River Grade / Classifications

Classification

There are six levels, each commonly referred to as "Grade" or "Class" and then a number. The scale is not linear, nor is it fixed. There can be hard grade twos, easy grade threes, and so on. Also, the grade of a river may 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. Even though a section of river may be given an overall grading, it may contain sections above that grade (these are often noted as features and details of portages may be given). Conversely, a higher grade will likely contain sections of lower graded water.

Class/Grade I

A Grade I (One) section will have long sections of flat, slow moving water, with minor ripples or waves and a course that is easily navigable. There is little danger to swimmers (other than the usual hazards of water) and self-rescue should be easy.

Class/Grade II

A Grade II (Two) section may have sections of straightforward rapids, some small waves, weirs, small drops or ledges and eddies. There will be a clear route through all features without a need for inspection.

Class/Grade III

A Grade III (Three) section will have numerous rapids, irregular waves and moderate drops, harder eddies that may recirculate and stoppers (also known as hydraulics or holes) may form below drops and in waves. The river may have a broken flow that might not always present a clear course. Often these sections have a series of drops creating a steep overall gradient. On the whole, from-the-water inspection should be sufficient, although some harder parts may need inspection from the river bank. The "Pine Creek" section of the Arkansas River, Class IV-V The "Pine Creek" section of the Arkansas River, Class IV-V

Class/Grade IV

A Grade IV (Four) section will feature long, difficult rapids with highly irregular waves, a steep gradient, a stepped profile with drops up to 3 m in height, difficult eddies and whirlpools. The course of the river may be hard to recognise and powerful but predictable flows require precise handling, with a high risk to swimmers. Off-river inspection is highly advised, as is bank support for some features.

Class/Grade V

A Grade V (Five) section will be similar to a Grade IV, with larger, more violent features and less predictable flows. Often, there will be large, unavoidable dangers such as holes and boiling/recirculating eddies. Courses are difficult to find and will definitely incur a risk to both paddler and equipment. A pre-run inspection from the river bank is vital. Rescue is often difficult, and bank support with throw lines is always recommended.

Due to advances in what is runnable in recent years, many rapids are being revised from class 6 to class 5. Because of this, some boaters have began describing certain rapids as class 5.0, 5.1, 5.2, etc., each being equivalent to a higher class level. This provides additional information about the difficulty of a rapid, while preserving the special function of the class 6 category.[1]

Class/Grade VI

A Grade VI (Six) section is at the pinnacle of technicality and difficulty. Only to be attempted by teams of highly skilled experts, there is a definite risk to a paddler's life, as many of these sections have either never been (successfully) paddled before, or they have led to deaths. Often a Grade VI will be a single feature within a Grade IV or V section, such as a water fall. Bank support with rescue lines is always required, as is inspection from all possible angles.

References

*Lee Belknap, American Whitewater: Upgrading the American Version of the International Scale of River Difficulty

*American Whitewater: International Scale of River Difficulty