Return Interval
(year)
|
24-Hour Rainfall Total
(inches)
|
---|---|
1
|
2.06
|
2
|
2.46
|
10
|
3.46
|
25
|
4.11
|
50
|
4.64
|
100
|
5.21
|
Time of Concentration = Tc = [(Tlag/0.6) * 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
|