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Name: Jack
Status: Student
Grade: 9-12
Location: London
Country: United Kingdom
Date: July 2006


Question:
Is there a pattern for the way rivers meander as they flow or a reason why they do not run in a straight line down? Can this meandering be predicted? How can the meandering change over time?



Replies:
Jack,

As you probably already know, a meander is caused by the combination of erosion and sediment deposit. As a river flows, it carries sediment with it. A slight change in the speed of water flow between the two banks (this can be caused by anything from a tree fall, a rock, etc) can cause the beginnings of a meander. At the slower side of the river, more sediment gets deposited because the river will have less kinetic energy and can not continue to carry to carry as much sediment. On the faster side of the river, less sediment gets deposited and more erosion of the river bank takes place (precisely because the water is flowing faster).

This effect gets multiplied because as the bend develops the slower side of the river will continue to get slower (there is less distance for the water to travel) and the faster side gets faster. Thus more sediment gets deposited on the slow side and more erosion happens on the fast side. The bend gets more and more pronounced.

Sometimes the river may cut through bend forming an oxbow or a loop (if the flow is less resisted at the shorter distance).

River flows can be modelled and somewhat predicted. For example, in general younger rivers tend to flow fast, have fewer tributaries and tend to erode from the river bed. More mature rivers tend to flow slower, have more tributaries and tend to erode its banks instead of the river bed. Old rivers tend to be associated with flood plains. Rivers that flow through mountains do not meander as much (the mountains resist bend formation) and form braided patterns instead.

Greg (Roberto Gregorius)



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