Return Interval
(year)
|
24-hour Rainfall Total
(inches)
| |
---|---|---|
1
|
2.02
| |
2
|
2.41
| |
10
|
3.38
| |
25
|
4.00
| |
50
|
4.50
| |
100
|
5.03
|
Time of concentration = Tc = [(Tlag/.6) * 60] (minutes)
|
Where:
| ||||
Tlag
|
=
|
lag time (hours)
| ||
L
|
=
|
hydraulic length of watershed (feet)
| ||
Y
|
=
|
average overland slope of watershed (percent)
| ||
S
|
=
|
maximum retention in watershed as defined by: S = [(1000/CN)
— 10]
| ||
CN
|
=
|
NRCS curve number for watershed
|