[rushing water]
What is a flood? A flood is just too much water
in the wrong place. The bigger question is why?
Why does too much water end up in the wrong place?
The factors that determine whether
or not a place will flood are the same
no matter where you are. Knowing
the components of a flood can also help predict how often and
how big or damaging those floods will be when they do occur.
[music]
The Carbon River area in the northwest corner
of Mount Rainier National Park is notoriously prone
to flooding. A flood occurs when there is too much water flowing in a
particular place. So what is it about the Carbon River that causes it
to flood so frequently? Different places can handle
different amounts of water and the Carbon River area deals with a lot.
On average, the area gets over
80 inches of precipitation a year. When moisture-laden air
from the Pacific ocean collides with the massive slopes of Mount Rainier
the result is lots of rain, or at higher elevations,
snow.
[music]
As a result of the frequent rain, the
Carbon River area is home to a dense temperate rain forest.
Old growth trees, mosses, ferns, and numerous other plants
thrive on the high amounts of rainfall. Some of the
moisture falls as snow and becomes trapped as part of the Carbon Glacier.
Excess water collects in numerous
creeks and streams in the area
all eventually flowing into the powerful Carbon River.
Even under normal conditions,
the Carbon River can handle a lot of water. However, even
places with a large capacity for water like the Carbon River area have
a limit. During the November 2006 flood, the largest flood
in the park's recorded history, it rained 18 inches in
three days. The Carbon River area normally handles only 17 inches
of rain in the entire month of November.
[music]
Many factors affect whether or not a place
like Carbon River can adapt to extreme amounts
of rainfall like what fell during November of 2006.
The Carbon River is a large river
capable of transporting a lot of water.
Lush forests divert some rainfall, while
glaciers store even more water as ice. However frequent rain
can also saturate soils and water log even the densest forest.
Changing climate is affecting weather patterns, creating
larger storms with more intense rainfall than in the past.
[music]
A process called aggradation
is also restricting the ability of the Carbon River to carry water.
Aggradation is the opposite of erosion.
Mount Rainier's glaciers create so much rocky material and sediment as
they grind down the mountain
that the rivers can't move it all.
Plus, as climate change melts
glaciers faster than ever, even more rocky material enters the river.
When the river channels fill up,
the river is forced in new directions
creating braiding of the river channels. Even under
normal circumstances aggradation can cause
rivers to dramatically alter course.
During flood events, the process of aggradation is
accelerated, amplifying the effects of too much water in the system.
[music]
Often rivers end up flowing through surrounding forests
as well as any human construction in the way.
Floods are a natural and often
necessary part of a healthy environment. Sediments deposited by
flood waters provide much needed nutrients for new vegetation.
The powerful force of the water
scours river beds of debris and creates new habitat
for fish and aquatic insects. Floods are also
very damaging, particularly to human roads and structures.
Unfortunately the Carbon River Road was built along the edge
of the Carbon River.
When aggradation fills up the river channels
the easiest path for the water is often the road itself. This conflict
with human use has played out repeatedly throughout the roads history.
[music]
As long as the conditions that cause flooding persist,
then floods will continue to happen in the Carbon River area.
Glaciers are shrinking due to climate change,
releasing more water and rocky material
into the river system. The process of aggradation
is accelerating. Rain will continue to fall.
Human use however is within our control. By better
understanding the anatomy of floods,
Mount Rainier National Park plans for the future
so that a balance can be struck that allows for the
natural processes of the river as well as for human use.
[music]