Whitewater - AbsoluteAstronomy.com

Whitewater is formed in a rapid

Rapid

A rapid is a section of a river where the river bed has a relatively steep gradient causing an increase in water velocity and turbulence. A rapid is a hydrological feature between a run and a cascade. A rapid is characterised by the river becoming shallower and having some rocks exposed above the...

, when a river

River

A river is a natural watercourse, usually freshwater, flowing towards an ocean, a lake, a sea, or another river. In a few cases, a river simply flows into the ground or dries up completely before reaching another body of water. Small rivers may also be called by several other names, including...

's gradient

Stream gradient

Stream gradient is the grade measured by the ratio of drop in a stream per unit distance, usually expressed as feet per mile or metres per kilometre.-Hydrology and geology:A high gradient indicates a steep slope and rapid flow of water Stream gradient is the grade (slope) measured by the ratio of...

increases enough to disturb its laminar flow

Laminar flow

Laminar flow, sometimes known as streamline flow, occurs when a fluid flows in parallel layers, with no disruption between the layers. At low velocities the fluid tends to flow without lateral mixing, and adjacent layers slide past one another like playing cards. There are no cross currents...

and create turbulence

Turbulence

In fluid dynamics, turbulence or turbulent flow is a flow regime characterized by chaotic and stochastic property changes. This includes low momentum diffusion, high momentum convection, and rapid variation of pressure and velocity in space and time...

, i.e. form a bubbly, or aerated and unstable current; the frothy water appears white. The term is also used loosely to refer to less-turbulent but still agitated flows.

The term "whitewater" also has a broader meaning, applying to any river or creek itself that has a significant number of rapids. The term is also used as an adjective describing boating on such rivers, such as whitewater canoeing
Whitewater canoeing
Whitewater canoeing is the sport of paddling a canoe on a moving body of water, typically a whitewater river. Whitewater canoeing can range from simple, carefree gently moving water, to demanding, dangerous whitewater. River rapids are graded like ski runs according to the difficulty, danger or...

or whitewater kayaking
Whitewater kayaking
Whitewater kayaking is the sport of paddling a kayak on a moving body of water, typically a whitewater river. Whitewater kayaking can range from simple, carefree gently moving water, to demanding, dangerous whitewater. River rapids are graded like ski runs according to the difficulty, danger or...

.

Rapids

Four factors, separately or in combination, can create rapids: gradient, constriction, obstruction and flow rate. Gradient, constriction and obstruction are streambed topography factors and are relatively consistent. Flow rate is dependent upon both seasonal variation in precipitation and snowmelt and upon release rates of upstream dams.

Streambed topography

Streambed topography is the primary factor in creating rapids, and is generally consistent over time. Increased flow, as during a flood or high rainfall season can make permanent changes to the streambed by displacing rocks and boulders, by deposition of alluvium or by creating new channels for flowing water.

Gradient

The gradient

Stream gradient

of a river is the rate at which it loses elevation

Elevation

The elevation of a geographic location is its height above a fixed reference point, most commonly a reference geoid, a mathematical model of the Earth's sea level as an equipotential gravitational surface ....

along its course. This loss determines the river's slope, and to a large extent its rate of flow. Shallow gradients produce gentle, slow rivers while steep gradients are associated with raging torrents.

Constriction

Constriction is a method used by various snake species to kill their prey. Although some species of venomous and mildly-venomous snakes do use constriction to subdue their prey, most snakes which use constriction lack venom. The snake initially strikes at its prey and holds on, pulling the prey...

s can form a rapid when a river's flow is forced into a narrower channel. This pressure causes the water to flow more rapidly (hence the name) and to react differently to riverbed events (rocks, drops, etc.).

Obstruction

A boulder or ledge in the middle of a river or near the side can obstruct the flow of the river, and can also create a "cushion"; a "drop" (over the boulder); and "hydraulics" or "holes" where the river flows back on itself—perhaps back under the drop—often with fearful results for those caught in its grasp. (Holes, or hydraulics, are so-called because their foamy, aerated water provides less buoyancy and can feel like an actual hole in the river surface.) If the flow passes next to the obstruction, an eddy

Eddy (fluid dynamics)

In fluid dynamics, an eddy is the swirling of a fluid and the reverse current created when the fluid flows past an obstacle. The moving fluid creates a space devoid of downstream-flowing fluid on the downstream side of the object...

may form behind the obstruction; although eddies are typically sheltered areas where boaters can stop to rest, scout or leave the main current, they may be swirling and whirlpool-like. As with hydraulics (which pull downward rather than to the side and are essentially eddies turned at a 90-degree angle), the power of eddies increases with the flow rate.

