Section 4: Soil and Water Conservation Engineering
Hydrology
Subtopic: Drought and its classification
Question Statement:
Hydrology: Hydrological cycle and measurement of its components; meteorological parameters and their measurement; analysis of precipitation data; runoff estimation; hydrograph analysis, unit hydrograph theory and application; stream flow measurement; flood routing, hydrological reservoir and channel routing, Infiltration – indices and equations, drought and its classification.
The peak of a flood hydrograph due to a 5-hour storm is 670 m³ s⁻¹. Total depth of rainfall is 9 cm. Assuming average infiltration loss of 0.2 cm h⁻¹ and constant baseflow of 30 m³ s⁻¹, the peak discharge of the 5-hour unit hydrograph for this catchment in m³ s⁻¹ is ______.
Official Answer Key:
80 to 80
Step-by-Step Solution & Explanation
Direct runoff peak = total hydrograph peak − baseflow = 670 − 30 = 640 m³/s.
Effective rainfall (runoff-producing depth) over the 5-hour storm = total rainfall − infiltration loss = 9 − (0.2 × 5) = 9 − 1 = 8 cm.
By definition, a unit hydrograph corresponds to 1 cm of effective rainfall, so scaling linearly:
UH peak = Direct runoff peak / effective rainfall (cm) = 640/8 = 80 m³/s. Answer: exactly 80.
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