Time of Concentration Calculator

Calculate time of concentration (Tc) using multiple methods including Kirpich, FAA, NRCS Lag, Kerby-Hathaway, and TR-55 segmental approach. Essential for hydrologic analysis and drainage design.

Calculation Method

Best for: Small agricultural watersheds with overland and channel flow. Developed from data on Tennessee watersheds.

Input Parameters

Flow Path Properties

Enter the characteristics of the longest flow path

ft

Length of the longest flow path from watershed divide to outlet

ft

Difference in elevation between the divide and outlet

Which Method Should I Use?

Kirpich

  • - Small agricultural watersheds
  • - Natural channels
  • - Simple preliminary estimates

FAA

  • - Airport drainage
  • - Parking lots
  • - Small impervious areas

NRCS Lag

  • - SCS hydrograph methods
  • - Rural watersheds
  • - When CN is known

Kerby-Hathaway

  • - Overland flow only
  • - Natural surfaces
  • - Flow length under 1000 ft

TR-55 Composite

  • - Complex flow paths with multiple segments
  • - Urban and rural watersheds
  • - Most accurate for varied terrain
  • - Required for detailed drainage design
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