In large rivers with high flow rates next to an obstruction, "eddy walls" can occur. An eddy wall is formed when the height of the river is substantially higher than the level of the water in the eddy behind the obstruction. This can make it difficult for a boater, who has stopped in that particular eddy, to reenter the river due to a wall of water that can be several feet high at the point at which the eddy meets the river flow.

Stream flow rate

A marked increase or decrease in flow can create a rapid (where previously wasn't one), "wash out" a rapid (decreasing the hazard) or make safe passage through previously-navigable rapids more difficult or impossible. Flow rate is typically measured in cubic metres per second (cumecs), or in cubic feet per second (cfs), depending on the country.

Classification of whitewater

The most widely used grading system is the International Scale of River Difficulty
International Scale of River Difficulty
The International Scale of River Difficulty is a standardized scale used to rate the safety of a stretch of river, or a single rapid. The grade reflects the technical difficulty and skill level required associated with the section of river...

, where whitewater (either an individual rapid, or the entire river) is classed in six categories from class I (the easiest and safest) to class VI (the most difficult and most dangerous). The grade reflects both the technical difficulty and the danger associated with a rapid, with grade I referring to flat or slow moving water with few hazards, and grade VI referring to the hardest rapids which are very dangerous even for expert paddlers, and are rarely run. Grade-VI rapids are sometimes downgraded to grade-V or V+ if they have been run successfully. Harder rapids (for example a grade-V rapid on a mainly grade-III river) are often portage
Portage
Portage or portaging refers to the practice of carrying watercraft or cargo over land to avoid river obstacles, or between two bodies of water. A place where this carrying occurs is also called a portage; a person doing the carrying is called a porter.The English word portage is derived from the...

d, a French term for carrying. A portaged rapid is where the boater lands and carries the boat around the hazard.

A rapid's grade is not fixed, since it may vary greatly depending on the water depth and speed of flow. Although some rapids may be easier at high flows because features are covered or "washed-out," high water usually makes rapids more difficult and dangerous. At flood stage, even rapids which are usually easy can contain lethal and unpredictable hazards (briefly adapted from the American version of the International Scale of River Difficulty).

Class 1: Very small rough areas, requires no maneuvering. (Skill Level: None)
Class 2: Some rough water, maybe some rocks, small drops, might require maneuvering. (Skill Level: Basic Paddling Skill)
Class 3: Whitewater, medium waves, maybe a 3–5 ft drop, but not much considerable danger. May require significant maneuvering. (Skill Level: Experienced paddling skills)
Class 4: Whitewater, large waves, long rapids, rocks, maybe a considerable drop, sharp maneuvers may be needed. (Skill Level: Whitewater Experience)
Class 5: Whitewater, large waves, continuous rapids, large rocks and hazards, maybe a large drop, precise maneuvering (Skill Level: Advanced Whitewater Experience)
Class 6: Whitewater, typically with huge waves, huge rocks and hazards, huge drops, but sometimes labeled this way due to largely invisible dangers (e.g., a smooth slide that creates a near-perfect, almost inescapable hydraulic (see 'Holes' below), as at Woodall Shoals or Chattooga
Chattooga River
The Chattooga River is the main tributary of the Tugaloo River. Its headwaters are located southwest of Cashiers, North Carolina, and it stretches to where it has its confluence with the Tallulah River within Lake Tugalo, held back by the Tugalo Dam...

). Class 6 rapids are considered hazardous even for expert paddlers using state-of-the-art equipment, and come with the warning "danger to life or limb." (Skill Level: Expert)

Features found in whitewater

On any given rapid there can be a multitude of different features which arise from the interplay between the shape of the riverbed and the velocity of the water in the stream.

Strainers

Strainers are formed when an object blocks the passage of larger objects but allows the flow of water to continue - like a big food strainer or colander

Colander

A colander is a bowl-shaped kitchen utensil with holes in it used for draining food such as pasta or rice.The perforated nature of the colander allows liquid to drain through while retaining the solids inside...

. These objects can be very dangerous, because the force of the water will pin an object or body against the strainer and then pile up, pushing it down under water. For a person caught in this position, it will be difficult or impossible to get to safety, often leading to a fatal outcome.

Strainers are formed by many different natural or man-made objects, like storm grates over tunnels, trees that have fallen into a river ("log jam"), bushes by the side of the river that are flooded during high water, wire fence, rebar from broken concrete structures in the water, or other debris. Strainers occur naturally most often on the outside curves of rivers where the current undermines the shore exposing the roots of trees and causing them to fall into the river forming strainers.

