A Glossary of Commonly Used Grand Canyon Rafting Terms
Below is a list of the commonly used Grand Canyon rafting terms you’re likely to hear on a rafting adventure with us. You’ll hear your guides chatting about the breaking waves, debris flow, the water volume, the lip and many more of these.
Big Water: Large Volume, fast current and big waves, often accompanied by huge reversals and extreme general turbulence.
Breaking waves: Where the top of the wave has collapsed over itself, creating a white, frothy look.
Confluence: The point where two or more rivers meet.
Cubic Feet per Second (CFS): Defines the volume of water one foot deep and one foot wide flowing a distance of one foot in one second. One cfs is equal to 7.48 gallons of water flowing each second.
Debris Flow: Fast moving, liquefied landslides of mixed and unconsolidated water that look like flowing concrete.
Flash flood: When a large amount of water (usually caused by rain) flows through an area. This typically occurs in the side streams, tributaries and slot canyons in the Grand Canyon.
Gradient: The “steepness” of a river, measured in feet of elevation loss per mile of river. Average gradient is the average over the total length of a section of river.
High Volume: A large amount of water passing through an area of the river.
High Water: River flow above an expected average. It makes the currents faster and some rapids easier. Other rapids become more difficult.
Hole(s): Where water flowing over a rock or other obstacle flows down, then back onto itself in an frothy foam of whitewater.
Horizon Line: Usually indicative of a fall or steep drop. There is a line to run, but the route, if there is one, is not apparent. This means the guides will get off the rafts and start scouting the rapid if they are not familiar with it.
Hydraulic(s): Also defined as waves or holes. On a river, they’re created by water running over different obstacles and drops in gradient on the river bed.
Hydraulic Jump Wave: The rise of water level, which takes place due to the transformation of unstable shooting flow (super-critical) to the stable streaming flow (sub-critical flow). It frequently occurs in a canal below a regulating sluice, at the toe of a spillway, downstream of a narrow channel or at the place where a steep channel slope suddenly turns flat. On the Colorado River in Grand Canyon, it occurs downstream of a narrow channel, or at the place where a steep channel slope suddenly turns flat.
Keeper: A hydraulic reversal capable of trapping a raft or sometimes people for long periods (see holes above).
Lip: The name of the entrance to the rapid. The instant you go over the edge of the horizon line (see definition above), and head down into the rapid, you are going over the lip.
Standing wave: Interchangeable with tail waves (see definition below).
Tail waves: Generally, the smaller waves at the end of a rapid.
Technical rapid: Requiring moves around rocks or hydraulics to successfully navigate a rapid. The more moves, the more technical a rapid.
Tongue: The smooth “V” of fast water found at the head of rapids.
Volume (high or low/big or small): Terms used for describing the amount of water flowing through a given channel.
Wave Train: A series of standing waves in close succession.
