It is the shape of the land, combined with one of the events described above, that create perfect conditions for a flood. The Potomac River narrows dramatically just below the Falls, as it enters Mather Gorge. This creates a narrow chokepoint, through which all of the water must flow on its way downstream. As water begins to flow into the Potomac from the streams and smaller rivers that empty into it, the water turns brown from the eroded sediment and dirt. The water starts backing up at the mouth of the gorge, and fills the basin behind it. Eventually, the falls will disappear underwater. It takes a few days after the worst of the rain ends, or snow melt is over, before the river crests at Great Falls Park.
Potomac Potomac River
Potomac Potomac River