Re: [Paddlewise] ACA Accident Report - Critical Judgement II

On Sun, Jan 20, 2008 at 07:42:58PM -0800, Bradford R. Crain wrote:
>   According to the ACA Report, Table 13 below, roughly equal
> numbers of novice paddler and experienced paddler fatalities
> were tabulated in this study, giving the false impression
> that novice and experienced paddlers are dying at the same
> rate. The counts have not been adjusted for total hours of
> risk exposure per paddler, nor has the data been adjusted
> for degree of severity of environment in which each paddler
> has been operating. Clearly this data should be adjusted for
> total risk exposure, just as a cancer patient would be. I find
> this table terribly misleading.

This is a superb point.  And I'd include in that "severity of
environment" factors such as:

	- whitewater class
	- whitewater type (continuous vs. pool-and-drop)
	- weather conditions
	- remoteness
	- river levels as compared to "normal"
	- etc.

Various attempts at quantifying factors like those have been made over
the years.  A notable example may be found in Monte Smith's "Southeastern
Whitewater" where he explains his "TRIP" scale and uses it to assess
several dozen well-known runs throughout the southeast US.  Of course
his scheme, like any other, is largely empirical -- but based on my
own first-hand experience on a number of those runs, it's at least
in the ballpark.  Most of its utility lies not in the absolute values
of the numbers -- which are, after all, arbitrary -- but in the *differences*
of those values for different runs.  Those differences enable paddlers
familiar with run A but not run B to reach conclusions such as "run B
is about as hard as run A" or "B is markedly more difficult than A"
with reasonably high confidence that those conclusions are accurate.

	[ Briefly, here's how the TRIP scale works.  Nine numbers
	that assess stream difficulty are (in some cases) measured
	or (in some cases) assigned.  Those numbers are then weighted
	and combined to produce a single TRIP number.  The nine
	factors and their weights are:

	23%	difficulty of rapids
	20%	volume X gradient interaction
	17% 	average gradient
	10%	streambed morphology
	7%	continuousness of rapids
	7%	maximum gradient in any one mile
	6%	total gradient
	6%	inaccessbility
	4%	reputation

	Some folks have wondered why that last one is in there --
	I think it's reasonable.  Paddler psychology *is* a factor:
	even though there are sections of the Upper Meadow that
	are arguably more difficult (especially above 1000 CFS)
	than sections of the Lower Gauley, paddlers on the latter
	have in their heads "I'm on the $#*&! Gauley" and that
	does make a difference.

	Note that he doesn't factor in river level or weather:
	his assessments are made at nomimal water levels (which he
	specifies) and he does include comments about how his
	assessments change under high-water conditions.  And I think
	anyone using his book is likely well aware that paddling
	the New River Gorge on a sunny July day is a profoundly
	different experience than running it in a March snowstorm
	even if water levels are identical. ]

I'm not claiming that Smith's methodology is the best; I just think
it's a credible attempt.  And something roughly along those same lines
needs to factored in to studies like this in order to (as Brad said)
adjust it for total risk exposure.

And I'd also add this factor: familiarity.  I've paddled one local
stream several thousand times (I trained there nearly every day for years)
under every possible condition, including record low and record high.
It's probably "safer" for me than some easier streams, because I know
every rock, every wave, every eddy and exactly what they'll do under
any condition.  The same can probably be said of people who run the
Ocoee or the Clackamas or any other stream all the time.  Whereas if
any of us were on the others' "home river" for the first or second
or Nth time, we'd probably incur higher risk.

---Rsk
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