Downspout disconnection

Downspout disconnection programs are common in many older urban centers. They require that residents retroactively disconnect their downspouts from the municipal sewer system. This is due to older sewer systems being undersized for the combined flow of sanitary waste and stormwater.

New projects should consider remaining independent of municipal storm sewers from the outset. To prevent flooding and achieve stormwater control, widespread use of small, site scale technologies such as downspout disconnection can reduce the size of shared LID installations.

The Ontario Building Code requires that:
"Where downspouts are provided and are not connected to a sewer, extensions shall be provided to carry rainwater away from the building in a manner that will prevent soil erosion."[1]

Recommended strategies to receive downspout runoff include:

• Rain Barrels
• Rain Gardens
• Infiltration Trench

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Irrigation technology	Benefits	Disadvantages
Spray	Maximizes evaporation	Requires higher water quality standard.
Drip or capillary	Harvested rainwater is readily used without further treatment Uses less water	Planting medium does not 'wick' water sideways readily, so can lead to localized dry areas

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  Downspout routed to an infiltration trench.

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Surface runoff from at-grade surfaces, resulting from rain or snowmelt events.

Low Impact Development. A stormwater management strategy that seeks to mitigate the impacts of increased urban runoff and stormwater pollution by managing it as close to its source as possible. It comprises a set of site design approaches and small scale stormwater management practices that promote the use of natural systems for infiltration and evapotranspiration, and rainwater harvesting.

(1) The wearing away of the land surface by moving water, wind, ice or other geological agents, including such processes as gravitation creep; (2) Detachment and movement of soil or rock fragments by water, wind, ice or gravity (i.e. Accelerated, geological, gully, natural, rill, sheet, splash, or impact, etc).

The portion of water precipitated onto a catchment area, which then flows as surface discharge from the catchment area past a specified point.

Water from rain, snow melt, or irrigation that flows over the land surface.

Human application of water to agricultural or recreational land for watering purposes. City of Toronto Wet Weather Flow Management November 2006 47

Abiotic transfer of water vapour to the atmosphere.