Slide 79 of 110
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Often, code requirements discourage the storage and treatment of rooftop runoff on individual lots, thus bypassing opportunities to promote bioretention and infiltration. Most subdivision codes require that yards have a minimum slope to facilitate drainage away from house foundations for fear of nuisance ponding, basement flooding, or ice formation on driveways or sidewalks.
Sending rooftop runoff over a pervious surface before it reaches an impervious one can decrease the annual runoff volume from residential development sites by as much as 50%. Some possible techniques to encourage treatment of rooftop runoff on-site include directing flow into stormwater treatment practices (infiltration swales, infiltration trenches, or dry wells), encouraging sheet flow through vegetated areas, directing runoff to depression storage areas, or using a rain barrel.