GATE CE 2025 Set 1 — Question 43
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Water Resources Engineering → Canals & Hydraulic Structures → Unlined Canals
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Question
Lacey’s regime equations, followed in India for making scour calculations while designing hydraulic structures across alluvial channels, are given below.
Regarding these equations, which of the following statements is/are true:where, is discharge and is silt factor.
Regarding these equations, which of the following statements is/are true:where, is discharge and is silt factor.
Correct answer
(B) P is the Lacey’s waterway width; (D) D is the depth of scour below the design flood level
Solution
In Lacey's regime theory:
1. is the regime wetted perimeter. For wide alluvial channels, the wetted perimeter is approximately equal to the waterway width. Thus, statement (B) is true.
2. represents the regime depth (hydraulic mean depth). In the context of scour calculations for hydraulic structures, this depth is measured from the High Flood Level (HFL) or design flood level. Thus, statement (D) is true and (A) is false.
3. is the silt factor where is the average grain size diameter in millimetres (mm), not centimetres. Thus, statement (C) is false.
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