All rivers meander, but why do they meander and what causes them to meander? How does this meandering cause a river to form an ox bow lake? This has been a topic which many scientists have studied and attempted to come up with a logical explanation of why. The explanations range from very simple to extremely complex. The concepts behind a meandering river are actually very simple and a great example of how physics can be applied and seen in the natural world around us.
The first thing which should be explained is what exactly a meander is. A meander is a bend in a river. All rivers meander at some point, this is caused by a river trying to follow the greatest gradient to flow down and the easiest path to cut through. An example would be if a river hits a large rock formation it would rather go around the formation than cut through it if possible. This helps to explain one of the reasons rivers change direction over time, the slightest change in direction can drastically change the flow of a river. The most easily visible meanders are seen in open areas with flat terrain where there is more loosely packed soil and few to no rock formations or other obstacles. A river which has many large meanders is often described as if you were looking down at a slithering snake.
A meander is formed and changes over time because of the many forces at work. The first thing to look at is the velocity of the water. The water towards the outside of a meander is moving at a faster speed than the water towards the inside of the meander. This is caused when water enters a bend and is thrown to the outside of the bend (similar to the feeling of when you are riding in a car and go around a bend). The water towards the inside of the bend has a much slower flow because it is not being thrown outwards. When you look at the river bed you can see how the river changes over time due to the different forces of the water. The inside of a meander will have a more gradual slope as compared to the outside of the meander which is a steep more abrupt slope. The river is usually deepest closer to the outside of the meander. Because the water on the outside of the meander is flowing at a faster rate it causes erosion. The erosions is caused when the water pushes up against the outer bank, because the outer bank pushes back it causes friction. The friction causes some sediments from the outside of a meander to be carried away with the water. Because the water on the inside of a meander is slower it causes deposition, the water does not have enough force to carry any sediments from the inside of a meander away so instead it will deposit the sediments from the outside of the meander. When these two things occur in combination they change the river over time by causing it to move outwards in the direction of the outer bank.
To better understand how the deposition and erosion work you have to look at the actual flow of the river. When a river enters a bend it has secondary flow which moves in a circular motion. If you were to look at a cross section of a river you would see something which looked like the water was being stirred. This secondary flow carries the sediments from the outside of the bend towards the inside where they are deposited.
The erosion and deposition are what cause an ox bow to form. This happens when the outer bends of two meanders erode away and overtime will eventually become connected. This causes the river to flow in straighter path, over time as the flow changes and eventually the bend will be cut off from the river and form what is called an ox bow lake. Overtime ox bow lakes will dry up and all leave a scar. This also shows how a slight change in the flow of a river in one area can significantly change the flow of the river.
Aslamazov, L. G., A. A. Varlamov, and A. A. Abrikosov. "Chapter 1: Meandering Down to Sea." The wonders of physics. Singapore: World Scientific, 2001. 4-11. Print.
"Meandering Rivers." SCPRO: Sierra Club Potomac Region Outings Program. N.p., n.d. Web. 14 Oct. 2011.
"The Meandering River." Our Watershed Atlas, Bryant Creek, North Fork, Eleven Point, Spring River, Missouri Ozarks. N.p., n.d. Web. 14 Oct. 2011.
Walker, Jearl. "Chapter 2 Fluids." The Flying Circus of Physics. 2nd ed. United States of America: Courier/Westford, 2006. 93-94. Print.