WMS:Riverside County Lag Time Equation

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The Riverside County Flood Control and Water Conservancy District developed three different lag equations corresponding to mountainous, foothill, and valley areas near Riverside County, California (Anonymous, 1963).

T_{LAG} = 1.20 \left ( \frac {L \ast L_{ca}}{ \sqrt {S}} \right )^{0.38}
(Mountainous) 15.19
T_{LAG} = 0.72 \left ( \frac {L \ast L_{ca}}{ \sqrt {S}} \right )^{0.38}
(Foothills) 15.20
T_{LAG} = 0.38 \left ( \frac {L \ast L_{ca}}{ \sqrt {S}} \right )^{0.38}
(Valleys) 15.21

where:

TLAG = lag time in hours.
L = maximum flow length in miles.
Lca = length to the centroid in miles.
S = weighted slope along the maximum flow path length in ft/mile.

The typical characteristics of watersheds for which the Riverside County equations were used include the following:

  • Areas from 2 to 650 square miles.


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