Subtopic: Leaching requirement and salinity control
Question Statement:
The nature of Hooghoudt's equation for drain spacing is
Options:
(A) Parabolic
(B) Hyperbolic
(C) Elliptic
(D) Circular
Official Answer Key:
C
Step-by-Step Solution & Explanation
Hooghoudt's steady-state drain-spacing equation, S² = 4Kd·d(2De+d)/q (with De the Hooghoudt equivalent depth), is derived by combining radial flow near the drain, idealised as flow through confocal ellipses (elliptical flow-net near the drain), with horizontal (parallel) flow further away. This elliptical-flow-net basis is why the equation's derivation/character is classically described as elliptic, matching option (C), rather than the other listed conic-section shapes.
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