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).
Glossary Group: G
Greenfield Runoff
This is the surface water runoff regime from a site before development, or the existing site conditions for brownfield redevelopment sites.
Gully
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.
Groundwater
Water that is below the surface of the ground within the saturation zone.
Gross Solids
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.
Greywater
Wastewater from sinks, baths, showers and domestic appliances.
Greenfield / Greenfield Site
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.
Gravity System
A drain or sewerage system whereby flow is caused by the action of gravity and where the pipeline is designed to operate partially full.
Gradient
The angle of inclination (of pipe), which dictates its capacity and velocity of flow.