Bull Run and its tributaries threated sewer infrastructure in Prince William County
Streams move their channels naturally within their floodplain. The energy of moving water erodes streambanks, changing the location where the stream curves. At times, a shift in the channel may isolate old paths and create "oxbows," named for their resemblance to the wooden frame used to harness oxen to pull wagons in the colonial era.
Patterns of riffles and pools move, as streams lower their base level are erode their bottoms. On the sides of streams, trees are naturally at risk of being undercut as channels migrate.
Bull Run etches away at the streambanks between Prince William and Fairfax counties, shifting naturally within its floodplain
Agriculture and modern development have altered the speed and quantity of rainwater runing off the ground into streams. Faster runoff from impervious sufaces, especially rooftops and pavement in urban/suburban areas, results in unnatural flooding. Stream channels which had evolved based on a surrounding forest overflow after receiving more water in a shorter period of time. The extra water, with its extra speed, etches the sediments in a floodplain and causes streams to threaten nearby structures.
raindrops that land on parking lots race quickly to streams rather than soak into the soil
Stream restoration projects are deigned to reshape the channel to hadle extra flow, and to capture some of the runoff in stormwater ponds that slow the release of rainfall.