Whitewater is formed in a rapid when a river’s gradient increases enough to create so much turbulence that air is entrained into the water body, that is, it forms a bubbly or aerated and unstable current; the frothy water appears white. The term is also loosely used 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 or whitewater kayaking.
Fast rivers
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
Classification
The most widely used grading system is the where white water 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 portaged, 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.
Whitewater craft
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 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.
Rafts 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 an inflatable craft, made from high strength fabric coated with PVC, Urethane, Neoprene or Hypalon; see rafting. While most rafts are large multi-passenger craft, the smallest rafts are single-person whitewater craft, see pack rafts. Rafts sometimes have inflatable floors, with holes around the edges, that allow water that splashes into the boat to easily flow to the side and out the bottom these are typically called “self-bailers” because the occupants don’t have to “bail” water out with a bucket. Others have simple fabric floors, without any way for water to escape, these are called “bucket boats”, both for their tendency to hold water like a bucket, and because the only way to get water out of them is by bailing with a bucket.
Catarafts are constructed from the same materials as rafts. They can either be paddled or rowed with oars. Typical catarafts are constructed from two inflatable pontoons on either side of the craft that is 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 draft.
Canoes are often made of fiberglass, kevlar, plastic or a combination of the three for strength and durability. They may have a spray cover, 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-bladed paddle, usually a little shorter than used in a more traditional canoe. They will have a spray cover, essentially the same type used in kayaking. Like kayaks, C1s can be righted after capsizing with an Eskimo Roll.
McKenzie River dory 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 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, helmet, throw ropes, and using other persons as “spotters”.
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 has altered the normal conditions drastically.
Sources – Wikipedia
