Multiple choice

The top width and the depth of flow in a triangular channel were measured as 4 m and 1 m, respectively. The measured velocities on the centre line at the water surface, 0.2 m and 0.8 m below the surface area 0.7 m/s, 0.6 m/s and 0.4 m/s respectively. Using two point method of velocity measurement, the discharge (in m3/s) in the channel is

  1. 1.4

  2. 1.2

  3. 1.0

  4. 0.8
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C Correct answer
Explanation

The two-point method uses velocities at 0.2d and 0.8d. Average velocity V_avg = (V_0.2 + V_0.8) / 2 = (0.6 + 0.4) / 2 = 0.5 m/s. Area of triangular channel = 0.5 * base * height = 0.5 * 4 * 1 = 2 m^2. Discharge Q = A * V = 2 * 0.5 = 1.0 m^3/s.

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