Section 4: Soil and Water Conservation Engineering
Hydrology
Subtopic: Hydrograph analysis, unit hydrograph theory and application
Question Statement:
[Linked 54–55] Assuming the above 1-h unit hydrograph to be triangular in shape with time to peak 1 hour, the peak of the 2-h unit hydrograph for the catchment in m³ s⁻¹ is
Options:
(A) 13.25
(B) 18.75
(C) 21.25
(D) 26.75
Official Answer Key:
B
Step-by-Step Solution & Explanation
The 2-h UH is obtained by lagging the 1-h UH by 1 hour and averaging the two ordinates (S-curve/superposition method). Taking a standard triangular shape with rise 0→1 h and recession 1→3 h (base = 3×time-to-peak), the ordinates of the original and the 1-h-lagged UH are summed and averaged; the resulting combined hydrograph peaks at t = 2 h, where U₁(2 h)=0 (already receded to zero... ) combined with the shifted curve's peak contribution gives a peak value of 18.75 m³/s, obtained directly from superposing the two 25 m³/s triangular ordinates offset by 1 hour and halving.
Section 5 — Irrigation and Drainage Engineering
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