Montgomery County, Maryland, United States
Regulated FlowThis waterfall has been regulated by Hydroelectric development and may no longer flow consistently. The waterfall may have reduced flow, seasonal flow, or may no longer flow at all due to the diversion of its watercourse.
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).
History and Naming
Great Falls is the Official name of this waterfall.
Has also been known as:
- Great Falls of the Potomac
Location & Directions
Coordinates: Unknown Elevation: 129 feet USGS Map: Seneca 7 1/2"
By The Numbers
The information presented in this table is meant to help identify and clarify the physical aspects of the waterfall for comparative purposes. While we try to ensure this information is as accurate as possible, sometimes it will prove necessary to either estimate or flat out guess at certain characteristics where either enough information isn't readily available, is not known, or we were not able to confirm a given trait upon surveying. This information may be changed at any given time to ensure accuracy.
The Total Height listed for the waterfall represents the difference in elevation from the top of the uppermost drop, to the bottom of the lowermost drop of the waterfall, including all stretches of interstitial stream in between. Stream between two tiers of a waterfall is counted in its overall height regardless of whether or not that section of the stream would be legitimately considered a waterfall on its own right, were it to be isolated. Waterfalls with only one drop will of have the height of only the single drop listed here.
The Tallest Drop figure represents the height of the largest single drop within a multi-stepped waterfall. Waterfalls with only one drop will have the total height of the waterfall repeated here.
Num of Drops
The Number of Drops in a waterfall is a tally of the total number of distinct drops which make up the waterfall. Stretches of interstitial stream in between two or more distinct drops of a single waterfall are NOT considered to be distinct drops of the waterfall unless the section of stream in question would otherwise qualify as a waterfall were it to be isolated.
The Average Width of the waterfall represents the breadth of the waterfall from bank to bank under typical flow conditions, or if the waterfall has been Cataloged, under the conditions which it was most thoroughly surveyed. Often this number will be approximated because of a lack of approachability to many waterfalls. We often utilize Google Earth to measure the width (where imagery is of sufficient quality and resolution to allow it.
Maximum Width represents a hypothetical measurement of roughly how wide a waterfall could get during peak streamflow or flood conditions. For smaller waterfalls, this figure will generally not differ much from the Average Width measurement, but for broader waterfalls - especially those that feature a crest that isn't constricted - this figure can at times be consideraby larger. Like the Average Width measurement, this measurement will take into account the difference in width at the top and bottom of the waterfall as much as possible, but will often be made based on the width of the crest of th falls alone.
The Pitch of a waterfall is an estimated - often very roughly - measure of the average slope or steepness of a waterfall. The Pitch figure only takes into account sections of stream which are actively falling. Pools or stretches of level stream in between two or more successive drops of the falls will not factor in this figure. As an example, a waterfall which features two truly free-falling leaps separated by several dozen yards of flat stream will have a Pitch of 90 degrees. Similarly, a waterfall with two drops separated by a pool, one with a true free-falling drop, and one with a Horsetail type fall will average the two, so while the Plunging drop has a Pitch of 90 degrees, if the Horsetail drop has a Pitch of 45 degrees, the total Pitch will be roughly 67 degrees.
The Run of a waterfall is a measurement representing the total linear distance on the ground between the top and bottom of a waterfall. This figure is not often easy to establish with a high degree of precision and as such will often be estimated. Waterfalls with a longer Run will usually either be less steep, often cascading type waterfalls, or will feature multiple steps separated by shorter stretches of a more gradual gradient streambed.
The system of classification of waterfall forms we use is a heavily modified derivative of the classifications outlined by Greg Plumb in his "Waterfall Lover's Guide to the Pacific Northwest" books. While plumb uses eight distnct forms, we wanted further granularity and opted to break down the hierarchy twofold: first based on the overall pitch of the waterfall, and then based on what shape the fall takes as it makes its descent. There are five primary Categories of falls in this system: Plunge, Horsetail, Steep Cascades, Shallow Cascades, and Rapids. Additional deliniation is then applied depending on characteristics such as the breadth of the falls, whether it splits into two or more channels, whether it falls in multiple successive drops, etc. For more information on our waterfall form classifications, see the Help page.
