Except for the Big Thompson fly fishermen and tubers lolling down
Boulder Creek, most residents of the Colorado Front Range usually pay
little mind to the small rivers that trickle by on their way from the
mountains to the plains.
Until this week, when more than a foot of rain from a storm system hung
up on the Rocky Mountains supercharged those streams and others with a
deadly force that left vast corridors of destruction stretching from the
foothills to the farmland of the plains.
"The water came over and it was 2, 3 feet deep and broke our doors
down," said Jack Hammond, who left his home in the foothills west of
Lyons for a Fort Collins shelter with his wife, their daughter and their
dog.
Dams along a chain of five small reservoirs failed upstream of Hammond's
home on a Little Thompson tributary as the rain picked up Wednesday. As
the family huddled upstairs, water downstairs toppled their
refrigerator and dumped 6 inches of mud. Finally, on Friday, a Colorado
National Guard helicopter hoisted them and their young German shepherd
to safety.
In semi-arid Colorado, the problem is usually too little rain that leads
to drought and wildfires. But when the skies open up, the potential for
the biggest drenching lies along the Front Range, where the eastern
foothills meet the plains and most of the state's population lives.
Under the right circumstances, a moist air mass can hit the foothills
and get stuck. Moisture turns into rain — in the winter, snow — and just
keeps falling. That's what happened last week, when a storm system
parked itself over a big swath of the state with so much embedded vapor
that forecasters described it as tropical.
Colorado is far from tropical moisture sources, meaning those factors
come together rarely, perhaps once every 10 to 15 years, said Nolan
Doesken, the state climatologist at Colorado State University.
It's difficult to predict monster storms, meteorologists say, and early
computer models forecast 3 inches of precipitation would fall from the
statewide system. That amount alone would be "a big deal" for dry
Colorado — a big fraction of its annual rainfall, Doesken said.
"That far in advance, you couldn't say it was going to be Boulder Creek,
St. Vrain, Poudre," he said, naming several flooded waterways. "You
just knew there would be ingredients in place for substantial
precipitation for the parts of the state that would be vulnerable."
But then all that moisture bumped against a sprawling, counter-clockwise
wind pattern that pushed it repeatedly up the slopes of the foothills.
It condensed, fell as rain, and then the cycle repeated.
In Boulder alone, the system dropped a record 9 inches between Wednesday
and Thursday evenings, smashing the old record of 4.3 inches. By week's
end, Boulder County had as much as 15 inches in some areas.
When the rains come, the mountain topography can turn it into disaster.
All that water is channeled into a handful of narrow, steep canyons that
concentrate the rushing runoff, giving it the strength to push cars,
boulders and even buildings out of the way.
It's happened before several times in the state's history, including a
1965 flood in Denver that killed between 20 and 30 people. In 1976, the
state's deadliest flood killed 144 people in one of the areas devastated
by the latest flooding, Big Thompson Canyon.
.jpg)
0 comments:
Post a Comment