Stormwater Source Control Design Guidelines 2005 - Waterbucket

Glossary Stormwater Source Control Design Guidelines 2005Subsurface Infiltration Structure – any type of undergroundstructure designed to receive water from the surface byinfiltration (e.g., through porous paving) or conveyance (e.g.,via a swale with drain outlet) and temporarily retain it to allowgradual exfiltration of the water into the underlying structuralor native subsoil. They may be individual, isolated structures(e.g., rock pit, soakaway, dry well, sump, plastic voidstructures, perforated or “leaky” tank or catch basin, drainrock blanket) or linear (french drains, underdrains, plastic voidchambers, underground infiltration trenches). They arefrequently combined with surface structures such as swales,rain gardens or porous paving.Swale – a linear depression or wide, shallow channel used tocollect, infiltrate, treat and convey stormwater. A variety oftypes of swales and related terms are identified in theliterature:• Grassed swale – lined with grass, named presumably todifferentiate from a rock or concrete lined swale;considered as typically dry between storms. The grass actsto decrease stormwater flow velocities; reduce peak flowrates, reduce flooding and erosion, and promoteinfiltration, thereby reducing the overall runoff volume.Removal of contaminants can be accomplished throughfiltration of suspended solids by plant stems, adsorption tosoil particles and plants, infiltration, and some biologicalaction. (GVRD, 1999: 4-52).• Vegetated swale – a variant on the grassed swale that ismore densely vegetated or landscaped with plants otherthan grass. The same attenuating, infiltration andcontaminant removal characteristics apply.• Wet swale – grassed or vegetation swale with standingwater between storms, due to high groundwater levels orhigh base flow; alternatively, may be purposely designedwith check dams that store water in shallow pondingareas. Check dams help to reduce flow velocity, promoteinfiltration and evapotranspiration, enhance settling ofparticulates and contaminant removal. Wet swales areplanted with water tolerant or wetland plant species, withturf on the side slopes.• Bioswale – a term to collectively refer to grassed,vegetated or wet swales.• Dry Swale with Underdrain, Bioretention swale, Infiltrationswale – a shallow grassed channel designed to enhanceinfiltration by containing check dams or weirs to createshallow ponds of stormwater and promote infiltrationthrough an augmented soil bed to an underground drainrock reservoir and ultimately into underlying soils. A130Greater Vancouver Sewerage & Drainage District