The watershed which a waterfall occurs within, if it is specified, will be based on the ultimate distributary watercourse to the ocean. For example, Washington's Palouse Falls occurs along the Palouse River - which is a tributary to the Snake River, which is itself a tributary to the Columbia River, which ultimately enters the Pacific Ocean, so Palouse Falls would then fall within the Columbia River watershed. Streams which empty directly into the ocean, or into a minor basin which then empties to the ocean will often have this field left blank.
The name of the watercourse which the waterfall occurs along. If the watercourse is not known to have an officially or colloquially recognized name, this field is left blank.
The volume of water present in the stream at the location of the waterfall. This is often the most difficult figure to pin down because accurately measuring streamflow is not a simple process. We will rely on USGS data as much as possible, and attempt to take into account seasonal fluctuations in stream levels if possible. There is no guarantee that this figure will be accurate, and in cases where there is no USGS data to use, it may be a very, very rough estimate at best.
If known, the primary source of the watercourse which produces the waterfall will be listed here. This is helpful in determining whether a waterfall may flow more consistently during certain periods of the year - streams which originate in Springs, Lakes, or Glaciers will often flow more consistently throughout the year than those fueled by simply Runoff. The source of the stream may also be either unknown or undetermined.
A rough estimation of how many months out of the year the stream which produces the waterfall will actually hold water. The vast majority of waterfalls featured on this website will technically be truly perennial waterfalls (those that flow all year long), but some may see their flow dwindle greatly in the late summer months. This figure will not take into account the winter months when the waterfall may freeze, because in such cases the waterfall will very often be inaccessible. Entries which specify a Flow Consistncy of 12 Months should in general have an acceptable flow at any time of year (but may be better during certain periods - see below).
A general estimate of the best period of the year during which time the falls will be considered at optimal conditions, or flowing at their best. There may be variance within the range specified where the flow will be better or worse, but visiting at any time in the range specified (if available) will generally present the waterfall in its best light.Close
CatalogedWaterfalls which are Cataloged we have visited and surveyed in person. Statistical information should be quite accurate (for the most part), and exact measurements will often be available (information is not guaranteed to always be up to date). Detailed information, directions, and photographs will almost always be available.
ConfirmedConfirmed Waterfalls are known to exist, should be relatively accurately mapped and geotagged, and the statistical information available will often be dependable. If height information is presented, it may be estimated but should be accurate. Directions will not likely be available.
UnconfirmedUnconfirmed Waterfalls are often marked on a published map, but we have yet to confirm the exact location and / or whether or not its stature is significant enough to qualify for listing in the database. Statistical information may be estimated and may be inaccurate. No directions.
UnknownWaterfalls marked as Unknown are either suspected to exist based on heresay or a hunch, or we have received unverified information suggesting a waterfall may exist near the location provided but cannot corroborate it in any way. Geodata may not be accurate, the location may not be known at all, and statistical information will be estimated and highly inaccurate.
InundatedInundated Waterfalls have been submerged beneath lakes or reservoirs, usually a result of impoundment of a river behind a dam, and most often no longer functionally exist (there may be rare exceptions). We maintain records for these features out of historical importance.
SubterraneanThough not common, some waterfalls can be found entirely underground within cave systems. Access to subterranean waterfalls can vary from easy via developed walkways to requiring a high level of extremely technical spelunking skill, including familiarity with ropework and a distinct lack of claustrophobia.
DisqualifiedWaterfalls which have been marked as Disqualified do not have the necessary stature or features to qualify as a legitimate waterfall according to our criteria. We will maintain records for entries with this status where the feature is well known and / or may have been historically referred to as a waterfall at some point in time.
PostedPosted Waterfalls are known to exist, and we may have a large amount of information associated with them, but are located on private property and are not legally accessible to the general public. Accessing waterfalls with this status should not be attempted without first being explicitly granted permission of the property owner.