WMS:Customized Lag Time Equation

Almost all of the lag time equations are of the form:

$T_{LAG}=C_{t}\ast \left({\frac {(L\ast L_{ca})}{\sqrt {S}}}\right)^{m}$

where:

T_LAG = watershed lag time in hours.

C_t = coefficient accounting for differences in watershed slope and storage.

L = the maximum flow length of the watershed along the main channel from the point of reference to the upstream boundary of the watershed, in miles.

L_ca = the distance along the main channel from the point of reference to a point opposite the centroid, in miles.

S = slope of the maximum flow distance path in ft/mile.

m = lag exponent

Therefore, if the equation the state, county, etc. uses to compute lag time is not available, it can often be set up using this equation by entering a custom coefficient, C_t, and exponent, m.

Related Topics

• Computing Lag Time or Time of Concentration from Basin Data