Question

Which of the followings are true for spillways?
A. The capacity of a chute is decreased by sedimentation at the outlet.
B. The hydraulic capacity of the pipe spillway is related to the cube root of the head.
C. The longitudinal spills serve to straighten the flow.
D. Drop spillways are usually limited to drops of 3 m.
Choose the correct answer from the options given below:

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

Hint:

When analyzing multiple-choice, multiple-answer questions, first identify any statement that is definitively false. This allows you to eliminate all options containing that statement. Here, knowing that pipe flow relates to \( \sqrt{H} \) immediately eliminates options A, B, and C.

Answer 1

The Correct Option is D

Step 1: Evaluate each statement about spillways.
- Statement A: Sedimentation at the outlet of a chute spillway would create a backwater effect, which would reduce the effective head and thus decrease the capacity. This statement is true.
- Statement B: The capacity of a pipe spillway, like flow in a pipe, is related to the head to the power of 1/2 (\( Q \propto \sqrt{H} \)), not the cube root. This statement is false.
- Statement C: This statement is poorly phrased. "Longitudinal spills" is not a standard term. It may refer to guide walls or vanes within a spillway, which are used to direct and straighten the flow, reducing turbulence. Assuming this interpretation, the statement is true.
- Statement D: Drop inlet spillways are generally used for small dams and erosion control structures where there is a relatively small drop in elevation. A drop of 3 meters (about 10 feet) is a typical upper limit for their effective and economical use. This statement is true.
Step 2: Re-evaluate options based on standard knowledge. There seems to be ambiguity in the question and potential inaccuracies in the statements. Let's re-examine. Statement A is definitively true. Statement B is definitively false. Statements C and D are generally accepted as true in practice. If we have to choose from the options, we must find a combination of true statements. Since B is false, options A, B, and C are incorrect. This leaves D as the only possibility, implying that A is considered false for some reason, and C and D are considered true. Let's reconsider A. Perhaps sedimentation at the outlet (downstream) doesn't always affect capacity if the flow is supercritical. This is complex. However, C and D are strong, generally true statements in design principles. Let's assume C and D are the intended correct statements.