Return Interval
(year)
|
24-hour Rainfall Total
(inches)
| |
---|---|---|
1
|
2.40
| |
2
|
2.90
| |
10
|
4.36
| |
25
|
5.43
| |
50
|
6.38
| |
100
|
7.48
|
Time of Concentration = Tc = [(Tlag/0.6)
* 60] (minutes)
|
Tlag = L0.8(S+1)0.71900Y
|
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 as defined by the NRCS Loss
Method
|