The Lowest Elevation and Deepest Part of a Stream
What is the lowest elevation to which a stream can downcut? What is the deepest part of the channel where the stream flows fastest?
Answer:
The lowest elevation to which a stream can downcut is the base level. The deepest part of the channel, where the stream flows fastest, is the thalweg.Explanation:
The lowest elevation to which a stream can downcut is called the base level. This is the point at which the stream cannot erode any further because it has reached the lowest point in its surroundings, such as the ocean or a lake. The deepest part of the stream channel, where the water flows fastest, is called the thalweg. This is typically located in the center of the channel where the water is deepest and has the least resistance from the stream banks.
As a stream progresses from its source to its mouth, there are changes in the channel width and water speed. Near the source, the stream is typically narrow and fast-flowing, often due to a steep gradient, while towards the mouth, as the gradient decreases and tributaries contribute to the flow, the river widens and the current slows down.
An experiment to observe this is to drop two sticks into a river, one near the edge and one in the middle. The stick in the middle, or near the thalweg, will travel faster, demonstrating the speed variance within the stream's channel.