Rainfall Frequency in the Southeastern Wisconsin Region
SEWRPC Technical Report No. 40, Rainfall Frequency in the Southeastern Wisconsin Region, April 2000, presents the most current rainfall depth-duration-frequency information for the seven-county Southeastern Wisconsin Region. The data are recommended by the Commission staff for use in stormwater management applications. Moreover, the data are accepted by the Milwaukee Metropolitan Sewerage District (MMSD) for use in projects regulated under the MMSD Chapter 13 Rule, “Surface Water and Storm Water.” On July 22, 2005, the revised temporal rainfall distribution set forth below was approved by the Wisconsin Department of Natural Resources for use in floodplain zoning and Federal flood insurance applications throughout the State of Wisconsin.
The temporal rainfall distribution that was provisionally recommended in Technical Report No. 40 has now been replaced with the distribution set forth in Table 2 and Figure 1 below. That distribution is recommended to be applied with the SEWRPC 2000 rainfall depths for design and planning purposes.
A summary of the data is presented below, and a printed copy of Technical Report No. 40 is available on our Publication page.
Table 1
RECOMMENDED DESIGN RAINFALL DEPTHS
FOR THE SOUTHEASTERN WISCONSIN REGION
|
Recurrence Interval and Depths (inches)
|
|
Storm Duration
|
2 Yearsa
|
5 Yearsa
|
10 Yearsa
|
25 Years
|
50 Years
|
100 Years
|
|
5 Minutes
|
0.40
|
0.48
|
0.54
|
0.62
|
0.68
|
0.74
|
|
10 Minutes
|
0.64
|
0.76
|
0.85
|
0.98
|
1.08
|
1.19
|
|
15 Minutes
|
0.83
|
0.98
|
1.07
|
1.21
|
1.31
|
1.41
|
|
30 Minutes
|
1.07
|
1.29
|
1.45
|
1.68
|
1.85
|
2.02
|
|
60 Minutes
|
1.31
|
1.60
|
1.84
|
2.20
|
2.50
|
2.82
|
|
2 Hours
|
1.54
|
1.93
|
2.23
|
2.73
|
3.16
|
3.64
|
|
3 Hours
|
1.68
|
2.07
|
2.40
|
2.93
|
3.39
|
3.89
|
|
6 Hours
|
1.95
|
2.40
|
2.79
|
3.44
|
4.03
|
4.70
|
|
12 Hours
|
2.24
|
2.74
|
3.17
|
3.89
|
4.53
|
5.25
|
|
24 Hours
|
2.57
|
3.14
|
3.62
|
4.41
|
5.11
|
5.88
|
|
48 Hours
|
3.04
|
3.71
|
4.20
|
4.94
|
5.53
|
6.13
|
|
72 Hours
|
3.29
|
3.94
|
4.40
|
5.09
|
5.63
|
6.17
|
|
5 Days
|
3.77
|
4.42
|
4.84
|
5.43
|
5.86
|
6.26
|
|
10 Days
|
4.68
|
5.42
|
5.89
|
6.55
|
7.03
|
7.46
|
aFactors presented in U.S. Weather Bureau TP-40 were applied to the SEWRPC 2000 annual series depths with recurrence intervals of two, five, and 10 years, converting those depths to the partial duration series amounts set forth in this table. The annual series depths were adjusted as follows:
Two-year: multiplied by 1.136; five-year: multiplied by 1.042; and 10-year multiplied by 1.010.
Source: Rodgers and Potter and SEWRPC.
Table 2
SEWRPC RECOMMENDED RAINFALL DISTRIBUTION
|
Percent
of Total Storm Time
|
Cumulative Percent of
Total Storm Rain
|
|
0
|
0.0
|
|
5
|
2.7
|
|
10
|
4.8
|
|
15
|
6.9
|
|
20
|
9.5
|
|
25
|
13.2
|
|
30
|
18.9
|
|
35
|
28.5
|
|
40
|
42.2
|
|
45
|
56.6
|
|
50
|
68.4
|
|
55
|
76.5
|
|
60
|
81.6
|
|
65
|
85.2
|
|
70
|
88.0
|
|
75
|
90.3
|
|
80
|
92.2
|
|
85
|
94.0
|
|
90
|
95.8
|
|
95
|
97.7
|
|
100
|
100.0
|
Source: SEWRPC
Selections from Technical Report 40
Figure 32, Point Rainfall Intensity—Duration—Frequency Curves for Milwaukee,Wisconsin
Map 1, Rainfall Pattern Over Southeastern Wisconsin 24-Hour Period on August 6, 1986
Map 2, Rainfall Pattern Over Southeastern Wisconsin 26-Hour Storm on June 20-21, 1997
Map 3, Rainfall Pattern Over Southeastern Wisconsin 24-Hour Period on August 6, 1998
SEWRPC is collaborating with the Wisconsin Departments of Natural Resources and Transportation to provide funding for the Wisconsin portion of a National Weather Service project to update precipitation frequency information in the Midwestern states (Colorado, Iowa, Kansas, Michigan, Minnesota, Missouri, Nebraska, North Dakota, South Dakota, and Wisconsin). This study includes development of regional information within the states, and when it is completed in mid-2012, it is anticipated that it will become the standard for the Southeastern Wisconsin Region, replacing SEWRPC Technical Report No. 40.