International Scale of River Difficulty
The International Scale of River Difficulty is the American Whitewater version of the rating system used to compare river difficulty worldwide. The scale is not exact. Rivers do not always fit easily into one category, and regional or individual interpretations may cause misunderstandings. It is not a substitute for a guidebook, first-hand descriptions of a run, or other sources of river information. As river difficulty increases, the danger becomes more severe. As rapids become longer and more continuous, the challenge increases. Running an occasional Class IV rapid on a stretch of river is less consequential than dealing with an entire river run of this category.
source: American Whitewater
Whitewater Classification Applied to Triad River Tours Popular Rafting Sections
Sauk River/Sauk2 (high water; 4,000-7000 cfs)
Classification: 4
Sauk River/Sauk2 (medium water; 2500-4,000 cfs)
Classification: 3+
Sauk River/Sauk2 (low water; 800-2500 cfs)
Classification: 3+
Snoqualmie River/Sno2 (high water; 2400-5000 cfs)
Classification: 4
Snoqualmie River/Sno2 (low water; 1200-2400 cfs)
Classification: 3+
Skykomish River/Sky1 (high water; above 5,000 cfs)
Classification: 5-
Skykomish River/Sky1 (low water; below 2500 cfs)
Classification: 4
Skagit River/SK5 (low water; below 8,000 cfs)
Classification: 3-
Risk Formula
Years ago an article in Paddler Magazine brought to the surface the need for more logical and data driven conclusions to be drawn for whitewater river runners. The Risk Formula (probability x consequences) was adopted. This system is utilized by our staff as part of our extensive risk analysis for all river protocols. Here is a diagram showing how it works. Note that the X-axis (horizontal) measures severity, while the Y-axis (vertical) measures probability. Taking these two into account through multiplication, a new variable emerges as the total risk factor of a river as it relates to the probability and severity of physical harm to an individual.
Note: There is no calculation regarding psychological harm involved in risk classification. This is perhaps the most subjective measurement of all and is most challenging to quantify. We should not disregard the magnitude of the after effects of trauma associated with river incidents, especially with children, who may be more survivable in most whitewater accidents, but who typically suffer more psychological trauma and sometimes do not fully understand the risks they are undertaking at the time, further adding to the subsequent pain that can be potentially endured.
Risk Formula as applied to river rafting accidents
Risk Formula Applied to Triad River Tours’ Popular Commercial Rafting Activities (unofficial)
This is made using historical data, incident reports of American Whitewater, and the subjective opinions of staff/guides and other knowledgable/historical resources. Note that this is based on the events that have happened. Anyone can suffer a tragic accident or death on a river, but using a statistically significant analysis, we can gauge the severity based on what is most likely to occur.
Probability Metrics
Less than or near .01% (1 in 10,000). Rare
Less than or near .1% (1 in 1000). Unlikely
Less than or near 1% (1 in 100). Possible
Less than or near 10% (1 in 10). Probable
More than 10% = very likely or almost certain
Severity Metrics
No First Aid required (all is well)
Minor Injury requiring first aid
Injury requiring Doctor or Hospital visit
Major Injury
Fatality
Popular Commercial Whitewater River Sections of Western Washington
Sauk River (high water; above 4,000 cfs)
Probability: 3.5
Severity: 4
Risk Factor: 14
Sauk River (low water; below 2500 cfs)
Probability: 4
Severity: 2.5
Risk Factor: 10
Skykomish River (high water; above 5,000 cfs)
Probability: 4.5
Severity: 4
Risk Factor: 18
Skykomish River (low water; below 2500 cfs)
Probability: 4
Severity: 3
Risk Factor: 12
Skagit River (low water; below 8,000 cfs)
Probability: 2
Severity: 3
Risk Factor: 6
Skagit River (high water; above 8,000 cfs)
Probability: 3
Severity: 3
Risk Factor: 9
Snoqualmie River (low water; below 2400 cfs)
Probability: 4
Severity: 2.5
Risk Factor: 10
Snoqualmie River (high water; 2400-5000 cfs)
Probability: 3
Severity: 4
Risk Factor: 12
Combining Risk Formula with Generalized Whitewater RIsk Classification
Correlating the risk formula factor with classification
Controlling Risk Variables & Guest Accountability
It is important to recognize that the risk classification of a river is entirely separate from the ability of the participant to perform the tasks required for safe(r) passage, as well as the ability of the participant to sustain an injury or bad swim on a river trip. Further, the craft being utilized is also separate. A 13’ raft may be more likely to flip than a 15’ raft, but a 15’ raft may be slower to respond to a rescue; there are multiple variables to be accounted for. It is our best effort to provide you with this outline that showcases the primary variables that must be accounted for. Note that the river is the most objective aspect, and in fact, the participants are often the ones most likely to do something out of the ordinary.
River Conditions & Risk Assessment of River
High water risk increases flush drowning. Low water increases blunt trauma. Of the two, the higher water is the more significant risk to human life, so it is typically identified as higher risk, even though there are more incidents in lower water (see: Risk Formula above).
Participant Ability Level & Experience Level
Beginners increase likelihood of incident, as well as severity of incident due to lack of experience and familiarity with rescue procedures.
Participants who are not physically fit are less likely to be able to maintain the levels of exertion needed to paddle through big and long rapids, and therefore present an added risk.
Participants who cannot swim are not any less likely to end up in the river, but are more likely to be involved in a serious incident or fatality once in the river as they are not able to self rescue as easily as a person adept as swimming.
Equipment
Old worn out equipment can fail during a rescue, and must be replaced with new equipment.
Incorrect equipment being utilized, or a craft unfit for the conditions can increase the likelihood of an incident as well as hamper the response to the incident. In this case it is necessary to spend more money on diverse craft and equipment for varying conditions (especially in Washington where river levels constantly change).
Equipment that the guides are unfamiliar with does no good. Training must be included in every piece of equipment added to the safety system.
Staff
Beginner guides are more likely to be involved in incidents, and therefore are typically relegated to lesser risky river sections to build skill through diligent practice of safety maneuvers.
Entry level guides must be given the same training regarding hard skills as veteran guides, including but not limited to:
flip recovery drills
advanced first aid training
Swiftwater Rescue Training (SRT-1)
Veteran guides tend to be overconfident, and rely too much on their skills, therefore hubris is seen as a risk variable.
The “Dunning-Kruger Effect” is common among 2-4 year guides, who have a decent amount of experience, but may perceive their abilities being higher than they are.
