WMS:Eagleson Lag Time Equation

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Eagleson’s method (1962) for computing lag time in completely storm-sewered watersheds is given as follows:

File:Image116.gif

where:

TLAG - watershed lag time in hours.

L - maximum flow length in miles.

Lca - length to the centroid in miles.

S - weighted average slope of the maximum flow path in ft/mile.


The typical characteristics of watersheds for which the Eagleson method was applied include the following:

  • Areas from 0.22 to 7.5 square miles.
  • L from 1 to 7 miles.
  • Lca from 0.3 to 3 miles.
  • S from 6 to 20 ft/mile.
  • Impervious cover from 33 to 83 percent.


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