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Water erosion - Coggle Diagram
Water erosion
Erosion
Erosion is a natural process by which rock and soil are broken loose from Earth’s surface at one location and moved to another.
Erosion changes land by wearing down mountains, filling in valleys, and making rivers appear and disappear.
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It benefits people by contributing to the formation of soil through the breaking up of rock. It causes rich soil to be deposited on valley floors and at the mouths of rivers.
One of the most harmful effects of erosion is that it robs farmland of productive topsoil. For this reason, it is one of the leading threats to the food supply.
Erosion can also wash valuable fertilizers from farmland and carry pollution–causing agricultural chemicals into lakes, rivers, and bays.
Eroded soil can clog irrigation ditches, ponds, and reservoirs. Gullies caused by flowing water may ruin fields by making them too small to farm with tractors and other modern equipment.
Factors affect streams
Velocity
A stream’s velocity, or the distance water flows during some period of time, such as feet per second, determines whether its flow will be slow or turbulent.
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The velocity of a stream or river determines the amount of sediment, or load, that the water can carry.
The change in elevation over a certain distance is a main factor in a stream’s velocity. A large elevation change gives a stream or river more erosive energy to erode rock and soil. A stream or river that has a small elevation change has less energy to erode.
In addition to eroding the land over which they move, rivers deposit, or drop, sediment when their velocity decreases. Deposits called bars can form when a river slows down as it travels around a bend in its channel.
Bars are made of sand and gravel are found on the river bend. As a river’s velocity increases, bars often move to an area of the river that flows more slowly.
Discharge
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The discharge of a stream increases when a major storm occurs or when warm weather rapidly melts snow.
As a stream’s discharge increases, its erosive energy and speed and the amount of materials that the stream can carry also increases.
Load
A river erodes a great deal of material from the land over which it flows. The materials carried by a stream are called the stream’s load.
In many rivers, most of the material is dissolved in the water and cannot be seen. This dissolved load, or sediment carried in solution, enters the water as it flows over rocks and soil.
In contrast with a dissolved load, a suspended load is sediment such as silt and clay that is in suspension. Most rivers and streams carry the bulk of their loads as suspended loads.
The finer particles may determine the color of the water, which may range from red to brown or yellow. The bed load of a stream or river is the sediment that is carried along the bottom of the channel.
The bed load includes larger sediments such as sand, gravel, pebbles, and boulders.
Stream development
Young streams
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Water flowing through a steep channel with a rough bottom has a high level of energy and erodes the stream bottom faster than its sides.
Mature streams
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Over time, most of the rocks in the stream bed that cause waterfalls and rapids are eroded by running water and the sediments it carries.
Erosion is no longer concentrated on the bottom in a mature stream. A mature stream starts to erode more along its sides, and curves develop.
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Water in a shallow area of a stream moves slower because it drags along the bottom. In the deeper part of the channel, the water flows faster. If the deep part of the channel is next to one side of the stream, water will erode that side and form a slight curve. Over time, the curve grows to become a broad arc called a meander.
The broad valley floor formed by a meandering stream is called a floodplain. When a stream floods, it often will cover part or all of a floodplain.
Old rivers
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In the upstream portion of a river system, you find whitewater streams moving swiftly down mountains and hills. At the bottom of the mountains and hills, you find streams that start to meander and are in the mature stage of development. These streams meet at the trunk of the drainage basin and form a major river.