WMS:Customized Lag Time Equation: Difference between revisions

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where:
where:


<math>T_{LAG}</math> = watershed lag time in hours.
''T<sub>LAG</sub>'' = watershed lag time in hours.


<math>C_t</math> = coefficient accounting for differences in watershed slope and storage.
''C<sub>t</sub>'' = coefficient accounting for differences in watershed slope and storage.


<math>L</math> = 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'' = 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.


<math>L_{ca}</math> = the distance along the main channel from the point of reference to a point opposite the centroid, in miles.
''L<sub>ca</sub>'' = the distance along the main channel from the point of reference to a point opposite the centroid, in miles.


<math>S</math> = slope of the maximum flow distance path in ft/mile.
''S'' = slope of the maximum flow distance path in ft/mile.


<math>m</math> = lag exponent
''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, <math>C_t</math>, and exponent, <math>m</math>.
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<sub>t</sub>'', and exponent, ''m''.




Revision as of 15:56, 7 December 2016

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

where:

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.


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