Uniform flow is said to occur when

ANS:A - size and shape of the cross-section in a particular length remain constant

When we say that the size and shape of the cross-section in a particular length remain constant, we are referring to the consistent dimensions and geometry of the channel over that length of the channel. Here's a breakdown of what this means:

1. Size of the Cross-section: The size of the cross-section refers to the area enclosed by the channel's boundaries, typically represented by the width and depth of the channel. In uniform flow, the width and depth of the channel do not change along the specified length. This means that the cross-sectional area of the channel remains the same.
2. Shape of the Cross-section: The shape of the cross-section refers to the geometric configuration of the channel, such as trapezoidal, rectangular, or triangular. In uniform flow, the shape of the channel remains consistent along the specified length. This means that the proportions and angles defining the shape of the channel do not change.
3. Constant Dimensions: Throughout the specified length of the channel, the dimensions—both width and depth—remain constant. There are no abrupt changes or variations in the physical characteristics of the channel that would alter the flow conditions.
4. Uniform Flow Parameters: With the size and shape of the cross-section remaining constant, the flow parameters such as velocity, depth, and discharge also remain consistent along the specified length. This uniformity simplifies hydraulic calculations and analysis.

In practical terms, ensuring that the size and shape of the cross-section remain constant allows engineers to apply simplified flow models and equations to analyze and design hydraulic structures and systems. It provides a basis for predicting flow behavior and performance under various conditions while facilitating efficient and accurate engineering solutions.