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| Glossary » D |
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GlossaryThis glossary is copied from the Stormwater Manual of Western Australia Chapter 11: Further Information. References are available from this chapter. A B C D E F G H I J K L M N O P Q R S T U V W X Y Z DDenitrification: The reduction of nitrate or nitrite to nitrogen gas, in the absence of oxygen (ARMCANZ & ANZECC 2000). Detention/detain: The process of reducing the rate of off-site stormwater discharge by temporarily holding rainfall runoff (up to the design ARI event) and then releasing it slowly, to reduce the impact on downstream water bodies and to attenuate urban runoff peaks for flood protection of downstream areas. Detention (ephemeral/dry) basins: Areas, usually landscaped, formed by simple dam walls, by excavation below ground level or by utilisation or enhancement of natural swales or depressions, designed to temporarily detain stormwater to attenuate peak flows downstream to acceptable levels. Detention time: The theoretical time required to displace the contents of a stormwater treatment facility at a given rate of discharge (volume divided by rate of discharge). Directly connected impervious surface: An impervious surface connected directly to a receiving water body via a hydraulically efficient conveyance device (e.g. pipes or constructed drains/channels). Discharge: The rate at which a volume of water passes through a cross section in a unit of time (Water and Rivers Commission 2000b). Dissolved fraction: The part of a water sample passing through a 0.45 µm pore size filter paper. It will include both a truly dissolved and colloidal material fraction. (ARMCANZ & ANZECC 2000.) Drainage network: The system of channels and pipes and overland flow pathways which drain a catchment area (ARMCANZ & ANZECC 2000). Drainage water: Consists of stormwater runoff and/or shallow groundwater that has been intercepted by drains. |
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