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 = ((1,000/CN)
- 10)
| |
CN
|
=
|
NRCS curve number for watershed
|