International Scale of River Difficulty
From Wikipaddle
The International Scale of River Difficulty is a standardized scale used to rate the safety of a stretch of river, or a single rapid. The grade reflects the technical difficulty, skill level required and danger associated with the section of river.
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Classification
There are six levels, each commonly referred to as "Class" or "Grade" and then a number, most commonly in Roman numeral form (eg. II, IV, etc.), but standard decimal or spoken form (1, 2, Three, Four, etc.) are also used commonly. The scale is not linear, nor is it fixed. There can be hard Grade Two's, easy Grade Three's, and so on. Often a river or feature 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 spectrum.
The grade of a river or section can change dramatically with water levels, and inspection on the day is always recommended. Don't rely on us, a guidebook or your own experience to always be accurate, rivers change.
It should be noted that even though a section of river may be given an overall grading, it may contain one or two sections above that grade. These noted features in guides and details of portages may be given. Sometimes when grading a section a higher number will be given in brackets, eg: "Grade: 2-3 (4)", which signifies that there are a few feature or section at that higher grade. Conversely, a high grade river will most likely contain several sections of lower graded water in between the main features, however it is taken for granted that this is the case and should not be used to "dilute" or lower the overall grade of a river.
Class I / Grade 1
A Grade I (One) section will have long sections of regular moving water, with minor rapids and/or regular waves. Any obstructions should be noticeable and easily avoided, and navigation should generally be clear.
Class II / Grade 2
A Grade II (Two) section may have sections of straightforward rapids, some irregular waves, weirs, very small drops or ledges which may have small stoppers underneath. Eddys should be well defined but relatively calm. The flow of water will be irregular, but there will be a clear route through all features without a need for bank inspection and obstructions should be avoidable.
Class III / Grade 3
A Grade III (Three) section will have numerous rapids varying in length, with irregular waves and small drops. Eddys may be harder to hit and might recirculate. Hydraulics / stoppers may form below features. The river may have a broken flow that might not always present a clear course, with multiple obstructions, small boulders and pressure waves forming. 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.
Class IV / Grade 4
A Grade IV (Four) section will feature long, difficult and continuous rapids with highly irregular waves, a steep gradient, a stepped profile with drops up to 3m in height. Eddys may be difficult to hit and may recirculate or form whirlpools. The course of the river may be hard to recognise with multiple obstructions to the flow, which will be powerful but predictable, requireing precise handling of boats, and will present a high risk to swimmers. Off-river inspection is highly advised, as is bank support along and below features.
Class V / Grade 5
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 or recirculating eddys. Courses are difficult to find and will definitely incur a risk to both he paddler and their equipment. A pre-run inspection from the river bank is VITAL. Rescue is often difficult, and bank support with throw lines is always recommended.
Class VI / Grade 6
A Grade VI (Six) section is at the pinnacle of technicality and difficulty, and are considered yb many to be technically impossible to all but the most 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. Luck is often considered an important part of a successful run.
Caution in application
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 flood stage (spate), 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.
Also, 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.
Additionally, the application of this classification can vary enormously, depending on the skill level, experience, bravery or foolhardiness of the paddlers who rated the river. Ratings can also differ somewhat from country to country.
Other classifications
The grading system in Australia and New Zealand is as follows:
- Small regular waves. Easy passage, but care may be needed with obstacles.
- Regular medium sized waves and generally unobstructed passage.
- Fairly high waves, and the passage may be difficult to recognise from on the river.
- High, powerful, irregular waves, with the passage often difficult to recognise.
- Very difficult rapids; the extreme for commercial operations.
- Very dangerous, and at the limit of practicality.
