Question

Construction of a subsurface drainage system should begin from

• A. Outlet
• B. Laterals
• C. Far end of the outlet
• D. Anywhere in the field as per topography

Hint:

Drainage construction golden rule: Always start at the OUTLET and work UPSTREAM so the trench drains freely during construction.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Subsurface tile drain installation must follow a strict downstream-to-upstream sequence to maintain continuous gravitational trench dewatering during excavation.

Step 2: Detailed Explanation:
Standard civil and drainage engineering installation practice:
Construction and pipe laying of a subsurface drainage network must always start at the Outlet and proceed progressively upstream (Outlet $\rightarrow$ Main Collector Drain $\rightarrow$ Sub-mains $\rightarrow$ Laterals).
This ensures that:
1. Any groundwater seepage entering the trench during excavation drains out immediately by gravity.
2. Pipe grade and invert elevations are accurately established relative to the permanent outlet datum.

Step 3: Final Answer:
Therefore, construction should begin from the Outlet, matching option (A).