WMS:Customized Lag Time Equation
Almost all of the lag time equations are of the form:
- TLAG = watershed lag time in hours.
- Ct = 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.
- Lca = 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, Ct, and exponent, m.
WMS – Watershed Modeling System
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