International Scale of River Difficulty
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The International Scale of River Difficulty is a standardized scale used to rate the safety of a stretch of river, usually a single rapid. The grade reflects both the technical difficulty and the danger associated with a rapid.
Classification
- Class I - Easy
- * fast water with ripples or waves
- * all dangers are obvious, negligible risk to swimmers, easy self-rescue
- Class II - Novice
- * straightforward rapids with regular waves
- * easy to medium drop-offs(chutes, ledges, falls)
- * eddies and shear zones are easily negotiated
- * best passage evident without scouting
- Class III - Intermediate
- * rapids with moderate, irregular waves, breakers, rollers and back eddies
- * upper limit for canoes without spray cover
- * scouting in advance is advised for inexperienced parties
- Class IV - Advanced
- * high, irregular waves, breakers, powerful back eddies, whirlpools and sharp bends
- * powerful but predictable rapids requiring precise handling in difficult water, for experienced paddlers only
- * moderate to high risk to swimmers, group rescue is often required
- * advance scouting is required
- * spray skirt/cover, helmet, PFD and hull floatation aids mandatory
- Class V - Expert
- * extremely long and/or violent rapids, often containing large, unavoidable obstacles, holes, steep banks, and turbulent water
- * very fast currents with powerful whirlpools and boiling back eddies
- * rescue is often difficult for experts
- * advance scouting may be difficult
- Class VI - Extreme
- * upper limit of present-day skills and equipment and only for teams of experts, taking all safety precautions
- * unexplored or uncharted rapids where navigation may be very difficult to impossible.
- * Luck often considered an important part of a successful negotiation.
Caution in application
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. Conversely, some rapids may be easier with lower water levels when dangerous hydralics become easier to manage.Also, some rivers with huge volumes of fast moving water may require little manouevering, but will pose serious risk of injury or death in the event of a capsize.
Nevertheless, the application of this classification can vary enormously, depending on the perception, skill level, experience, and bravery or foolhardiness of the paddler. And they can 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.
See also
External links
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