Factor
|
Swale Bends
(degrees)
| |
---|---|---|
1.75
|
30 to 60
| |
2.00
|
60 to 90
| |
2.50
|
90 or greater
|
Return Interval
(year)
|
24-hour Rainfall Total
(inches)
| |
---|---|---|
1
|
2.35
| |
2
|
2.82
| |
10
|
4.09
| |
25
|
5.05
| |
50
|
5.94
| |
100
|
6.99
|
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 = [(1000/CN)
— 10]
| ||
CN
|
=
|
NRCS curve number for watershed
|