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Explore the source of rivers, erosion processes, and the water cycle. Learn about river systems, tributaries, watersheds, channels, gradients, discharge, load, and types of rivers.
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11.1 The Active River
Do you think a river can have a source? Describe where you would expect to find a river’s source. The source of a river is where it begins. It is often a place where runoff collects or where a spring surfaces. There river source is usually on high ground.
Erosion • The process by which wind, water, ice, and gravity move soil and sediment from one place to another. Beach Erosion Gully Erosion
What is erosion, and how does it shape Earth’s landscape? Erosion is the process by which wind, water, ice, and gravity move soil and sediment from one place to another. This process shapes Earth’s landscape.
Water Cycle • The continuous movement of water between the atmosphere, the land, and the oceans.
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Describe the water cycle. The water cycle is the continuous movement of water between the atmosphere, the land, and the oceans.
River System • A network of streams and rivers that drain an area of its runoff.
Tributary • A stream that flows into a lake or into a larger stream.
Describe the difference between a tributary and a river system A tributary is a stream that flows into a lake or larger stream. A river system is the entire network of streams and rivers that drain an area.
Watershed • The area of land that is drained by a river system.
River • A main stream that drains a large watershed and has many tributaries.
Divide • An area of higher ground that separate the watersheds.
Channel • The path that a stream follows.
Gradient • The measure of the change in elevation over a certain distance.
How does gradient affect the erosion of stream channels? The higher the gradient of a stream, the more erosive energy stream has.
Discharge • The amount of water that a stream or river carries in a given amount of time. • Increases with storms.
Load • The materials carried by a stream. • Fast-moving streams carry large particles and high rate of erosion.
How does load affect rates of erosion? The larger the particles in a stream’s load, the higher the rate of erosion is.
Youthful Rivers • Erodes its channel deeper rather than wider. • Channel is narrow and straight. • Very few tributaries. • Rivers flow quickly because it is steep.
Mature River • Erodes its channel wider. • Gradient is not steep. • Fewer falls and rapids. • Many tributaries. • Large watershed therefore more discharge.
Describe the difference between youthful rivers and mature rivers in terms of how these rivers erode their channels. Mature rivers erode their channels wider rather than deeper. Youthful rivers erode their channels deeper rather than wider.
Meanders • The curves or bends in the river’s channel.
Rejuvenated Rivers • Forms where the land has been raised by tectonic activity. • Gradient is steeper. • Flows quickly. • Cuts deeply into valley floor.
Terraces • Step like formations that form on both sides of a stream valley because of rejuvenation.
Old Rivers • Low gradient. • Little erosive energy. • Has wide, flat floodplains, or river valleys, and many bends. • Fewer and smaller tributaries.
Oxbow lake • Forms when the strip of land that separates parts of a meander is eroded.
Review Questions • What are three factors that affect the rate of stream erosion? * Gradient, discharge, and load affect the rate of stream erosion. 2. How are river systems part of the water cycle? * Rivers transport water that falls as precipitation and runs off the land. This water may evaporate into the atmosphere where it may condense and fall again as precipitation.
How do youthful rivers, mature rivers, and old rivers differ? • *Youthful rivers erode deep channels. Mature rivers erode wide channels. Old rivers deposit sediment in their channels along their banks.
Explain how a river system is part of the water cycle. Then, describe how the Earth’s water cycle and river systems may be affected if the sun’s rays are significantly blocked by pollutants in the atmosphere. • * Rivers are part of the water cycle in that they transport the water that falls from the atmosphere as precipitation. The water in the river may then evaporate into the atmosphere. If pollutants blocked out some of the sun’s energy, evaporative would decrease. With less precipitation, rivers would lose some of their discharge and, erosive power.