In an emergency it is often best to try and climb on top of a strainer so as not to be pinned against the object under the water. If you are in a river, swimming aggressively away from the strainer and into the main channel is your best bet. If you cannot avoid the strainer, you should swim hard towards it and try to get as much of your body up and over it as possible.

Sweepers

Sweepers are trees fallen in or heavily leaning over the river, still rooted on the shore and not fully submerged. Its trunk and branches may form an obstruction in the river like strainers. Since it is an obstruction from above, it often does not contribute to whitewater features but may create turbulence. In fast water sweepers can pose a serious hazard to paddlers.

Holes

Holes, or "hydraulics", (also known as "stoppers" or "souse-holes". See also Pillows), are formed when water pours over the top of a submerged object, or underwater ledges, causing the surface water to flow back upstream toward the object. Holes can be particularly dangerous—a boater may become stuck under the surface, in the recirculating water—or entertaining play-spots, where paddlers use the holes' features to perform various playboating

Playboating

Playboating is a discipline of whitewater kayaking or canoeing where the paddler performs various technical moves in one place , as opposed to downriver whitewater canoeing or kayaking where the objective is to travel the length of a section of river...

moves. In high & low volume water flow, holes can subtly aerate the water, enough to allow floating water craft to fall through the aerated water to the bottom of a deep 'hole'.

Some of the most dangerous types of holes are formed by low head dams (weir

Weir

A weir is a small overflow dam used to alter the flow characteristics of a river or stream. In most cases weirs take the form of a barrier across the river that causes water to pool behind the structure , but allows water to flow over the top...

s), and similar types of obstruction. In a low head dam, the 'hole' has a very wide, uniform structure - there's no escape point - and the sides of the hydraulic (ends of the dam) are often blocked by a man-made wall, making it impossible to paddle around, or slip off the side of the hydraulic, where the bypass water flow would become normal (laminar). By (upside-down) analogy, this would be much like a surfer slipping out the end of the pipeline, where the wave no longer breaks. Low head dams are insidiously dangerous because their danger cannot be easily recognized by people who have not studied swift water. (Even 'experts' have died in them.) Floating debris (trees, kayaks, etc.) is often trapped in the retro-flow 'grinder' for weeks at a time.

Refs: NFPA-1006 Standard for Technical Rescuer, Swiftwater rescue

Swiftwater rescue

Swiftwater rescue is a subset of technical rescue dealing in whitewater river conditions. Due to the added pressure of moving water, swiftwater rescue involves the use of specially trained personnel, ropes and mechanical advantage systems that are often much more robust than those used in standard...

, Canyoning

Canyoning

Canyoning is traveling in canyons using a variety of techniques that may include other outdoor activities such as walking, scrambling, climbing, jumping, abseiling, and/or swimming....

Waves

Wave

In physics, a wave is a disturbance that travels through space and time, accompanied by the transfer of energy.Waves travel and the wave motion transfers energy from one point to another, often with no permanent displacement of the particles of the medium—that is, with little or no associated mass...

s are formed in a similar nature to hydraulics and are sometimes also considered hydraulics as well. Waves are noted by the large smooth face on the water rushing down. Sometimes a particularly large wave will also be followed by a "wave train", a long series of waves. These standing wave

Standing wave

In physics, a standing wave – also known as a stationary wave – is a wave that remains in a constant position.This phenomenon can occur because the medium is moving in the opposite direction to the wave, or it can arise in a stationary medium as a result of interference between two waves traveling...

s can be smooth or, particularly the larger ones, can be breaking waves (also called "whitecaps" or "haystacks").

Because of the rough and random pattern of a riverbed, waves are often not perpendicular to the river's current. This makes them challenging for boaters since a strong sideways or diagonal (also called " a lateral") wave can throw the craft off.

In fluid mechanics, waves are classified as laminar, but the whitewater world has also included waves with turbulence ("breaking waves") under the general heading of waves.

Pillows

Pillows are formed when a large flow of water runs into a large obstruction, causing water to "pile up" or "boil" against the face of the obstruction. Pillows can be dangerous because sometimes the object that forms the pillow is undercut and so paddlers can be swept underwater - possibly to be entrapped. Pillows are also known as "pressure waves".

