The
water that accumulates in large amounts in
urban areas because of
impervious surfaces like
pavement,
rooftops, and
roads (
Forests,
grasslands, and
wetlands allow
precipitation to filter into the
ground). Usually channeled away through
storm drains and
storm sewer systems into
local streams.
Runoff in urban streams contributes to streambed erosion, fluctuations in water level, higher water temperatures, increases in sediment loads. Both urban streams and downstream water sources see increases in pollutants (grease, oil, litter, garden pesticides, road salts, and heavy metals) from urban runoff.