The depths from the soil surface to subsurface tile drains, impermeable soil layer and the highest water table are measured as 2.8 m, 5.0 m and 0.8 m, respectively. The effective hydraulic head for drainage in meter is
Options:
(A) 0.8
(B) 2.0
(C) 2.2
(D) 4.2
Official Answer Key:
B
Step-by-Step Solution & Explanation
The effective (driving) head for subsurface drainage is the height of the water table above the drain centre (m in the Hooghoudt notation).
h = (depth to drain) − (depth to highest water table) = 2.8 − 0.8 = 2.0 m.
Distractor (C) 2.2 = 5.0 − 2.8 is the depth of the impermeable layer below the drain (Hooghoudt's d), not the head; (D) 4.2 = 5.0 − 0.8.
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