Indian Rock Art

Environment Terminology

Kayaking terminology used to name features in rivers and oceans

River Features

Diagram of a river
Pool
Deep calm water.
Riffle
Shallow and rocky area with relatively minimal gradient with surface disturbance.
Rapid
Shallow and rocky area with relatively steep gradient, causing an increase in water velocity and turbulence.
Tailout
Shallow area at the end of a pool (type of riffle).
Run
Deeper water with a smooth, uniform current. Also refers to the path taken a paddler down a set of rapids.
Eddy

Water "bounces" off an obstruction creating a calmer area behind it that draws water back towards the obstruction from downstream. The calm or gently flowing upstream area of water is the eddy. A swirling reverse current.

Paddles can peel out into many eddies and scout out the next rapid or simply have a rest. While eddies are generally calmer areas of a river, large eddies can create powerful currents that can trap or flip boats.

Eddy Line (Fence)
Boundary between the main downstream current and calmer upstream eddy current
Eddy Wall
Eddies are often lower than the main current creating a step or "wall" along the eddy line. This can make leaving an eddy difficult in big water.
Waterfall

Where water cascades down a ledge.

Crest (Brink)
The top of the waterfall where the water starts falling.
Base (Foot)
The bottom of the waterfall when the water stops falling.
Drop (Height)
Vertical distance from the crest to the base of the waterfall.
Roundout
Horizontal distance from the crest to the base of the waterfall
Laminar
Term used for smooth water in fluid mechanics.
Turbulence
Term used for turbulent water in fluid mechanics.

There is no exact point where a riffle becomes a rapid. Most Grade I rapids would probably be called riffles by experienced paddlers that are familiar with the term. In general, riffles will have consistent and fairly small rocks or gravels with a very gentle gradient and rapids will have boulders of varying sizes with a steeper gradient.

Whitewater
Rapids have enough turbulence to trap air in the water making it appear opaque and white.
Constriction
River's flow is forced into a narrower channel. This will either cause a run or a rapid depending on the streambed topography.
Obstruction
Streambed topography, boulders, logs or man-made structures.
Pillow (pressure waves)
When water flows backwards upstream of the obstruction. The water appears to "pile up" or "boil" up against the obstruction. This usually indicates the obstruction is not undercut, but not always.
Pour over
Water flows over the obstruction.
Hydraulics (Hole)
The river flows back on itself. Term "hole" is used as the aerated water provides less buoyancy and can feel like an actual hole in the river.
Waves
A large, smooth face on the water created in a hydraulic. A series of waves or a "wave train" can sometimes be created.
Wash out
Term used when an increased flow reduces the rapids difficulty.

Note that the angle of the water around an obstruction could either create an eddy (flowing sideways) and / or a hole (pulling downwards).

Bend

Curve in the river.

Outside
Taking the longest path around the bend. Water tends to flow fastest and deepest, but there tends to have dangers like strainers / sweepers or undercut banks. Outside banks can often create waves.
Inside
Taking the shortest path around the end. Usually shallower and slower.

If unsure about a bend, keep your bow slightly angled towards the inside to allow you to paddle away from the outside quickly. There will often be an eddy line formed that will quickly pull out, albeit you often lose a lot of momentum because of these.

Chute

Water is forced between two bounders creating a downstream V.

Tongue
The smooth water in the chute.
Tail waves
Series of waves that are often found at the bottom of the chute where the two eddy lines join.

Upstream V marks a bounder or other obstruction in the water. It is best to avoid and if that can not be avoided, lean into these to avoid a potential capsize, especially where there is no visible pillow.

River Dangers

Strainers or sifts
Submerged objects that can catch a kayaker or their boat while allowing water to flow freely past, just like a food strainer or colander. These can be storm grates, fences, trees that have fallen into a river ("log jam") or even exposed tree roots.
Sweepers
A tree that is fallen or leaning into the river but not fully submerged and is still anchored to the shore.
Holes

Larger hydraulic where the surface water to flow back upstream toward the object. Dangerous as these can be trapped in the recirculating aerated water that can be difficult to exit.

Also known as "stoppers" or "souse-holes".

Frown
Water is flowing out of both ends of the hole making it easier to exit. The whitewater of the hydraulic looks like a frown from downstream
Smile
The edges of the hydraulic are pointing upstream, making it difficult to exit.
Low-head Dams (Weirs)
One of the least concerning looking hazards is actually one of the most lethal dangers that paddlers will encounter. Weirs tend to be uniform and fairly wide allowing them to create a perfect hydraulic across the structure that even the most experienced paddler may not be able to escape.
Undercut

Undercuts form when rocks have been worn down underneath the surface by the river. Undercuts can occur on the streambed or boulders within a river. Often undercut bounders will lack obvious signs of a pillow on the upstream side.

Since the current flows under the rock, undercuts can easily prove fatal as they suck a boater down under the bounder where there is the possibility of the boater being pinned underwater.

Leaning towards the boulder will make it less likely that you will get pulled under. Leaning away from the boulder allows the current to catch your upstream edge, pulling the boat under.

Runs will often create undercuts in riverbeds / gorges, especially common in softer rocks such as stonestone. These areas should be avoided.

Waterfalls commonly create undercut features behind the base.

Sieves (Slot)
Narrow space that allows water to flow freely, usually two boulders. This creates a high flow through the sieve and can force water up behind the sieve creating turbulence.
Entrapment
Usually when a foot or arm gets trapped between two boulders. This is why paddlers use a defensive swim where they float downstream with their feet raised and arms out to the sides. This helps to minimise feet entrapment and also to prevent head injuries.
Pinned
Boat and / or paddler is pinned to an obstacle.
Entrapment Drowning
Drowning where entrapment or being pinned underwater was the direct cause.
Flush Drowning
General term for an unknown drowning but usually thought to be due to a paddler being pinned underwater by the current even when wearing a PFD or due to the result of a long swim often in cold water. Older adults are more at risk.