Subtopic: Planning, design and layout of surface and sub-surface drainage systems
Question Statement:
In agricultural subsurface drainage, corrugated plastic tubing is surrounded by an envelope/filter material primarily to:
Options:
(A) Prevent entry of fine soil particles into the drain and improve hydraulic permeability around the drain
(B) Increase chemical precipitation of iron and manganese compounds
(C) Prevent roots from extracting moisture from the soil profile
(D) Completely seal the perforated perforations against water entry
Answer Key:
A
Step-by-Step Solution & Explanation
Drain envelopes serve a dual function:
1. Filtration: Restraining fine silt and sand particles from washing through pipe perforations (preventing silting).
2. Bedding & Hydraulics: Increasing permeability immediately adjacent to the drain openings to reduce entrance head loss.