Addison’s Scale for Rivers

Addison’s Scale for Rivers

A Carolina Paddler Article

by Alton Chewning

-Corran Addison has been around paddling and other adventure sports for many years.  Originally from South Africa, Addison has paddled in many countries and for a while spent time in the US Southeast.  Along the way he decided the common I-VI system of rating rivers felt inadequate and led to confusion in discussing rivers and rapids.  Specifically, it led to misunderstandings about the technical difficulty of a rapid versus the consequences if something goes wrong.

The primary scale used worldwide is the International Scale of River Difficulty or ISRD. The US uses a slightly different American version.  The ratings work on a 1-6 scale, and like in Super Bowl designations, they use Roman numerals.

International Scale of River Difficulty

Class I Easy

Easy difficulty with low consequences.  Smooth water with a clear passage through slight current or ruffles; can have gentle curves.  No gradient loss. No hazards present or maneuvering required.

Class II Novice

Moderate difficulty with low consequences.  Moving water with identifiable rapids and regular waves; clear passages exist between rocks and hazards.  Minimal gradient loss.  Some maneuvering is required.

Class III Intermediate

Moderate difficulty and some consequences. Fast water with standing waves; rocks, eddies and hazards exist with clear passages through narrower channels.  Some gradient loss.  Maneuvering is required.

Class IV  Advanced

Hard, with major consequences.  Long and/or powerful rapids with dynamic features; rocks, recirculating hydraulics, boiling eddies and other hazards.  Significant gradient loss.  Precise maneuvering required.

Class V  Expert

Very hard, with major consequences. Long and powerful rapids with dynamic features; rocks, recirculating hydraulics, boiling eddies and other hazards.  Substantial and continuous gradient loss. Exact maneuvering required.

Class VI Expert Plus

Previously considered un-navigable rapids. Unavoidable hazards and extreme consequences.  Substantial gradient loss.

The International Scale of River Difficulty is very good but does not address every circumstance.  One can go to the American Whitewater website to read the various elaborations added to the basic ratings scale to address these shortcomings. 

Addison’s Scale

Addison formulated a new scale, one that provides separate ratings for the three major criteria in running a river: difficulty, danger and exposure or accessibility.  Addison’s Scale thus has three placeholders, for example, 3/5B or 4/3A, to classify a rapid or river.

Difficulty:  The scale uses the familiar 1-6 for difficulty (although this could be considered open-ended as innovations in gear and techniques lead to running more difficult rapids.  For instance there could be a 7, 8, 9.)  What basic boat-handling skills are needed to negotiate this rapid or river.

Danger:  Also uses a 1-6 scale.  What are the consequences (a term the ISRD uses frequently) of a paddling mistake – a missed move or line?

Exposure:  This is classified as A, B or C.  What is the accessibility to help?  How quickly can safety or medical assistance be brought to bear.  Is the location remote or otherwise inaccessible or can it be easily reached by qualified responders.  What is the quality and capability of rescue and medical care available?

So, in Addison’s Scale, a rapid with several difficult technical moves followed by a large pool with lots of access, say, the Charlotte White Water Center’s Competition course, could be a 4/2A.  The same course plopped down in a South American jungle could be a 4/2B or 4/2C.

What would Addison rate Niagara Falls?  “Any fool can paddle over it, but your chances of survival are slim. On the flip side, help is right there. That’s a nice little 2/6A.”

The ISRD and Addison’s Scale systems are both useful in discussing rivers and their runnability.  They essentially build on each other in addition to all the other sources of information we have about a river or a rapid.  Sometimes we can be burdened by so much data; then again, our wonderful, adventurous sport does have some inherent danger and we should be prepared.  In future articles in Carolina Paddler we’ll refer back to these scales.

Please refer to the sources below for more detailed explanations and examples.

Sources:

–Addison’s Scale of Difficulty Video

https://www.soulwaterman.com/blogs/news/addisons-scale-river-rating-system

–American Whitewater website, “international Scale of River Difficulty.”

https://www.americanwhitewater.org/content/Wiki/safety:internation_scale_of_river_difficulty

–Paddler Magazine, “Addison’s Scale”  by Corran Addison

https://paddlerezine.com/addisons-scale/

–Paddler Magazine, “Difficulty Demystified: A Modern Guide to the Rapid Ratings Scale” by Kalob Grady

https://paddlingmag.com/stories/isrd-rapids-rating-scale/

–Interview with Corran Addison, January 11, 2024.