WMS:Eagleson Lag Time Equation

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

$T_{LAG}=0.32\left({\frac {L\ast L_{ca}}{\sqrt {S}}}\right)^{0.39}$

where:

$T_{LAG}$ = watershed lag time in hours.

$L$ = maximum flow length in miles.

$L_{ca}$ = 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.
• $L_{ca}$ from 0.3 to 3 miles.
• $S$ from 6 to 20 ft/mile.
• Impervious cover from 33 to 83 percent.

Related Topics

• Computing Lag Time or Time of Concentration from Basin Data