I have been a commercial river guide for 18 years and the guests that I have taken down the multiple rivers I have worked ask a variety of questions. One of the most common questions is why do they call it “White Water”? I have always explained how the gradient drop makes the water move faster, rocks (or objects) in the river direct the current, and the turbulence makes the water bubbly (which makes the water appear white).
Well one night while surfing the web I typed in “white water” on Wikipedia and learned a few things. Check out some of the content.
From Wikipedia, the free encyclopedia
(Redirected from White water)
Whitewater is formed in a rapid, when a river‘s gradient increases enough to disturb its laminar flow and create turbulence, 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 or whitewater kayaking.
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.
1. 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.
The gradient of a river is the rate at which it loses elevation 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.
Constrictions 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.).
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 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 pulldownward 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
Main article:International Scale of River Difficulty
The most widely used grading system is the International Grading System, 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 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).
- 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, as at Woodall Shoals/Chattooga). 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)
Section 9 of the French Broad River goes up to Class IV rapids and is a great river for beginners and experts.