Question

Describe the reason that the process of degradation occurs only at higher velocities than transportation, regardless of particle size.

Answer 1

Answer:-The term degradation refers to the erosion process of removing sediments from the stream bed and banks. Faster stream flow velocities are necessary for degradation to take place. Aggradation refers to the deposit of sediments. Slower stream flow velocities are necessary for aggradation to take place. Notice on the graph provided that higher velocities are necessary to dislodge materials (degradation) than to transport materials already being carried by a river.Large rivers in humid environments are frequently found within a floodplain, or broad flat region bordering the channel of a river. The generally flat terrain of a floodplain results in a slow-moving river with a meandering channel form. The constant process of aggradation and degradation operating along its meanders causes the river bends to move across the floodplain over time. This process begins with the enlargement of a particular meander through the degradation occurring on the outside of the river bend and the deposition of material on the inside of the bend. Over time the meander will tend to move in the direction of the outside of the river bend, altering the entire course of the river in that area. Additionally, if the bend becomes increasingly narrow over time, the river may form a cutoff that separates the bend from the rest of the river, forming an oxbow lake. Lastly, any oxbow lake or other abandoned meander that fills with sediment will result in the formation of distinctive meander scars. In addition, frequent small flood events may alter the height of the banks of the rivers by depositing sediments carried overbank the flooding river. While the velocity of the river within its channel prevents the aggravation of such material, the moment the river water begins to flow across its floodplain, the water velocity decreases rapidly, resulting in the deposition of additional sediment on either bank of the river. These deposits are referred to as natural levees as they serve to inhibit future frequent small-scale flooding events as a result of the increasing height of the river banks.

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