WMS:Putnam Lag Time Equation

Putnam (1972) developed a lag equation for watersheds around the Wichita, Kansas area as follows:

$T_{LAG}=0.49{\sqrt {\frac {L}{\sqrt {S}}}}I_{a}^{-0.57}$

where:

T_LAG = lag time in hours.

L = maximum flow length in miles.

S = weighted slope along the maximum flow path in ft/mile.

I_a = Impervious cover as a fraction.

This equation was used for watersheds ranging in size from 0.3 to 150 sq. miles, impervious covers less than 0.3 and a ratio of between 1.0 and 9.0.

Related Topics

• Computing Lag Time or Time of Concentration from Basin Data