Page 14
The INDEPENDENT, January 6, 2011
Resident shares knowledge of Do-It-Yourself flood forecasting
by William Langmaid
If you’ve lived in Vernonia for
any time at all, chances are you
know someone who was affect-
ed by a flood. We had one in
1996, and then another in
2007. Other events have oc-
curred as well, but they were
much more localized than ei-
ther of those 100-500 year
flood events. As winter ap-
proaches, people look fearfully
at the rivers, certain that the
floods will happen again.
Well, that’s true, they will,
but it takes a very specific set of
circumstances for a flood to oc-
cur. It’s not just when we get a
lot of rain, or just when there is
snow on the ground, or when
the folks on the Portland news
stations are casting about for
another sensational story and
want to speculate on a recur-
rence of high water.
Now, I am no expert in any of
the fields which are typically as-
sociated with flood forecasting,
but I did pay attention to the
available data and made some
key observations of the data’s
behavior during the flood
events. Hopefully you’ll gain
some knowledge from this arti-
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sure to be prepared by follow-
ing official recommendations as
they are issued.
The two key floods in our re-
cent history were similar in
components, even if they acted
differently. In 1996 the flood hit
in the middle of winter, when
we had had very cold weather
followed by snow. This did two
things. It made the ground im-
permeable, like a parking lot,
and the snow provided water
storage. The amount of water
in one cubic foot of powdery
snow is considerably less than
that in one cubic foot of slushy
snow.
In 1996 it didn’t. The Pineap-
ple Express headed right up
the Willamette Valley, and the
combination of very warm
weather and heavy rains over a
few days melted all that slushy
snow. But the ground stayed
frozen, and the melted snow
and rain just ran to the valley
bottoms and into the rivers. So,
1996 was frozen ground, a de-
cent snowpack, lots of rain, and
warm air.
The 2007 flood was caused
by hurricane-like conditions.
There was a super-saturated
weather system that moved
quickly to the coast and then
stalled as it climbed the Oregon
coast range. As it stalled, the
western edge of the system
was still over the ocean, picking
up water, which it then dumped
over the land. A total of 11” fell
in the Vernonia area, at a pro-
longed rate of .4” per hour.
The rain alone would have
caused some flooding, but the
real kicker was that the rain
was being absorbed into the
upland snow. The hurricane
also brought warm air, and that
warm air increased the temper-
ature from 32 to 50°F in 24
hours, and melted all the snow,
releasing 9” of rain in fewer
than 8 hours. That meant there
was an effective rainfall rate of
over 1.5” every hour.
The river rose at a rate of 7”
per hour on the Clear Creek
gauge, and when those waters
ran into the flow from Rock
Creek, it was too much. Both
rivers slowed down and backed
up, dumping water over their
banks and into the town. The
events leading up to the flood-
ing were eerily similar, and al-
low us to predict our future ac-
tions with some accuracy.
Rapidly increasing tempera-
tures, saturated snowpack, and
heavy rains were shared char-
acteristics. The main difference
was that the 1996 rain event
lasted several days, and the
2007 event lasted one day.
That is what happened, and
here are some tools to help you
monitor the river. By looking at
the USGS website (http://wa-
terdata.usgs.gov/nwis/uv?1429
9800) that shows the Clear
Creek gauge, anyone can
check the rate of increase in
the river height. Since the river
is a modified vee shape, mean-
ing the bankful width is greater
than the bed’s width, it takes
more volume of water to in-
crease height as it gets higher.
For example, at 5’ of depth, the
river is moving 270 cubic feet
per second (cfs). At 10’, still un-
der flood stage, it has in-
creased twelvefold, to 3,270
cfs. It more than doubles again
to reach 15’ (it peaked at 18.6’
in 2007) flowing at 8,640 cfs.
When I am monitoring the
river because of my interest in
evacuating the food bank, I am
only interested in height in-
creasing after it hits 9 feet. This
is an important number be-
cause there is already a signifi-
cant, but not dangerous, vol-
ume of water at that level. I
then look at the shape of in-
crease, and if it looks like a very
steep line, with an increase of
over .4 feet per hour, then it is
important for me to look at oth-
er indicators, like snowpack,
temperature, and duration of
rain forecast.
The Snotel-Saddle Mountain
recording station is also avail-
able on the web, but isn’t as
user friendly. The site is located
at http://www.wcc.nrcs.usda.
gov/nwcc/site?sitenum=726&st
ate=or but the data is obscured
by some links. The easiest one
to use to get the information is
the Snow Water Equivalent
hourly chart for the last 7 days,
selected by the relevent report
features and clicking on the yel-
low [View Current] button.
Since this area accumulates
snow all winter, the important
indicators here are temperature
increasing and snow pack de-
creasing. Those two, com-
bined, mean additional water,
beyond rainfall, will be entering
the rivers.
The final site I watch is the
north coast National Weather
Service (NWS) forecast report
at http://forecast.weather.gov/
MapClick.php?zoneid=ORZ00
3. This is a forecast for a pretty
general area, but the important
factors are when they warn
about unusual amounts of rain,
and rapidly warming tempera-
tures.
The floods of ‘96 and ‘07
were learning experiences for
the NWS, and now they broad-
cast those warnings in conjunc-
tion with any flood warnings.
Keeping these sites book-
marked in your browser can be
helpful. There are more re-
sources out there, but these
are what I use.
Healthy habits
can help you
live longer
From page 11
enjoy life more. People with
positive attitudes decrease
their risk of poor health and
early death by 50% over pes-
simists.
• Establish healthy habits.
Get regular physical checkups,
blood pressure and cholesterol
checks, floss daily, don’t
smoke, and drink in modera-
tion. Move around and get reg-
ular exercise every day. Slow
down your fast life pace – take
time to relax.
• Watch your waist and exer-
cise regularly. It is hard to find
obese centenarians. Keeping a
trim waistline is one of the keys
to living longer because ex-
cess weight contributes to
heart disease, high blood pres-
sure and diabetes. Be smart
about what and how much you
eat. Eat more fruits and veg-
gies, less red meat and fries.
• Faith matters. Older peo-
ple with an active faith had low-
er blood pressure and lived
longer, according to a study at
the Duke University Medical
Center. Churches or religious
services provide a social net-
work and a source of comfort
and support.
• Be a volunteer. When vol-
unteering, you are making
friends, helping people, having
a social connection and experi-
encing the psychological bene-
fits of feeling needed. People
who spend time volunteering in
the community are happier and
healthier.
Source: Nina Chen, Ph.D., CFLE,
University of Missouri Extension