Correct Option: C. Shallow Explanation of the Correct Answer The term "broad" in the context of a river channel typically indicates that the river has a wide cross-section. When we consider the options provided, we need to analyze what each term means in relation to river morphology and flow characteristics.

1. Understanding River Channel Types:
2. Incised: An incised channel is one that has been cut deeply into the landscape, often due to erosion. This type of channel is usually narrow and steep-sided, which does not align with the description of a "broad" channel.
3. Graded: A graded river channel is one that has reached a state of equilibrium where the slope, sediment load, and flow are balanced. While a graded channel can be broad, the term does not specifically describe the width of the channel.
4. Shallow: A shallow channel indicates that the water depth is relatively low. A broad and shallow channel can occur in river systems where sediment deposition is significant, leading to a wide but not deep channel.
5. U-shaped: A U-shaped channel typically refers to a valley or a glacially formed channel that has a distinct U shape. This does not directly relate to the width of the river channel.

Given these definitions, the term "shallow" is the most appropriate descriptor for a broad river channel, as it suggests that while the channel is wide, it does not have significant depth. Why the Other Options are Incorrect

• A. Incised: As mentioned, incised channels are characterized by their depth and narrowness. A broad channel cannot be incised because incised channels are formed through significant erosion, leading to steep banks and a narrow width.
• B. Graded: While a graded channel can be broad, the term does not specifically indicate the channel's width or depth. It refers more to the balance of sediment transport and river flow, which does not directly correlate with the description of the channel being broad.
• D. U-shaped: This option refers to the shape of the valley or channel rather than its width or depth. U-shaped channels are typically associated with glacial activity and do not describe a broad channel effectively.

Summary of Key Points

• A broad river channel is typically shallow, indicating low water depth.
• Incised channels are narrow and deep, making them incompatible with the description of a broad channel.
• Graded channels refer to equilibrium in sediment transport and flow, not specifically to width or depth.
• U-shaped channels describe a specific valley shape, not the characteristics of width or depth.

Revision Summary

• A broad river channel is often shallow, indicating low depth.
• Incised channels are narrow and deep, not broad.
• Graded channels focus on equilibrium, not width.
• U-shaped channels describe valley shape, not channel characteristics.