02
Time of concentration
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The result will show estimated Tc and canonical inputs.
Estimate a single-segment channel-flow time of concentration using the FHWA HDS-2 Kirpich equation with SI/US inputs.
Enter inputs and calculate.
The result will show estimated Tc and canonical inputs.
TOOL-004 uses the FHWA HDS-2 Kirpich channel-flow travel-time relationship: Tc = 0.0195 × L^0.77 × S^-0.385 in SI, with L in metres, S in m/m, and Tc in minutes.
Kirpich is an empirical relationship for channel flow. FHWA HDS-2 notes that it was developed from small drainage basins of about 1–112 acres and describes channel-flow use where gullying or engineered conveyance is evident in more than 10% of the primary watercourse. This V1 treats the Kirpich channel travel time as Tc only when the controlling hydraulic path can reasonably be represented by a single channel-flow segment. Otherwise, use a segmented travel-time method that sums the applicable flow components.
For L = 300 m and S = 0.02 m/m, the Kirpich channel travel time is approximately 7.1043 minutes. Under the single-segment assumption used by TOOL-004 V1, this is reported as the estimated Tc.
TOOL-004 does not compute rainfall intensity, Rational Method runoff, sheet-flow roughness, channel velocity, detention routing, pipe capacity or network hydraulics. The result does not automatically establish local-code or permit compliance.
Primary method source: FHWA Highway Hydrology (HDS-2), Third Edition, represented as SRC-KIRPICH-FHWA-HDS2-TOOL004-001.