Question

Which of the following statement(s) is/are correct
(A). In designing field channels, the flow is considered to be uniform at the maximum discharge.
(B). Flows in lined irrigation channel tend to be steady.
(C). Flows in lined irrigation channel tends to be steady and uniform.
(D). In a channel of changing cross-section, the flow is non-uniform.
Choose the correct answer from the options given below:

• A. (A) and (C) only
• B. (A) and (D) only
• C. (B), (C) and (D) only
• D. (A), (B) and (D) only

Hint:

To analyze open channel flow types:
- Constant cross-section + Constant discharge \(\rightarrow\) Uniform flow.
- Changing cross-section \(\rightarrow\) Non-uniform (varied) flow (since area \(A\) changes, velocity \(V\) must change spatially).
- Constant parameters with time \(\rightarrow\) Steady flow.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Open channel flow is classified as steady or unsteady based on temporal variations (changes over time), and as uniform or non-uniform (varied) based on spatial variations (changes along the channel length).

Step 2: Detailed Explanation:
Let us analyze the correctness of each statement individually:
- Statement (A) is correct:
Field channels (such as irrigation watercourses) are designed to convey a maximum required peak discharge.
For design purposes, the flow is assumed to be steady and uniform at this peak discharge, allowing the use of the Chezy or Manning equations to determine channel dimensions.
- Statement (B) is correct:
Lined irrigation channels have rigid boundaries with a fixed cross-section and constant slope.
Under a stable regulatory supply, the discharge remains constant over time, meaning the flow tends to be steady.
- Statement (C) is partially incorrect less appropriate:
While the flow in a lined channel can be uniform, it is not always guaranteed to be uniform throughout due to local control structures, inlets, or bends that can cause varied (non-uniform) flow.
Therefore, stating it "tends to be steady" is a more robust engineering assumption.
- Statement (D) is correct:
By definition, if the cross-section of a channel changes along its length, the velocity of flow must vary from point to point along the channel to satisfy the continuity equation (\(Q = AV\)).
This spatial variation in velocity means the flow is non-uniform (varied flow).
Thus, statements (A), (B), and (D) are correct.

Step 3: Final Answer:
The correct statements are (A), (B), and (D) only.