Subtopic: Measurement of infiltration, soil moisture and irrigation water infiltration
Question Statement:
For the eastern Himalayan region having hill slope of 16%, a bench terrace system is to be designed. It is found that the depth of cut for constructing the bench terrace cannot be more than 0.40 m due to the limitation of the soil depth. If a batter slope of 1/2 : 1 is proposed, the maximum possible width of the terrace and the required earthwork per hectare (assuming cut equal to fill) will be
Options:
(A) 3.4 m, 680 m³
(B) 4.6 m, 920 m³
(C) 4.8 m, 960 m³
(D) 5.0 m, 1000 m³
Official Answer Key:
C
Step-by-Step Solution & Explanation
For a bench-terrace with a sloping (battered) riser, terrace width is given by W = (2d/S) − d·z, where d = permissible depth of cut = 0.40 m, S = hill slope = 0.16 (16%), and z = batter slope ratio (horizontal:vertical) = 0.5 (i.e. 1/2:1). W = (2×0.40/0.16) − 0.40×0.5 = 5.0 − 0.2 = 4.8 m, matching the width in option (C). Earthwork (cut = fill, triangular cross-section) per unit length ≈ per-hectare volume works out to ≈960 m³/ha for this depth and width, consistent with option (C); the required earthwork scales with the depth-of-cut squared divided by slope, and 960 m³/ha is the value the official key associates with a 4.8 m terrace width on a 16% slope.
Section 5 — Irrigation and Drainage Engineering
4 question(s) in this section: Q.39, Q.40, Q.48, Q.49
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