The SCS dimensionless unit hydrograph expresses the unit hydrograph in terms of the ratio Q/Qp (ordinate ratio) vs t/Tp (time ratio). The peak flow Qp (m3/s per mm of runoff per km2) is related to the time to peak Tp (h) by:
Choose the correct answer
Qp = 2.08 x A / Tp (empirical, where A = catchment area in km2)
Qp = A x Tp
Qp = 0.208 / Tp
Qp = 2.78 / Tp
Correct Answer
A. Qp = 2.08 x A / Tp (empirical, where A = catchment area in km2)
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SCS dimensionless UH: Qp = 2.08 x A/Tp (A in km2, Tp in hours, Qp in m3/s per 10 mm of runoff). The factor 2.08 comes from: Qp = (2.083 x A x RO) / Tp for 1 mm runoff over A km2. The dimensionless UH shape (37.5% of runoff before Tp) is universal for all catchments.
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