References on time of concentration with respect to sheet flow

For a surface of dense grass, n = 0.24, and slope of 0.02 ft/ft, the maximum length of sheet flow would be 59 ft (corresponding to a value of nL/(S of 100). Inserting these values into the TR-55 sheet flow travel time equation and assuming the 2-year 24 hour rainfall is 3 inches, the travel time would be 0.16 hour. ................
................