Pressure conduits and conveyance works: Which statement below is INCORRECT in general water-supply practice?
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AIn a pressure conduit, the pipe invert need not follow the hydraulic gradient line; the HGL may lie above or below the pipe.
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BPressure conduits may be routed over local rises above the hydraulic grade line, provided negative pressures are within safe limits.
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CAqueducts (open-channel carriers) and tunnels are generally kept circular in section.
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DNone of these.
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EAll of these.
Answer
Correct Answer: Aqueducts (open-channel carriers) and tunnels are generally kept circular in section.
Explanation
Introduction / Context:Water-conveyance systems include pressure pipes, tunnels, and aqueducts. Section shapes and hydraulic controls differ depending on whether the flow is pressurized or open-channel. This question distinguishes typical practice from an incorrect generalization.
Given Data / Assumptions:
- Pressure pipes convey under head; alignment is not constrained by HGL grade.
- Tunnels may carry either open-channel or pressurized flow; circular shapes are common for pressure and structural reasons.
- Aqueducts in water-supply/irrigation typically operate as open channels (rectangular/trapezoidal), not circular.
Concept / Approach:Separate pressure systems from open-channel carriers. Circular is excellent for pressure (isotropic hoop strength), but open-channel aqueducts use noncircular prismatic sections that optimize free-surface flow, construction, and maintenance.
Step-by-Step Solution:
Evaluate (a): In pressure pipelines, invert can rise or fall; HGL governs energy, not necessarily pipe slope → essentially correct.Evaluate (b): Pipes may crest above HGL (siphon routing), provided vapor pressure constraints are respected → acceptable in principle.Evaluate (c): Tunnels may be circular, but aqueducts (open channel) are commonly trapezoidal/rectangular; calling both “generally circular” is incorrect.Verification / Alternative check:Design manuals illustrate aqueduct flumes as rectangular/trapezoidal concrete channels; pressure tunnels and steel liners are often circular for structural efficiency.
Why Other Options Are Wrong:Options (a) and (b) reflect accepted practice; “None/All” are distractors because (c) is demonstrably inaccurate as a blanket statement.
Common Pitfalls:Confusing pressure conduits with open channels; assuming circular sections are universal regardless of flow regime.
Final Answer:Aqueducts (open-channel carriers) and tunnels are generally kept circular in section.