Great Falls

Situated just 15 miles upstream from downtown Washington DC, the Great Falls of the Potomac River are widely considered to be one of the major waterfalls in the United States. The river splits around several jagged, rocky islands and crashes through narrow sluices in several plunges and cascades, depending on which channel is followed.
The falls are usually cited as dropping about 76 feet in all, but topographic data suggests this is all but a physical impossibility. The main channel of the river has a total drop of about 47 feet, while the smaller channels on the east side of Olmstead Island have a slightly higher total drop, but in a longer and less steep length of river than the main channel. It is unclear where the figure of 76 feet originated, but it likely is at least partially influenced by the presence of the dam just upstream of the falls which diverts a portion of the river into the Chesapeake and Ohio Canal. Even taking the height of the dam into account, a cumulative drop of 76 feet can only be accounted for by traveling 1.8 miles downstream from the dam (or if excluding the dam, over 2 miles downstream from the top of the falls).
As mentioned previously, the dam above the falls diverts a portion of the river away from the falls, such that the falls only resemble their naturally occurring form for about six months out of the year. It isn't known exactly how much water is diverted away from the falls, but based on pictures it appears it may be anywhere from one-quarter to half of the volume of the river, depending on the season. As such, the figures we have listed for the volume of the river may not necessarily be an accurate representation of the amount of water which actually runs over the falls (the figures were taken from a USGS stream gauge located several miles downstream).