Siphon-aqueduct design practice: What is the usual limiting velocity range (in m/s) adopted for drainage water flowing through the barrels of a siphon-aqueduct to avoid excessive head loss, vibration, and abrasion?

Introduction / Context:
Siphon-aqueducts convey drainage (or canal) water under pressure through barrels beneath another channel. Designers must limit velocity inside the barrels to balance economy with safety, avoiding excessive head loss, cavitation risk, abrasion, and structural vibration.

Given Data / Assumptions:

• Flow is closed-conduit through siphon barrels.
• Typical design guidance for permissible velocities in concrete or RCC barrels.
• Drainage water may carry some sediment; smoother barrels reduce losses.

Concept / Approach:
In pressure conduits, head loss varies roughly with velocity squared via friction and minor-loss coefficients. Excessively low velocity enlarges barrel sizes uneconomically; too high velocity increases losses and erosion. A pragmatic range is therefore selected.

Step-by-Step Solution:
Select a velocity band that limits friction and wear yet keeps barrel sizes reasonable.Common manuals recommend ~3–4 m/s for RCC/finished surfaces with moderate sediment load.Thus the normally limited velocity in siphon-aqueduct barrels is 3 to 4 m/s.

Verification / Alternative check:
Compare with permissible velocities for concrete lined conduits in water-resources handbooks: values around 2.5–4 m/s are commonly adopted, with 3–4 m/s widely used for economic designs.

Why Other Options Are Wrong:

• 1–2 m/s: Overly conservative; increases barrel size.
• 2–3 m/s: Possible but often leads to larger sections than necessary.
• 4–5 m/s: Can be uneconomical and may raise abrasion/vibration concerns.
• None of these: Not applicable because 3–4 m/s is a standard range.

Common Pitfalls:
Ignoring minor losses at entries and bends; not accounting for sediment abrasion; selecting velocity solely on friction tables without constructability and maintenance considerations.

Final Answer:
3 to 4 m/s