Smooth entry alignment — the recommended angle between the head regulator axis and the direction of river flow for a canal offtake is generally kept close to:

Introduction / Context:
At the river–canal junction, proper alignment of the head regulator relative to the river flow reduces entry losses, avoids excessive sediment ingress, and provides stable approach hydraulics. Design manuals recommend a range for the included angle to balance smooth entry with site constraints.

Given Data / Assumptions:

• Canal offtake from a river via a head regulator.
• Objective: minimize approach separation, vortices, and sediment draw.
• Standard practice suggests an obtuse angle between canal axis and river flow.

Concept / Approach:

Aligning the canal approximately downstream and at an oblique angle to river flow (often recommended around 110°) yields smoother entry and better sediment exclusion than a sharp right-angle takeoff. Too small or too large angles can induce unfavorable eddies or head losses.

Step-by-Step Solution:

Verification / Alternative check (if short method exists):

Model studies (physical or CFD) often find a sweet spot slightly obtuse to the river direction; many projects adopt values near 110° when feasible.

Why Other Options Are Wrong:

80°/90° produce sharper bends and more entry loss; 120° might over-align downstream and is less commonly cited as the baseline recommendation; 150° is excessive.

Common Pitfalls (misconceptions, mistakes):

Confusing this angle with bend angle inside the canal; ignoring local bathymetry and approach flow skew that may require fine-tuning.

Final Answer:

110°