WMS:Putnam Lag Time Equation

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

File:Image118.gif

where:

TLAG - lag time in hours.

L - maximum flow length in miles.

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

Ia - 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.


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