Question

In which layout subsurface drains enter the main drain at an angle ?

• A. Parallel system
• B. Double main system
• C. Random system
• D. Herringbone system

Hint:

Remember:
- Grid/Parallel system = Laterals enter at $90^\circ$ (right angles).
- Herringbone system = Laterals enter at an acute angle.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Subsurface drainage systems are laid out in different patterns depending on the topography of the field and the location of wet areas.
Detailed Explanation:
Let us analyze the common drainage layouts:
- Parallel system (A): Laterals are placed parallel to each other and enter the submain or main drain at right angles ($90^\circ$).
- Double main system (B): Used when a natural valley or depression runs through the field; two main lines are laid on either side of the valley to collect water from laterals.
- Random system (C): Used for undulating land where only scattered wet spots need drainage; drains are placed randomly without a uniform pattern.
- Herringbone system (D): Laterals enter the submain or main drain from both sides at an acute angle (less than $90^\circ$, typically $45^\circ$-$60^\circ$). The layout resembles the skeleton of a herringbone fish.

Step 2: Final Answer:
The layout where drains enter at an angle is the Herringbone system, which corresponds to Option (D).