in nature, either floating, suspended or deposited, which have a polluting effect on a receiving water. Often restricted to visible solids with one dimension in excess of 25mm.

Wastewater from sinks, baths, showers and domestic appliances.

New development, usually at the periphery of existing urban areas. This creates increased rainfall-runoff and has an impact on existing sewer systems and watercourses.

A drain or sewerage system whereby flow is caused by the action of gravity and where the pipeline is designed to operate partially full.

The angle of inclination (of pipe), which dictates its capacity and velocity of flow.