32 
BULLETIN 304, U. S. DEPARTMENT OF AGRICULTURE. 
In each of Tables 8, 9, and 10 the maximum for each month is 
shown by heavy-faced figures, as is also the yearly maximum. It 
will be noted that the greatest mean monthly rainfall is in June in 
two cases and in July in the other, thus showing that the maximum 
rainfall is to be expected during the months when farming operations 
are at their height. The mean annual precipitation for the three 
stations is 37.39 inches. A study of the tables has shown that a 
monthly rainfall of 6 inches occurs a little oftener than once each 
year. A monthly rainfall of 8 inches occurs once in 3.5 years, and 
one of 10 inches once in 11 years. A rainfall of 15 inches during a 
period of two successive months occurs once in 3.6 years. It would 
appear from these figures that a pumping plant should be able to 
handle a monthly rainfall of at least 8 inches. 
Table 11 shows the average number of storms per year, of the given 
intensities, for short periods of from 1 to 10 days, that may be 
expected in the section under consideration. This table was obtained 
from a study of the daily precipitation records of Muscatine, Peoria, 
and St. Louis. 
A study of the rainfall records of Muscatine, Peoria, and St. Louis 
shows that about two-thirds of the storms of the various intensities 
given in Table 11 occurred from April to September, inclusive, the 
months during which crops are most injured by occasional flooding. 
During the six months from October to March, inclusive, occasional 
flooding of the land would do little if any damage in the section under 
consideration. Therefore the storms occurring during the winter 
months may be disregarded in the determination of the proper 
capacity of pumping plant. This can be done by reducing the 
number of storms of each given intensity by one-third. For instance, 
Table 11 shows that on the average a storm of 2 inches in two days 
occurs three times a year. Only two of these storms occur at a time 
of the year when damage to crops would be caused by flooding. 
Table 11. — Average yearly number oj storm periods oj jrom 1 to 10 days' duration. 
[Based upon daily precipitation records of the United States Weather Bureau for Muscatine, Iowa, 1S54- 
1914; Peoria, 111., 1856-1914; and St. Louis, Mo., 1843-1914.] 
Average number of storms per year. 
Total rainfall. 
1-day 
period. 
2-day 
period. 
3-day 
period. 
4-day 
period. 
5-day 
period. 
6-day 
period. 
7-day 
period. 
8-day 
period. 
9-day 
period. 
10-day 
period. 
2.018 
.479 
.172 
.041 
.012 
3.059 
.900 
.320 
.083 
.024 
.006 
3.615 
1.172 
.438 
.142 
.041 
.012 
4.071 
1.456 
.545 
.160 
.047 
.018 
1.580 
.651 
.195 
.071 
.030 
.006 
1.722 
.775 
.290 
.077 
.047 
.006 
.006 
0.847 
.355 
.100 
.053 
.012 
.012 
0.912 
.444 
.118 
.059 
.024 
.018 
.006 
0.479 
.165 
.071 
.024 
.018 
.006 
0.520 
.207 
.077 
.030 
.018 
.006 
