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[[File:David Elkin downspout disconnection to constructed stream channel.jpg|thumb|Downspout routed to an [[infiltration trench]]
, [[trench drains| trench drain]] visible in the background.]]
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.