River Classification Ratings
There are six categories, each referred to as grade or class followed by a number. Float Idaho is structured to only paddle class 1 up to 3. The scale is not linear, nor is it fixed. For instance, there can be difficult grade two’s, easy grade three’s, and so on. The grade of a river may (and usually does) change with the level of flow. Often a river or rapid will be given a numerical grade, and then a plus (+) or minus (-) to indicate if it is in the higher or lower end of the difficulty level. Know that what should be an easy class 1 can dangerously turn into a 2 or 3 with downed trees and debris in the river. The Boise River, in particular, is unpredictable (as are most rivers) so error on the side of caution as downed trees and serious obstacles are common throughout the river.
While a river section may be given an overall grading, it may contain sections above that grade, often noted as features, or conversely, it may contain sections of lower graded water as well.
The grade of a river or rapid is likely to change along with the level of the water. High water usually makes rapids more difficult and dangerous, although some rapids may be easier at high flows because features are covered or washed out. At spate/flood stage, even rapids which are usually easy can contain lethal and unpredictable hazards. Conversely, some rapids may be easier with lower water levels when dangerous hydraulics become easier to manage. Some rivers with high volumes of fast moving water may require little maneuvering, but will pose serious risk of injury or death in the event of a capsize. The bottom line, river classification is not an exact science and rivers are simply unpredictable. Even sections you may have paddled many times before can turn into something quite different. Expect the unexpected, which is part of the fun of the sport.
A summary of river classifications as presented by the American Whitewater Association:[1]
Class I:
Easy
Fast moving water with riffles and small waves. Few obstructions, all obvious and easily missed with little training. Risk to swimmers is slight; self-rescue is easy.
Class II:
Novice
Straightforward rapids with wide, clear channels which are evident without scouting. Occasional maneuvering may be required, but rocks and medium-sized waves are easily avoided by trained paddlers. Swimmers are seldom injured and group assistance, while helpful, is seldom needed. Rapids that are at the upper end of this difficulty range are designated Class II+.
Class III:
Intermediate
Rapids with moderate, irregular waves which may be difficult to avoid and which can swamp an open canoe. Complex maneuvers in fast current and good boat control in tight passages or around ledges are often required; large waves or strainers may be present but are easily avoided. Strong eddies and powerful current effects can be found, particularly on large-volume rivers. Scouting is advisable for inexperienced parties. Injuries while swimming are rare; self-rescue is usually easy but group assistance may be required to avoid long swims. Rapids that are at the lower or upper end of this difficulty range are designated Class III- or Class III+ respectively.
