As seen from http://www.paddling.net/guidelines/showArticle.html?67
Classification of Rapids, Water Level, and Canoeists
By I. Herbert Gordon
Part of the planning of a canoe trip entails knowing what to expect on your trip. This is not so difficult to figure out when you are canoeing on a lake. For canoeing on a river, however, you should learn about the ratings given to rapids, water level, and even canoeists.
Rapids
A skier is aware that a black diamond run is a lot steeper and more difficult than a green circle slope. Rapids, like ski slopes, vary in their intensity. The International Rating system classifies rapids as follows:
* Class A: Lake water. Still. No perceptible movement. met. Even nor
* Class I.- Easy. Smooth water; light riffles; clear passages, occasional sand banks and gentle curves. The most difficult problems might arise when paddling around bridges and other obvious obstructions. classification
* Class II.- Moderate. Medium-quick water; rapids with regular waves; clear and open passages between rocks and ledges. Maneuvering required. Best handled by intermediates who can maneuver canoes and read water.
* Class III.- Moderately difficult. Numerous high and irregular waves; rocks and eddies with passages clear but narrow and requiring experience to run. Visual inspection required if rapids are unknown. Open canoes without flotation bags will have difficulty. These rapids are best left to canoeists with expert skills.
* Class IV- Difficult. Long and powerful rapids and standing waves; souse holes and boiling eddies. Powerful and precise maneuvering required. Visual inspection mandatory. Cannot be run in canoes unless the craft is decked or properlyequipped with flotation bags. Advance preparations for possible rescue work important.
* Class V- Extremely difficult. Long and violent rapids that follow each other almost without interruption. River filled with obstructions. Big drops and violent currents. Extremely steep gradient. Even reconnoitering may be difficult. Rescue preparations mandatory. Can be run only by top experts in specially equipped whitewater canoes, decked craft, and kayaks.
* Class VI.- Extraordinarily difficult. Paddlers face constant threat of death because of extreme danger. Navigable only when water levels and conditions are favorable. This violent whitewater should be left to paddlers of Olympic ability. Every safety precaution must be taken.
Water Level
The characteristics of a river can change remarkably as the water level rises or falls. As you might expect, a set of Class II rapids can become raging Class IV when the water is abnormally high following spring runoff or heavy storms. Conversely, a Class IV can turn into a shallow pussycat when the water level is low in the late summer. Even normally calm stretches become turbulent and dangerous at flood stage, because the force of currents slammed this way and that by rocks and obstructions creates powerful and dangerous surface conditions.
An International Rating system has also been devised to describe river flow. The classification for a specific river may change from season to season; the following letter designations are used to describe water level and rate of flow:
* L, or Low. Below-normal levels for the river. Below-normal depth may interfere with good paddling. Shallows may turn into dry banks and low areas become muddy sandbars.
* M, or Medium. Normal river flow. Medium water generally is used to describe good water for rivers with slight gradients and enough depth for passage on the steeper sections.
* MH, or Medium High. Higher than normal. Faster flow on gentle gradients. The best flow for more difficult river sections with enough water for passage over low ledges and through rock gardens.
* H, or High. Water is becoming difficult to handle. he river is well above normal stage. Canoeists may refer to the strong currents as "heavy." Small debris may come floating by, a warning that the river is dangerous and better left to skilled kayakers or canoeists whose craft are supported by flotation bags.
* HH, or High-High. Very heavy water. Hydraulics are complex. Even slight gradients become treacherous. Debris frequent. Only for experts.
* F, or Flood. Abnormally high water, overflowing the banks; current extremely violent; low-lying areas underwater. TV crews show up to shoot tape for the evening news. Not for any boaters except those with appropriate equipment on dangerous rescue missions.
Canoeists
The Appalachian Mountain Club rates canoeists on a scale of I through V. Check your competence against their ratings:
* Class I.- Beginner. Is familiar with basic strokes and can handle a tandem canoe competently from the bow or stern in flat water; solo canoeist is familiar with basic strokes.
* Class II.- Novice. Can handle more advanced whitewater strokes solo or in either bow or stern of a tandem canoe. Knows how to read water; can negotiate easy and regular rapids with assurance.
* Class III.- Intermediate. Can negotiate rapids requiring linked sequence of maneuvers; understands and can use eddy turns and basic bow-upstream techniques; is skilled in either bow or stern of a tandem canoe; can paddle Class II rapids in a solo canoe or kayak.
* Class IV- Expert. Has established ability to run difficult (Class III and Class IV) rapids in bow or stern of a tandem craft; can paddle solo in a properly equipped canoe or kayak; understands and can maneuver in heavy (Class H) water.
* Class V- Leader. Is an expert canoeist; possesses the experience, judgment, and training to lead a group of any degree of skill on any navigable waterway and in the wilderness.
To the preceding list I would add a "Class A" to describe one who has virtually no familiarity with canoes or canoeing.
Should You Paddle That River?
Three elements must be evaluated before you are competent to judge your ability to handle a river: (1) your ability; (2) the class of rapids; and (3) the river flow level. You should have no trouble deciding whether you should paddle an unknown 12-mile stretch of the Foamy River when a friend tells you:
"The first couple of miles are sort of flat, but then you'll run into five or six sets of Class II rapids just after you pass the old covered bridge on Route 6. There's a rock garden after the river swings past the only island you'll find on your trip. After that it's clear sailing, but the river normally runs pretty fast for the last 2 miles. Of course, you gotta keep in mind we've had a lot of rain the past two weeks, and I know before that the river was running maybe a little below Medium, but it could be Medium-High right now. If it is, you can run a set of ledges to the left of the island. Otherwise, stick to the right. And that rock garden might be a Class III set of rapids, a helluva lot of fun-it's usually just a lot of maneuvering.
A helluva lot of fun is right, that is, if you and your partner have the experience to handle this kind of water.
The moral: Know what to expect from a technical description of a river and from your own skill at the class of rapids and expected water level. Don't put yourself and your partners at risk. If in doubt, personally inspect the river first, or don't run it.
Canoe livery operators are excellent sources of information about the rivers they service and usually are quick to warn customers about any unusual situations. When the waters are dangerous because of high levels or unusual cold temperatures, most operators will cancel all rentals. The better ones will give out rain checks. Even if you have your own canoe, operators will be as ready to warn you about dangerous conditions as they are their own customers.
Excerpted: The Complete Book of Canoeing by I. Herbert Gordon -Falcon Publishing.
