ANS:B - unsteady non-uniform

Water flow in a river during a flood can be categorized as unsteady non-uniform flow.

• Unsteady Flow: This type of flow refers to a situation where the flow variables, such as velocity, discharge, and depth, change with respect to time. During a flood event, the flow in a river undergoes significant changes over time as the water level rises and falls, making it an unsteady flow.
• Non-uniform Flow: Non-uniform flow refers to a flow situation where the velocity of the flow varies across different sections of the channel. In a river during a flood, the velocity of the water is likely to vary spatially across the cross-section of the river due to changes in channel morphology, bed roughness, and flow obstructions, making it non-uniform.