The rational formula for peak discharge from a small catchment is Q = C x I x A / 360 (in SI units of m3/s with A in hectares and I in mm/hour). The time of concentration tc is the:
Choose the correct answer
Time for flood peak to travel from outlet to furthest point
Time for runoff from the remotest point of the catchment to reach the outlet
Storm duration only
Time for 50% of rainfall to generate runoff
Correct Answer
B. Time for runoff from the remotest point of the catchment to reach the outlet
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tc = time of concentration = time for runoff from the most remote point to reach the outlet. For design, storm duration = tc (to maximize Q). Kirpich formula: tc = 0.0195 L^0.77 / S^0.385 (tc in min, L = length in m, S = slope).
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