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Lake County Unincorporated
City Zoning Code

APPENDIX K

RAINFALL TABLES

   Rainfall Depth-Duration Frequency Tables for Lake County
   Rainfall is in inches
Storm Duration
2- month
3- month
4- month
6- month
9- month
1- year
2- year
5- year
10- year
25- year
50- year
100- year
500- year
Storm Duration
2- month
3- month
4- month
6- month
9- month
1- year
2- year
5- year
10- year
25- year
50- year
100- year
500- year
5 minutes
0.19
0.22
0.24
0.27
0.31
0.33
0.40
0.52
0.62
0.77
0.90
1.03
1.35
10 minutes
0.33
0.38
0.41
0.47
0.53
0.58
0.70
0.90
1.08
1.35
1.58
1.80
2.36
15 minutes
0.42
0.49
0.53
0.61
0.69
0.75
0.90
1.16
1.39
1.74
2.03
2.32
3.04
30 minutes
0.58
0.66
0.73
0.83
0.94
1.03
1.24
1.59
1.91
2.39
2.78
3.17
4.16
1 hour
0.74
0.84
0.93
1.05
1.20
1.30
1.57
2.02
2.42
3.03
3.53
4.03
5.28
2 hours
0.91
1.04
1.14
1.30
1.48
1.61
1.94
2.49
2.99
3.74
4.35
4.97
6.52
3 hours
1.00
1.15
1.26
1.44
1.63
1.77
2.14
2.75
3.30
4.13
4.80
5.49
7.20
6 hours
1.18
1.35
1.48
1.68
1.91
2.08
2.51
3.23
3.86
4.84
5.63
6.43
8.43
12 hours
1.37
1.56
1.71
1.95
2.21
2.41
2.91
3.74
4.48
5.61
6.53
7.46
9.78
18 hours
1.48
1.69
1.85
2.11
2.39
2.61
3.14
4.04
4.84
6.06
7.05
8.06
10.57
24 hours
1.57
1.80
1.97
2.24
2.55
2.77
3.34
4.30
5.15
6.45
7.50
8.57
11.24
48 hours
1.72
1.97
2.16
2.46
2.79
3.04
3.66
4.71
5.62
6.99
8.13
9.28
12.10
72 hours
1.87
2.14
2.34
2.67
3.03
3.30
3.97
5.08
6.05
7.49
8.64
9.85
12.81
120 hours
2.08
2.38
2.61
2.97
3.37
3.67
4.42
5.63
6.68
8.16
9.39
10.66
13.81
240 hours
2.63
3.01
3.30
3.76
4.27
4.65
5.60
7.09
8.25
9.90
11.26
12.65
16.00
 
References:      ISWS Bulletin 75 Precipitation Frequency Study for Illinois
         James R. Angel and Momcilo Markus
         Illinois State Water Survey, March 2020
*Multiplication Factor - Average ratios of X-hour/24-hour rainfall for Illinois, 1989 Bulletin 70
**6 County - A multiplicative factor is not available for these storm events. Therefore, the 6-county Bulletin 70 data is used for regulatory studies.
HUFF RAINFALL DISTRIBUTIONS
The Huff quartiles represent the typical rainfall distribution for four different storm duration ranges. The First quartile applies to storms less than or equal to six hours long. Second is for storms greater than six hours and less than or equal to 12, while the third Huff quartile is for storms greater than 12 hours and less than or equal to 24 hours. Fourth quartile storms apply to storm durations greater than 24 hours.
 
