ETL 1110-2-537
31 Oct 97
within the range of values defined by Yl and Ym is
Table 3
determined by the values in Table 4.
Plotting Positions Estimated from Stage-Frequency
Curve
Years of Record
Stage
Table 2
Example Stage-Frequency Curve
1
7.27
0.9524
Event Order
Stage
Exceedance Frequency
2
8.45
0.9048
1
6.60
0.9900
3
9.10
0.8571
2
6.80
0.9600
4
10.80
0.8095
3
7.40
0.9500
5
12.33
0.7619
4
7.95
0.9250
6
13.53
0.7143
5
8.55
0.9000
7
14.73
0.6667
6
8.95
0.8600
8
15.52
0.6190
7
9.95
0.8400
9
16.32
0.5714
8
11.05
0.8000
10
17.07
0.5238
9
12.70
0.7500
11
17.80
0.4762
10
13.85
0.7000
12
18.53
0.4286
11
14.90
0.6600
13
19.20
0.3810
12
15.80
0.6000
14
19.90
0.3333
13
16.70
0.5500
15
20.52
0.2857
14
17.40
0.5000
16
21.29
0.2381
15
18.25
0.4500
17
22.11
0.1905
16
18.90
0.4000
18
23.00
0.1429
17
19.70
0.3500
19
24.13
0.0952
18
20.30
0.3000
20
25.80
0.0476
19
21.10
0.2500
(4) Step 4: Calculation of nm and nl is performed
20
21.95
0.2000
using Equations 8 and 9. Application of the equations
21
24.00
0.1000
22
25.70
0.0500
function be obtained at each point as the inverse of the
23
27.40
0.0200
slope of the nonexceedance frequency curve. From
24
27.60
0.0180
Table 4, the data are obtained to take a centered differ-
25
27.80
0.0160
ence approximation to this slope. The inverse slope at
Ym = 21.29 is
26
28.00
0.0140
27
28.20
0.0120
28
28.40
0.0100
0.810 & 0.714
fY ( Yl ) -
(12)
' 0.035
29
28.90
0.0050
13.53 & 10.80
30
29.10
0.0025
Note: Frequency curve integral moments:
mean = 17.00 ft, std dev = 5.60 ft.
8