Section 4: Soil and Water Conservation Engineering
Hydrology
Subtopic: Hydrological cycle and measurement of its components
Question Statement:
Thickness of capillary zone above the water table varies
Options:
(A) linearly with the pore-size of soil
(B) inversely with the height of water table
(C) linearly with the height of water table
(D) inversely with the pore-size of soil
Official Answer Key:
D
Step-by-Step Solution & Explanation
• The capillary fringe above a water table behaves like a bundle of capillary tubes; capillary rise h is governed by h = 4σcosθ/(γd) (or, equivalently, h ∝ 1/pore radius) — the classic capillary-rise relation.
• Finer pore soils (small pores/small effective tube diameter) draw water higher due to greater capillary suction, so the capillary-zone thickness increases as pore size decreases — an inverse relationship.
• Final Answer: (D) inversely with the pore-size of soil
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