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GATE 2022 CE (CE1) – Question 21

Hydraulics · Gradually varied flow and water surface profiles · 1 mark · Multiple choice

A rectangular channel with Gradually Varied Flow (GVF) has a changing bed slope. If the change is from a steeper slope to a steep slope, the resulting GVF profile is

  1. S3
  2. S1
  3. S2
  4. either S1 or S2, depending on the magnitude of the slopes

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Show answer and explanation

Correct answer: (A) S3

Explanation

Both slopes are steep, so their normal depths lie below critical depth. The upstream **steeper** reach has the smaller normal depth.

On entering the less-steep downstream reach, that shallow supercritical flow has depth below the new normal depth: $y<y_n<y_c$. This is zone 3 on a steep slope, giving an **S3 profile (A)**.