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Waterfalls: What Defines Them?

We’ve had a lot of requests for Jim Parham’s Waterfall Hikes of North Georgia this week. All the rain this spring has made for spectacular waterfalls in the region. That got us thinking: What defines a waterfall? To answer that question, here’s an adapted excerpt from the aforementioned guidebook. The first version was written by Thomas E. King and originally appeared in his Waterfall Hikes of South Carolina. We think this passage goes a long way to explaining what qualifies as a waterfall and describing the many different types. Note: the examples of each type listed here are to be found in Waterfall Hikes of North Georgia.

What Is A Waterfall?
A precise definition of a waterfall is difficult to find. Most dictionaries and encyclopedias refer to a waterfall as a more or less vertical stream of water that flows over the edge of a cliff that has eroded away. A waterfall is also sometimes defined as a cascade of water crossing rocks that have not yet eroded, producing what is commonly known as a rapid, although a cascade is a generic term for any flow of water. A small creek can be said to cascade downstream over rocks. A cascading flow of water can be any height, from a few inches to several hundred feet. Each section of a waterfall is sometimes referred to as a cascade.

Different sources set different minimum heights, ranging from 5 to 20 feet, for descending water to qualify as a waterfall. Other points to consider:

  • Must water flow over the falls be constant?
  • What is the minimum volume of water flow acceptable (e.g. cubic feet per second) to qualify as a waterfall?
  • What is the minimum degree or angle at which the water must fall or flow downstream?
  • What is the origin of the waterfall—a  constantly flowing stream, a spring from beneath the earth, melting ice or snow?

The following criteria are used to define a waterfall:

  • A waterfall is a complete unit, sometimes composed of two, three, or more segments. Two segments miles apart are considered two separate waterfalls.
  • Segments (each with a significant drop) only 10 feet apart can qualify as a section  (e.g., upper, middle, or lower) of the same waterfall. To qualify as a waterfall, one segment of the falls must be at least five feet high.
  • Most generally accepted true waterfalls must be located on a river, creek, or stream that provides a source of water at least annually.
  • Most waterfalls have a significant amount of water flowing over boulders or plunging down a cliff. However, some very low-volume waterfalls are attractive because of the shape of the rocks or the striations of color in the rocks over which the water flows. Such low-volume flows are called trickles.
  • One day a waterfall can be a gentle trickle of water gracefully gliding over bedrock. The very next day after a rainstorm, that same waterfall changes its nature and shouts out its presence with a thunderous rush of water.
  • Some people might say that the shoals, rapids, and low-flow trickles listed in this book are not waterfalls. However, based on observations and information in other guidebooks, every waterfall listed meets the requirement of water dropping five feet or more in elevation over a very short distance.

Waterfall Structure & Classification
Waterfalls are classified into the following categories according to the physical structure of the segments:

  • Block
    A wide flow of water extending uninterrupted across a river or creek.
  • Cataract
    Typically occurring on torrents (large rivers), with a high volume of water.
  • Fan
    A falls that widens at its base.
  • Horsetail
    Water falling in a vertical drop, then making contact with the rock surface behind the water, causing the water to spray out or change direction from the original path.
  • Plunge
    A fall of water that makes no contact with the rock surface behind it; also called a freefall.
  • Rapids
    A turbulent flow of water, usually through rocks, often navigated by whitewater rafters and canoeists. Rapids are ranked as Classes I through VI, in ascending order of difficulty. Rapids usually consist of less than a single five-foot drop.
  • Segmented
    Parallel falls where several streams (or part of one stream) flow over the same ledge side by side (twin, triplet, etc).
    (Example: Upper Falls on Blood Mountain Creek, p. 182)
  • Sluice (Chute)
    Water descending through a constricted passage.
    (Example: Upper Falls on Holcomb Creek, p. 216)
  • Tiered
    Water flowing in multiple drops over several sections of the falls (double, triple, quadruple).
    (Example: Desoto Falls, p. 186)
  • Waterslide
    Water gliding in a thin sheet over slick or mossy rock slabs.
    (Example: Bridal Veil Falls, p. 265)

Many waterfalls are combinations of the segments listed above. For example, Upper Falls on Low Gap Creek (p. 162) starts with a slide, then ends in a plunge.

Rating Waterfalls
A useful rating system for waterfalls is as follows:

  • Nice
    These waterfalls are usually small (5-15 feet high) with a low volume or trickle of water. May appeal only to serious waterfall buffs.
  • Fair
    Small waterfalls (10-30 feet) on smaller streams.
  • Good
    Larger and higher falls (25-75 feet). Usually very photogenic.
  • Excellent
    Very appealing (50-100 feet). Considered beautiful, very photogenic.
  • Spectacular
    Impressive in size (100 feet and higher) and water flow. Ideal for viewing and photographing.

It’s important to note that the pleasure afforded by a waterfall does not correspond to its rating. Rating a waterfall is very subjective. Even falls rated only fair may be very appealing, depending on the perception of the observer.

Measuring Waterfalls
Many criteria used for classifying waterfalls are subjective. For example, the height of a falls is measured from the uppermost precipice over which the water flows to the lowest point of contact in a pool or stream or over boulders. However, what constitutes the base of a falls is often a matter of opinion. Most reported heights of waterfalls are only estimates. Even if the height were measured with sophisticated devices, the actual top and bottom of the falls would have to be identified before measuring, and sometimes that is not possible.

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