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 that your state, county, etc. uses to compute lag time is not available, it can often be set up using this equation by entering your own coefficient, $C_{t}$, and exponent, $m$.

Related Topics

• Computing Lag Time or Time of Concentration from Basin Data