From: "Timpe, Jim" <Jim.Timpe@xxxxxxxxx>
I'd like to know who propagated the myth that it doesn't snow in western
Oregon.
Last I checked, Jim, Fluke is in Everett, Washington -- about 200-400
miles further north than Oregon covered bridge country, and more
subject to cold, so I could understand your not being familiar with
Willamette Valley weather!
Where I live (a Portland suburb, at the North end of the Willamette
Valley), we get snow that stays for more than a day perhaps every
third year. In the 16 years I've been here, there's never been more
that four or five inches, although there have been a couple good ice
storms. And this is the colder, northern end of the valley,
influenced by continental highs that pump cold air through the
Columbia Gorge. In the mid-valley, where most of the bridges are,
there is even less snow.
Sure, there's the argument that 100 years ago, when these bridges
were built, the climate was a bit colder.
The covered bridges in the Willamette
Valley are covered for precisely the same reason that they're covered in the
northeastern US.
Which is to keep them from rotting out, not to keep them from falling
down from the weight of snow.
But don't take my word for it, get a pencil and a napkin! Many such
bridges have a 10 ton limit. Let's call it 10 metric tons, and skip
the napkin and do the math in our heads. (Flame bait: when is America
going to stop being so stupid about units of measure?)
That's 10 million grams, or 10 million cubic centimeters of water.
The weight density of snow varies all over the place, but let's call
it 1/10th that of water to keep the numbers round -- 100 million
cubic centimeters of snow, or 1,000 cubic meters.
Again, to keep the numbers round, let's say the bridge is 6 meters
wide and 16 meters long -- an exceptionally wide bridge (and a bit
long, too) by covered bridge standards, but having a convenient area
of 100 square meters.
So a big nor'easter blows in and dumps 10 meters of snow on the
bridge, and it fails! This has gotta happen, what, every ice age or
so? Heck, let's even assume that it's especially dense snow -- as
dense as water, in fact -- and get rid of our factor-of-ten fudge for
snow. You'd still have to flood that bridge with an entire meter of
water for it to fail!
I might have slipped a decimal here or there, but I'd also be
surprised if the bridge weight limit didn't have a hefty contingency
factor. I also tried to err conservatively in the other assumptions.
And true, they're now maintained for tourism reasons more
than anything else.
Still an un-proven assumption -- shall we get out another napkin, and
this time talk tax base and maintenance costs? :-)
Any decent bridge can cost seven figures these days -- even at
municipal bond rates (about 5 0.000000e+00re in Oregon), that justifies
perhaps $50,000 of annual maintenance. Just how much does it cost the
highway department to put a coat of paint on every few years, and new
shingles every 20 or so? The above-mentioned hypothetical bridge
could be re-roofed for $3,300 -- it's coincidentally about the size
of the house I just had roofed!
Then there's the flip-side of the equation -- do you imagine each
bridge brings in $50,000 in tourist dollars each year? That might
take a bit more research than a napkin and pocket calculator to prove
to me.
I'm sticking with "cheaper to maintain than replace" over tourism,
but hey -- I'm willing to listen to arguments at least as thought out
as my own... :-)
--
: Jan Steinman <mailto:Jan@xxxxxxxxxxxxxx>
: Bytesmiths <http://www.bytesmiths.com>
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