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Discover how freshwater moves across Earth's surface, from rivers to watersheds. Learn about erosion and the stages of river development.
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How does this freshwater flow across the surface of the earth?
RIVERS • Rivers? Streams? Creeks? They are all names for water flowing on the Earth's surface • Where does the water come from to fill these?
The Water Cycle • The continuous movement of water from the ocean to the atmosphere to the land and back to the ocean.
Continental divide of the United States • River systems are divided into regions called watersheds or drainage basins • This is the area of land that is drained by a water system. • River systems are separated from each other by areas of higher ground called a divide.
Definitions • Tributary: a stream that flows into a lake or into a larger stream • Channel: the path that a stream follows • Bed: the bottom of the stream • Load: the materials carried by the stream • Bed load: the materials carried along the bottom of the stream • Suspended load: materials carried in suspension (floating in the water) • Dissolved load: materials carried in solution, they usually cannot be seen.
How do these rivers form? • Erosion: the process by which soil and sediment are transported from one location to another. • It can be transported by wind, water, ice or gravity.
STREAM EROSION • As a stream forms it erodes soil and rock to make a channel. • When it first forms, it is usually narrow and steep. Over time, the stream transports more rock and soil downstream and makes the channel wider and deeper. • When streams become longer and wider they are called rivers.
Factors that influence a stream’s ability to erode • Gradient: measure of the change in elevation over a certain distance (how steep it is) • Discharge: amount of water that a stream or river carries in a given amount of time. • Load: the materials carried by the stream.
3 stages of a River • Youthful River • Mature River • Old River • Rejuvenated River
Characteristics of a Youthful River • Channel is eroded deeper rather than wider • Water flows quickly because it has a steep gradient • Has rapids and waterfalls • Have very few tributaries • HIGH erosive energy
Characteristics of a Mature River • Erodes channel wider rather than deeper • Does not have a steep gradient • Few rapids or waterfalls • Has many tributaries • Has more discharge than a youthful river • Has meanders
Meandering Stream • Mature rivers curve back and forth. The bends in the river are called meanders.
Characteristics of an Old River • Low gradient and low erosive energy • Instead of widening and deepening its banks, the river deposits its soils in and along its channel • Have wide flat flood plains (valleys) • Has few tributaries
Rejuvenated River • A river whose gradient (steepness) has been raised by tectonic activity (movement of the crust of the earth).
