Question

Given below are two statements, one is labelled as Assertion A and the other is labelled as Reason R:
Assertion A: The Cipoletti weir is a trapazoidal weir used for the measurement of flow in irrigation channel.
Reason R: It does not require corrections for end contractions and commonly used for high discharge measurement.
In light of the above statements, choose the most appropriate answer from the options given below:

• A. Both A and R are correct and R is the correct explanation of A
• B. Both A and R are correct but R is NOT the correct explanation of A
• C. A is correct but R is not correct
• D. A is not correct but R is correct

Hint:

Remember the Cipoletti weir specifications:
- Shape: Trapezoidal.
- Side Slope: 1 Horizontal to 4 Vertical (compensates for end contractions).
- Flow Formula: $Q = 1.86 \cdot L \cdot H^{1.5}$ (no correction terms required).

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Weirs are overflow structures built across open channels to measure water flow.
A standard rectangular weir experiences "end contractions," where the water flow contracts laterally as it passes through the weir sides.
This contraction reduces the effective width of the flowing water column, requiring a correction factor in the flow equations.
The Cipoletti weir was specifically designed to simplify these calculations.

Step 2: Detailed Explanation:
Let us analyze the design and hydraulics of the Cipoletti weir:
1. Assertion A: The Cipoletti weir is a trapezoidal weir used for the measurement of flow in irrigation channel.
This statement is correct.
The Cipoletti weir is a trapezoidal weir named after the Italian engineer Cesare Cipoletti.
It is commonly used in irrigation canals to measure water delivery.
Therefore, Assertion A is true.
2. Reason R: It does not require corrections for end contractions and commonly used for high discharge measurement.
This statement is correct.
The Cipoletti weir is designed with specific sloped sides having a ratio of $1$ horizontal to $4$ vertical ($1:4$ slope, or approximately $14^{\circ}$).
This trapezoidal shape is geometrically designed so that the additional flow passing through the triangular side sections exactly compensates for the reduction in flow caused by end contractions.
This eliminates the need to apply end contraction corrections to the flow equation, simplifying it to a standard rectangular form:
\[ Q = 1.86 \times L \times H^{1.5} \] Because this design simplifies field calculations while maintaining high accuracy for large flows, it is widely used for high-discharge measurements in open canals.
Since this unique hydraulic design feature (Reason R) explains why the Cipoletti weir is constructed as a trapezoid (Assertion A), Reason R is the correct explanation of Assertion A.

Step 3: Final Answer:
Both Assertion A and Reason R are true, and Reason R is the correct explanation of Assertion A.
Hence, the correct option is (A).