Eddies

Eddy (fluid dynamics)

are formed, like hydraulics, on the downstream face of an obstruction. Unlike hydraulics, eddies swirl on the horizontal surface of the water. Typically, they are calm spots where the downward movement of water is partially or fully arrested - a nice place to rest or to make one's way upstream. However, in very powerful water, eddies can have powerful, swirling currents which can flip boats and from which escape can be very difficult.

Undercut rocks

Undercut rocks are rocks that have been worn down underneath the surface by the river, or loose boulders which cantilever out beyond their resting spots on the riverbed. They can be extremely dangerous features of a rapid because a person can get trapped underneath them underwater. This is especially true of rocks that are undercut on the upstream side. Here, a boater may become pinned against the rock underwater. Many whitewater deaths have occurred in this fashion. Undercuts sometimes have pillows, but other times the water just flows smoothly under them, which can indicate that the rock is undercut. Undercuts are most common in rivers where the riverbed cuts through sedimentary rocks like limestone

Limestone

Limestone is a sedimentary rock composed largely of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate . Many limestones are composed from skeletal fragments of marine organisms such as coral or foraminifera....

rather than igneous rock

Igneous rock

Igneous rock is one of the three main rock types, the others being sedimentary and metamorphic rock. Igneous rock is formed through the cooling and solidification of magma or lava...

like granite

Granite

Granite is a common and widely occurring type of intrusive, felsic, igneous rock. Granite usually has a medium- to coarse-grained texture. Occasionally some individual crystals are larger than the groundmass, in which case the texture is known as porphyritic. A granitic rock with a porphyritic...

. In a steep canyon, the side walls of the canyon can also be undercut.

A particularly notorious undercut rock is Dimple Rock, in Dimple Rapid on the Lower Youghiogheny River

Youghiogheny River

The Youghiogheny River , or the Yough for short, is a tributary of the Monongahela River in the U.S. states of West Virginia, Maryland, and Pennsylvania...

, a very popular rafting and kayaking river in Pennsylvania. Of about nine people that have died at or near Dimple Rock, including three in 2000, several of the deaths were the result of people becoming entrapped after they were swept under the rock.

Sieves

Another major whitewater feature is a sieve, which is a narrow empty space that water flows through between two obstructions, usually rocks. Similar to strainers, water is forced through the sieve, resulting in higher flow velocity which forces water up and creates turbulence.

Whitewater craft

There are many different types of whitewater craft that people use to make their way down a rapid, preferably with finesse and control. Here is a short list of them.

Whitewater kayaks differ from sea kayaks and recreational kayaks in that they are better specialized to deal with moving water. They are often shorter and more maneuverable than sea kayaks and are specially designed to deal with water flowing up onto their decks. Most whitewater kayaks are made of plastics these days, although some paddlers (especially racers

Whitewater racing

Wildwater canoeing is a competitive discipline of canoeing in which kayaks or Canadian canoes are used to negotiate a stretch of river speedily...

and "squirt boaters") use kayaks made of fiberglass composites. Whitewater kayaks are fairly stable in turbulent water, once the paddler is skillful with them; if flipped upside-down, the skilled paddler can easily roll them back upright. This essential skill of whitewater kayaking is called the "Eskimo Roll", or simply "Roll." Kayaks are paddled in a low sitting position (legs extended forward), with a two-bladed paddle. See Whitewater kayaking

Whitewater kayaking

Whitewater kayaking is the sport of paddling a kayak on a moving body of water, typically a whitewater river. Whitewater kayaking can range from simple, carefree gently moving water, to demanding, dangerous whitewater. River rapids are graded like ski runs according to the difficulty, danger or...

.

Raft
Raft
A raft is any flat structure for support or transportation over water. It is the most basic of boat design, characterized by the absence of a hull...

s are also often used as a whitewater craft; more stable than typical kayaks, they are less maneuverable. Rafts can carry large loads, so they are often used for expeditions. Typical whitewater rafts are inflatable craft, made from high strength fabric coated with PVC, Urethane, Neoprene or Hypalon; see rafting

Rafting

Rafting or white water rafting is a challenging recreational outdoor activity using an inflatable raft to navigate a river or other bodies of water. This is usually done on white water or different degrees of rough water, in order to thrill and excite the raft passengers. The development of this...

. While most rafts are large multi-passenger craft, the smallest rafts are single-person whitewater craft, see packraft

Packraft

Packraft and trail boat are colloquial terms for a small, portable inflatable boat designed for use in all bodies of water, including technical whitewater and ocean bays and fjords. A packraft is designed to be light enough to be carried for extended distances...

.

