WEBVTT

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[rushing water] 

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What is a flood? A flood is just too much water

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 in the wrong place. The bigger question is why?

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Why does too much water end up in the wrong place?

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The factors that determine whether

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or not a place will flood are the same

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no matter where you are. Knowing 

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the components of a flood can also help predict how often and

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how big or damaging those floods will be when they do occur.

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[music]

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[music]

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The Carbon River area in the northwest corner 

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of Mount Rainier National Park is notoriously prone

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to flooding. A flood occurs when there is too much water flowing in a 

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particular place. So what is it about the Carbon River that causes it 

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to flood so frequently? Different places can handle

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different amounts of water and the Carbon River area deals with a lot. 

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On average, the area gets over 

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80 inches of precipitation a year. When moisture-laden air 

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from the Pacific ocean collides with the massive slopes of Mount Rainier

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the result is lots of rain, or at higher elevations,

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snow.

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[music]

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As a result of the frequent rain, the 

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Carbon River area is home to a dense temperate rain forest.

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Old growth trees, mosses, ferns, and numerous other plants

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thrive on the high amounts of rainfall. Some of the

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moisture falls as snow and becomes trapped as part of the Carbon Glacier.

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Excess water collects in numerous 

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creeks and streams in the area

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all eventually flowing into the powerful Carbon River.

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Even under normal conditions, 

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the Carbon River can handle a lot of water. However, even

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places with a large capacity for water like the Carbon River area have

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a limit. During the November 2006 flood, the largest flood

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in the park's recorded history, it rained 18 inches in 

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three days. The Carbon River area normally handles only 17 inches

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of rain in the entire month of November.

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[music]

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Many factors affect whether or not a place

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like Carbon River can adapt to extreme amounts

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of rainfall like what fell during November of 2006.

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The Carbon River is a large river 

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capable of transporting a lot of water.

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Lush forests divert some rainfall, while 

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glaciers store even more water as ice. However frequent rain

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can also saturate soils and water log even the densest forest.

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Changing climate is affecting weather patterns, creating 

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larger storms with more intense rainfall than in the past. 

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[music] 

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A process called aggradation

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is also restricting the ability of the Carbon River to carry water.

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Aggradation is the opposite of erosion. 

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Mount Rainier's glaciers create so much rocky material and sediment as 

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they grind down the mountain

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that the rivers can't move it all. 

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Plus, as climate change melts

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glaciers faster than ever, even more rocky material enters the river.

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When the river channels fill up, 

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the river is forced in new directions

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creating braiding of the river channels. Even under

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normal circumstances aggradation can cause 

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rivers to dramatically alter course. 

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During flood events, the process of aggradation is 

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accelerated, amplifying the effects of too much water in the system.

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[music] 

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Often rivers end up flowing through surrounding forests

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 as well as any human construction in the way.

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Floods are a natural and often 

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necessary part of a healthy environment. Sediments deposited by

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flood waters provide much needed nutrients for new vegetation.

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The powerful force of the water 

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scours river beds of debris and creates new habitat

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for fish and aquatic insects. Floods are also

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very damaging, particularly to human roads and structures.

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Unfortunately the Carbon River Road was built along the edge

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of the Carbon River. 

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When aggradation fills up the river channels

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the easiest path for the water is often the road itself. This conflict

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with human use has played out repeatedly throughout the roads history.

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[music]

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As long as the conditions that cause flooding persist, 

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then floods will continue to happen in the Carbon River area. 

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Glaciers are shrinking due to climate change, 

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releasing more water and rocky material 

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into the river system. The process of aggradation

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is accelerating. Rain will continue to fall. 

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Human use however is within our control. By better 

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understanding the anatomy of floods, 

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Mount Rainier National Park plans for the future 

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so that a balance can be struck that allows for the 

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natural processes of the river as well as for human use.

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[music]

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