Step 1: Understanding the Concept:
The question asks for the specific term that describes the erosion processes occurring within a defined stream or river channel. This is one of the major categories of water erosion.
Step 2: Detailed Explanation:
Let's define the different types of water erosion:
Splash Erosion: The initial detachment of soil particles caused by the impact of raindrops.
Sheet Erosion: The uniform removal of a thin layer of soil from the land surface by overland flow or runoff.
(D) Rill erosion: As runoff concentrates, it begins to cut small, well-defined channels called rills. These are small enough to be removed by normal tillage operations.
(B) Gully erosion: When rills are not addressed, they can grow larger and deeper, forming gullies. Gullies are too large to be removed by normal tillage and are a more advanced stage of erosion.
Stream Channel Erosion (or Stream Bank Erosion): This type of erosion occurs within the channels of permanent streams and rivers. It involves two main processes described in the question:
Scouring of material from the water channel: The flow of water scours and removes material from the bed (bottom) of the channel. This is also called channel bed degradation.
Cutting of banks by running water: The flow of water undercuts and erodes the sides (banks) of the channel, causing them to collapse. This is called bank erosion.
The term "Stream Channel erosion" perfectly encompasses both of these processes.
(A) Channel erosion is a more general term that could include rill and gully erosion. "Stream Channel erosion" is more specific to perennial streams and rivers. Given the options, "Stream Channel erosion" is the most precise answer.
Step 3: Final Answer:
The process of scouring the channel bed and cutting the banks of a stream or river is known as Stream Channel erosion. Therefore, option (C) is the correct answer.