See Equation at http://www.kssos.org/pubs/register%5C2007%5CVol_26_No_18_May_3_2007_p_607-676.pdf
Where
Tc = the time of concentration, in hours
L = the longest distance that water has to travel in the drainage basin, in miles
H = the maximum elevation difference in the drainage basin, in feet.
Kan. Admin. Regs. § 5-40-30