Time of Concentration (Kirpich)

t_{c} = 0.0078 L^{0.77} S^{- 0.385} (t_{c} min, L ft, S ft/ft)

tc is the travel time from the hydraulically most distant point. Rational Q=CiA uses i for duration tc. Other formulas (FAA, kinematic wave) appear in the handbook — match units.

$L$ (ft): Longest flow path
$S$: Average slope of that path

Step-by-step solved example

L=500 ft, S=0.01. Kirpich tc?

Longest path L on the catchment — tc from Kirpich.

1. Powers
500^{0.77}≈121, 0.01^{-0.385}≈5.21.
2. tc
0.0078×121×5.21≈4.9 min.

Answer: tc ≈ 5 min

10 practice questions

0/10 correct

1.Longer L makes tc

2.Steeper S makes tc

3.Rational i is read from an IDF curve at duration

4.C in Q=CiA is

5.Units trap: Kirpich L in

6.Overland + channel tc is

7.NRCS lag is about 0.6 tc in

8.If S=0.04 vs 0.01, S^{-0.385} ratio is

9.Urbanization generally

10.A code minimum tc (e.g. 5 or 10 min) exists because