Area < 10 SM
 
Area > 10 & Area < 50
 
Area > 50 & Area < 400
Portion of the Storm
First Quartile
Second Quartile
Third Quartile
Fourth Quartile
First Quartile
Second Quartile
Third Quartile
Fourth Quartile
First Quartile
Second Quartile
Third Quartile
Fourth Quartile
 
Area < 10 SM
 
Area > 10 & Area < 50
 
Area > 50 & Area < 400
Portion of the Storm
First Quartile
Second Quartile
Third Quartile
Fourth Quartile
First Quartile
Second Quartile
Third Quartile
Fourth Quartile
First Quartile
Second Quartile
Third Quartile
Fourth Quartile
0/24
0.00
0.00
0.00
0.00
 
0.00
0.00
0.00
0.00
 
0.00
0.00
0.00
0.00
1/24
8.36
2.29
2.05
2.31
 
6.41
1.48
1.33
1.48
 
4.59
0.88
0.72
0.90
2/24
17.73
4.82
4.31
4.79
 
15.69
3.57
3.02
3.34
 
13.49
2.38
1.85
2.29
3/24
28.11
7.78
6.67
7.12
 
27.45
6.39
5.13
5.72
 
25.94
4.93
3.47
4.36
4/24
38.33
11.33
9.12
9.78
 
38.91
10.02
7.53
8.56
 
39.17
8.52
5.57
7.10
5/24
47.45
15.79
11.71
12.53
 
49.34
14.71
10.01
11.69
 
51.04
13.19
8.28
9.93
6/24
55.50
21.39
14.36
15.23
 
58.55
20.89
12.65
14.19
 
60.79
19.59
10.96
12.84
7/24
62.25
28.41
16.91
17.91
 
65.88
28.91
15.24
17.19
 
69.26
27.46
13.79
15.46
8/24
67.22
36.44
19.64
20.33
 
71.10
37.55
18.17
19.69
 
74.80
37.17
16.35
17.83
9/24
70.82
45.29
22.78
22.83
 
74.92
46.86
21.46
22.27
 
78.74
47.77
19.66
20.12
10/24
74.17
54.35
26.33
25.41
 
78.30
56.25
25.36
24.81
 
82.20
58.18
23.46
23.12
11/24
76.97
62.38
30.93
28.35
 
81.16
64.84
29.90
27.46
 
85.13
67.64
28.07
25.76
12/24
79.81
69.76
36.35
31.25
 
83.75
72.90
35.60
30.33
 
87.38
75.86
34.06
28.26
13/24
82.55
75.48
43.92
33.90
 
86.20
79.07
43.42
32.42
 
89.58
82.04
42.30
30.99
14/24
85.18
80.38
52.11
36.33
 
88.64
83.97
52.18
34.28
 
91.45
86.92
52.02
33.68
15/24
87.40
84.70
61.02
38.61
 
90.81
87.58
61.88
36.89
 
93.35
90.33
62.76
36.12
16/24
89.47
87.81
69.89
41.24
 
92.58
90.67
71.81
39.73
 
94.80
93.09
72.80
39.07
17/24
91.17
90.22
78.19
45.08
 
93.99
92.76
80.43
43.85
 
95.99
94.82
82.27
42.93
18/24
92.70
92.17
84.92
51.29
 
95.19
94.59
87.25
49.87
 
96.94
96.25
89.19
48.98
19/24
94.03
93.81
89.74
59.31
 
96.35
95.97
92.01
58.93
 
97.70
97.34
93.60
59.22
20/24
95.36
95.29
93.11
69.19
 
97.27
97.10
95.04
69.85
 
98.35
98.21
96.33
71.66
21/24
96.56
96.57
95.34
80.05
 
98.03
97.99
96.90
82.36
 
98.86
98.83
97.97
85.18
22/24
97.74
97.74
97.06
89.71
 
98.74
98.72
98.22
92.59
 
99.28
99.30
98.98
94.64
23/24
98.85
98.84
98.56
96.04
 
99.37
99.39
99.21
97.96
 
99.66
99.67
99.58
98.77
24/24
100.00
100.00
100.00
100.00
 
100.00
100.00
100.00
100.00
 
100.00
100.00
100.00
100.00
 
References: Floyd A. Huff and James R. Angel, 1989 ‘Frequency Distributions and Hydroclimatic Characteristics of Heavy Rainstorms in Illinois’, Illinois State Water Survey, Bulletin 70.
(Ord., Appendix K, passed 10-13-2009; Ord. 22-1060, passed 8-9-2022; Ord. 23-1056, passed 8-8-2023)