Title: Rivers Brown 24-25
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# Rivers Moving current of freshwater flowing downslope
Most powerful shaper of earths surface
Source of freshwater for irrigation & drinking, transportation, recreation, hydropower, waste removal
What is a River? Distribution of Earths Water What is a River System?
A river system includes the trunk stream and all of its tributaries
A tributary is a smaller river that flows into a larger river Parts of a River System
1. Headwaters 2. Trunk Stream 3. Mouth
Water in a river system flows downslope from the head toward the
mouth , fed by runoff and groundwater from the entire watershed.
> Weathering & Erosion
> Deposition
> Transportation
> Melting snow & ice, springs (groundwater)
Watersheds/Drainage Basins
The borders of a watershed are higher elevation ridges that help define the drainage direction, they are called divides. Water that falls on the land within the watershed eventually drains out through the mouth of that river. When is it runoff and when is it a river?
a) Runoff flows over land without a channel
b) erosion starts to take away sediment and form a
channel - the beginnings of a river! c) erosion lengthens the channel backwards up the slope HEADWARD EROSION
Channels created by erosion What 3 Rivers run through Concord?
> 1. Concord 2. Sudbury 3. Assabet
## Our Local River Systems and Watersheds
The Charles, Neponset, and Mystic river
Merrimack River Watershed (Pemigewasset River to to Newburyport) Egg Rock
Confluence of the Assabet & Sudbury The Mississippi River Drainage Basin
Largest Drainage Basin and River System in the United States
> The Great Divide!
## The Triple Divide Peak Erosion vs. Deposition
The shape and features of a river system form through a combination of Erosion and Deposition Which one is taking place depends on velocity and Gradient
> Erosion is taking sediment away
Deposition is putting sediment down The Importance of Gradient: Erosion vs. Deposition
Gradient means steepness of slope Steeper gradient means more erosion, steeper near head Gentler gradient means more deposition, flatter near mouth Sediment that has been eroded by running water...
Will be transported along the bottom or in the current. The bigger sediment at the bottom helps the river further erode its channel, acting through abrasion. As the rivers gradient or velocity decreases, sediment load is deposited.
This is why some rivers appear muddy
Remember: Running water erodes sediment by: 1. Lifting 2. Abrasion 3. Dissolving 4. Saltation Erosion by dissolving: How rivers make the ocean salty Characteristics of a River by Age or Stage
Rivers develop based on the gradient of the slope
>
But the gradient will change over time as the river erodes sediment!
Therefore a river will develop over time (it will age)
Age is based on the features and characteristics of a river , not its age in years
Gradient determines the age of river The 3 Ages/Stages of a River
1. Young Steep gradient 2. Middle Medium gradient 3. Old Gentle gradient Flowing over steep, rocky surfaces
Steep gradient and high velocity means great erosive power but not much deposition
narrow, fairly straight, V-shaped valleys
Lots of tributaries, white water rapids, waterfalls
Young Rivers Young River Features
V-shaped valleys
Whitewater Rapids
Waterfalls
# VWhite Water Rafting! Middle Rivers
Lower gradient -medium/intermediate
Wider valleys
rivers begin to erode
side-to-side, not just down.
Both erosion and deposition occur in this environment
Meanders develop - rivers flowing over gently sloping ground that begin to curve back and forth across the landscape Rivers in sediment, on low gradient, like to meander
Meanders grow and migrate, developing a wider, flat
floodplain over time Side-by-side erosion and deposition
Faster velocity on outside of the meander curve causes erosion (CUTBANK ) and widening of meander curve
Slower velocity on the inside of the meander curve means the current deposits sediment (POINT BAR )
Velocity matters!! Old Age Rivers
Very low gradient as river reaches sea-level or other base-level
Wide valleys with broad meanders and floodplains
Frequent floods deposit natural levees
Backswamps, yazoo tributaries, oxbow lakes, meander scars
Depositional delta develops at river mouth with distributaries The evolution of an oxbow What evidence is there that the river channel has migrated? The many courses of a single river Major Rivers, Major Deltas
As a river hits sea level, the velocity decreases and sediment is deposited Results in a fan shaped growth of land called a Delta River Delta Formation How "levee wars" are making floods worse All the water, all the sediment Water and sediment is not the only thing rivers bring to the ocean... In U.S., it is getting better but there is a long way to go
50 years ago the Cuyahoga River in Ohio was so polluted by industrial waste it would frequently catch fire. Today there is a national park. Rivers and Us. Rivers have found their way into our lives both by a physical and metaphorical connection. Lets examine the relationship between rivers and humans. Think about that relationship environmentally, economically, and culturally. Here are some quotes to get you thinking about rivers.
And the Mississippi's mighty But it starts in Minnesota At a place that you could walk across With five steps down And I guess that's how you started Like a pinprick to my heart But at this point you rush right through me -GHOST by Indigo Girls
No man ever steps in the same river twice, for its not the same river and hes not the same man.
- Heraclitus (Greek Philosopher)
Rivers never flow in reverse, so try to forget your past, and focus on your future - Anonymous
"We have become great because of the lavish use of our resources. But the time has come to inquire seriously what will happen when ...the soils have still further impoverished and washed into the streams, polluting the rivers, denuding the fields and obstructing navigation." - Teddy Roosevelt