Analytical calculation of the gradient involves plugging in each of the parameters derived from each level of parameter extraction into the SCS lag equation, shown in Equation 5.4, while holding the other parameters constant.
tlag (min) =
C N 9 1 0 0 0 7 . 0 8 31.67 . 0 ⎟ ⎠ s ⎞ ⎜ ⎝ ⎛ −
In Equation 5.4, Lw is longest flow path in units of feet, and slope is expressed as a percentage. Curve number is symbolized by CN, and tlag is the lag
time in minutes.
These numbers are the mean
outlines the base values calculated
values used for these calculations. for Area 2, as shown previously in
Table 5.2 and Table 5.4.
Table 5.5: Parameter Base Values
184.108.40.206 Longest Flow Path
To evaluate changes in SCS lag time that result from changes in the longest flow path, the curve number and average slope were held constant while