Which sub-surface drainage system consists of laterals that enter the main drain at an angle, generally from both sides?

Correct option is D

✅ (d) Herringbone
· Herringbone drainage system has laterals entering the main drain at an angle from both sides, resembling a fish skeleton.
· Suitable for areas with a central depression or valley.
· Effective for uniform water table control in wide fields.
❌ (a) Interceptor
· Interceptor drains are placed across slopes to intercept seepage water, not designed in a herringbone pattern.
· Incorrect layout type.
❌ (b) Gridiron
· Gridiron systems consist of parallel laterals perpendicular to the main drain.
· No angled entry from both sides.
❌ (c) Random
· Random systems are irregularly laid out to drain isolated wet spots.
· No systematic angle of entry.