Stream Erosion

A stream is a body of water that carries pebbles and particles down a channel. Streams are one of the main contributors to how the layout of the land changes over time. They do this by carving into the mountains over time by moving sediment and water through channels. This process can take thousands to millions of years. Streams can be in different phases depending on how old or young they are. In mountain areas streams carve them and create deep canyons. Streams go through phases of erosion and deposition of sediment. Stream erosion is something that takes up most of the streams energy from friction between the bed or sides and the water. A very young stream will be very windy and create very steep valleys by having an extremely fast velocity. For an older stream the landscape will be much flatter but will still have a sloping curve. The lack of mountains will decrease the velocity greatly. The stream will look like a braided channel form instead of steep valleys. The flood plains and sediment buildup cause this stream to change shape constantly. The last phase of a stream will be in an even flatter ground and will have slowed down the velocity even greater. The stream now meanders, or curves out in various places in a U shape.  

A stream is first created when multiple runoffs from precipitation run into each other to form one big stream. This runoff is carried across the land and picks up various sediments while doing so, it also gets this sediment from the breaking down of rocks and ground in its path. Streams carry this water from their source to the ocean or sea, which make them an important part of the water cycle and replenishing water. Most of the first cities were centered on streams for a constant source of water. This sediment can be carried far down a stream or it can be deposited and stored before reaching its final place. There are three types of load in a stream: solution, suspension, and bed load. Solution load, or dissolved load, is the portion of the load that is in the solution of the flowing water. It is all organic and inorganic material that is carried in solution.  Suspended load is the portion of the stream that is permanently suspended in flowing water. Suspended load includes many different silts and clays. They remain suspended by turbulent flow. The final load is bed load, which is when pebbles and sand move along the flow of the stream without being permanently suspended in the water. These materials are too heavy and move along the bottom of the stream by rolling or sliding, which erode the channel by abrasion. Another way they move is by saltation, a jumping movement, which happens when particles suspended in the stream fall to the bed and dislodge other particles which repeat the process. These three different types of loads help to erode the surrounding rock and stream bed which adds to more sediment.

http://www.physicalgeography.net/fundamentals/10y.html

http://www.earthonlinemedia.com/ebooks/tpe_3e/fluvial_systems/geologic_work_of_streams.html

http://www.tulane.edu/~sanelson/eens1110/streams.htm