Return Interval
(years)
|
24-Hour Rainfall Total
(inches)
| |
---|---|---|
1
|
1.99
| |
2
|
2.38
| |
10
|
3.35
| |
25
|
3.96
| |
50
|
4.46
| |
100
|
4.99
|
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
|