Types of Erosion and Transportation of Materials by the River
Geography Erosion refers to the removal and wearing away of material from a wetted perimeter of a channel. Moving water uses its kinetic energy to erode surfaces. Erosion takes place through four processes. hydraulic, abrasion action, and attrition. An increase in velocity increases the operations of these processes and erosion occurs more effectively. There are three types of erosion that significantly affects the size of a river or stream. For instance, head ward erosion makes a river or stream longer. Vertical erosion on the other hand makes the river or stream channel deeper, while lateral erosion makes it wider. Erosion takes place hand in hand with transportation (Rodrigue, Comtois, and Slack: 132).
Transportation of materials in a stream or a river starts when water overcomes friction. Material that has been set loose through erosion is then transported along the stream. There are three main processes by which water in a stream or river transports material. suspension, traction and saltation, and solution (Rodrigue, Comtois, and Slack: 200). Suspension occurs when material composed of the finest particles such as silt and clay is lifted by the turbulence of water and transported away. Rivers that are more turbulent and fast-flowing carry more suspension. This explains why a stream or river gets muddy towards its mouth. The velocity of the water is greater here.
Traction and saltation occurs when larger particles are carried away. Saltation refers to when material such as gravel and pebbles that are too heavy to be carried away in suspension are bounced along by the water force. Traction on the other hand occurs when larger material like boulders is pushed and rolled along the river or stream bed by the force of the water. The third process, solution, occurs when materials such as minerals and dissolving rocks dissolve in the water and are carried along. This happens mostly in areas whose geology is limestone with water that is slightly acidic.
Stream capacity refers to the sum capacity of residue that a stream can move, transport, or carry. Water streams carry sediment. Different streams carry different amounts of sediment. This capacity depends on the velocity and volume of water that is being channeled. Stream competence on the other hand refers to the sedimentary particle size that a stream can move, transport, or carry (Gabler, Petersen, and Trapasso: 498). Again, each stream has its competency for the sedimentary particle size it can move by its velocity and volume. This competency changes with changes in velocity and stream volume. Such changes are caused by a variety of topography factors and seasonal flooding.
The difference between stream competence and stream capacity is that, while capacity gauges the quantity or amount of sentiment a river or stream can carry, competence gauges the size of sentiment particles (Gabler, Petersen, and Trapasso: 498). Sedimentary particles carried by streams include. boulder, pebble, rock, silt, sand, and clay. All these sediment particles vary in size. Normally, channelized rivers and streams are influence by gravitational force. The major factors that influence stream competence (size of sediment particle) and stream capacity (amount or quantity of sediment) is channel slope. Channel slope therefore, derives the measurements for stream gradient.
Gabler Robert, Petersen James, and Trapasso L. Essentials of Physical Geography. New York: Cengage Learning. 2006. 231-600. Print.
Rodrigue Jean, Comtois Claude, and Slack Brian. The Geography of Transport Systems. New York: Cengage Learning. 2013. 1-400. Print.