FLOOD00005

• County: Statewide
• Title: Precipitation Records and Flood-Producing Storms in Cheyenne Wyoming
• Date: 10/23/2003
• Prepared For: Cheyenne
• Floodplain - Doc Type: Educational/Technical/Reference Information

Table 4.--Precipitation intensity for storms of selected recurrence

intervals and durations, using data available through 1986

Precipitation intensity, in inches per hour
Recurrence interval, in years
Duration 2 5 10 25 50 100
Gumbel distribution
5 minutes 3.48 4.92 5.88 7.20 8.04 9.00
10 minutes 2.58 3.72 4.44 5.40 6.06 6.78
15 minutes 2.20 3.13 3.76 4.52 5.12 5.68
30 minutes 1. 34 2.00 2.44 3.00 3.42 3.82
1 hour .79 1. 27 1.59 1. 99 2.28 2.58
2 hours .46 .78 1.00 1. 26 1.46 1. 66
24 hours .06 .09 .11 .13 .15 .17
Log-Gumbel distribution
5 minutes 3.23 4.67 6.15 8.49 10.70 13.78
10 minutes 2.44 3.62 4.77 6.58 8.47 10.92
15 minutes 2.00 2.97 3.82 5.39 6.79 8.75
30 minutes 1. 26 1. 91 2.46 3.48 4.48 5.77
1 hour .74 1. 12 1.48 2.09 2.75 3.55
2 hours .41 .62 .83 1.17 1. 51 1. 95
24 hours .05 .08 .10 .13 .16 .20
Log-Pearson Type III distribution
5 minutes 3.42 4.75 5.70 6.98 8.00 9.07
10 minutes 2.64 3.66 4.38 5.40 6.12 6.90
15 minutes 2.20 3.04 3.60 4.36 4.96 5.56
30 minutes 1.34 1. 96 2.42 3.06 3.56 4.12
1 hour .73 1.10 1. 41 1. 87 2.27 2.73
2 hours .41 .63 .83 1.16 1.46 1.84
24 hours .06 .08 .10 .13 .15 .18

Method of Analysis

Dimensionless hyetographs of cumulative precipitation versus time were
drawn for nine flood-producing storms that occurred between 1904 and 1973;
total precipitation for these storms ranged from 0.57 to 2.70 inches. The
hyetographs were based on the 5-minute incremental precipitation data of
Craig and Rankl (1978). In addition, a dimensionless hyetograph was drawn
for the storm of August I, 1985. Pattern index was calculated for each of
the storms by graphical methods. The August 1 storm was compared to the
other storms to determine whether it was anomalous.

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