Catarafts are constructed from the same materials as rafts. They can either be paddled or rowed with oars. A specialized cataraft, designed without any metal frame, is a Shredder. It was invented in 1982 by Tom Love and is manufactured by his company Airtight Inflatables in Ohiopyle, Pa. A Shredder is specifically designed to be paddled. It is usually paddled by a two person crew, though highly skilled paddlers are able to negotiate extreme whitewater in a Shredder paddled as a solo boat. Typical catarafts are constructed from two inflatable pontoons on either side of the craft that are bridged by a frame. Oar-propelled catarafts have the occupants sitting on seats mounted on the frame. Virtually all oar-powered catarafts are operated by a boatsman with passengers having no direct responsibilities. Catarafts can be of all sizes; many are smaller and more maneuverable than a typical raft.

Canoe
Canoe
A canoe or Canadian canoe is a small narrow boat, typically human-powered, though it may also be powered by sails or small electric or gas motors. Canoes are usually pointed at both bow and stern and are normally open on top, but can be decked over A canoe (North American English) or Canadian...

s are often made of fiberglass, kevlar, plastic or a combination of the three for strength and durability. They may have a spraycover, resembling a kayak, or be "open," resembling the typical canoe. This type of canoe is usually referred to simply as an "open boat." Whitewater canoes are paddled in a low kneeling position, with a one-bladed paddle. Open whitewater canoes often have large airbags and in some cases foam, usually 2 lb density ethyl foam, firmly attached to the sides, to displace water in the boat when swamped by big waves and holes and to allow water to be spilled from the boat while still in the river by floating it up on its side using the foam and bags. Like kayaks, whitewater canoes can be righted after capsizing with an Eskimo Roll; however this requires more skill in a canoe.

C1s are similar in construction to whitewater kayaks. However, they are paddled in a low, kneeling position. They employ the use of a one-blade paddle, usually a little shorter than used in a more traditional canoe. They will have a spraycover, essentially the same type used in kayaking. Like kayaks, C1s can be righted after capsizing with an Eskimo Roll.

McKenzie River dory
McKenzie River dory
The McKenzie dory or Rogue River dory also called by many a Drift Boat is an evolution of the open-water dory, converted for use in rivers. The design is characterized by a wide, flat bottom, flared sides, a narrow, flat bow, and a pointed stern. The sole identifying characteristic of the McKenzie...

or "Drift Boat" by some. A more traditional "hard sided" boat. The design is characterized by a wide, flat bottom, flared sides, a narrow, flat bow, a pointed stern, and extreme rocker in the bow and stern to allow the boat to spin about its center for ease in maneuvering in rapids.

River bugs are small single person inflatable craft where a person's feet stick out of one end. River Bugging

River Bugging

River Bugging is a whitewater sport where a single person navigates a stretch of river in a craft known as a river bug. The river bug is a small inflatable craft with an inflatable tube at each side of the user and an inflatable back rest behind. The user sits between the tubes and can be secured...

is done feet first with no paddle.

Safety

Running whitewater rivers is a popular recreational sport but is not without danger. In fast moving water there is always the potential for injury or death by drowning or hitting objects. Fatalities do occur; some 50 people die in whitewater accidents in the United States each year.

Strainers and sieves can pose a particular hazard. If the sieve is visible above water, a boater can be pinned against it and may eventually be forced underwater as the current passes through. If the sieve is completely submerged, it is especially insidious because it may not be discernible at all. In shallow water, bows of boats can get caught in submerged sieves, as the current pulls the nose down below the rocks where it can lodge. If this happens, it is likely that the whole boat will get pulled under water. Sieves pose a particular hazard to swimmers because even the smallest sieves can trap a person's foot if they stand up in the current. The force of the current then pushes the whole body underwater, becoming a deadly situation in a matter of seconds. It is for this reason that one of the first things whitewater boaters learn is never to stand up in more than ankle deep water where there is a current.

The dangers can be mitigated (but not eliminated) by training, experience, scouting, the use of safety equipment (such as personal flotation device

Personal flotation device

A personal flotation device is a device designed to assist a wearer, either conscious or unconscious, to keep afloat.Devices designed and approved by authorities for use by...

, helmet, throw ropes), and using other persons as "spotter

Spotter

A spotter is someone trained to look for something. The term has the following special meanings.*Weather spotter, an individual who observes the weather to inform other groups.*Storm spotter, a weather spotter who observes specific weather events....

s".

Scouting or examining the rapids before running them is crucial to familiarize oneself with the stream and anticipate the challenges. This is especially important during flood conditions when the highly increased flow have altered the normal conditions drastically.