278 
Journal of Agricultural Research 
V«l. XI, No. 6 
ment has been outlined by Okey. 1 It is believed that, in general, after 
a capacity of about 0.50 inch of water over the area drained has been 
provided in the main reservoir channels between the surface and a 
level 5 feet below it will be cheaper to obtain increased capacity to 
handle storms by enlarging the pumping plant rather than the reservoir. 
This will depend, however, on local costs for excavation and pumping 
machinery. 
TablS XII .—Average yearly number of storms of given intensities , based on daily rain¬ 
fall records of the United States Weather Bureau for New Orleans , La., 1871 to 1915, 
inclusive 
Average number of storms per year. 
Total 
rain¬ 
fall. 
1-day period. 
2-day period. 
3-day period. 
4-day period. 
5-day period. 
] 
6-day period, j 
1 
7-day period. 
| 
& 
t 
9-day period. 
1 
& 
1 
M 
; 11-day period. 
I 
1 
H 
13-day period. 
14-day period. 
15-day period. 
Inches. 
3. 
1.622 
0.688 
•333 
. 200 
.156 
. in 
.022 
3*020 
1*358 
.644 
•333 
.222 
.156 
.066 
4.060 
x. 869 
.866 
.466 
.311 
.156 
.089 
.044 
.022 
4. 
2.220 
1.043 
.644 
*356 
. 222 
. Ill 
.066 
*044 
5. 
!. 
6. 
•778 
.400 
. 289 
• 156 
. in 
.066 
•044 
0.866 
.489 
. 289 
. 200 
.156 
.066 
.066 
.022 
.022 
.022 
7. 
0.600 
•333 
.200 
. 200 
.089 
.089 
.044 
.022 
.022 
8 . 
0.378 
•245 
.200 
.133 
.089 
.044 
.022 
.022 
9. 
0.311 
•245 
•133 
.089 
.044 
.022 
.022 
10. 
0.267 
.178 
.089 
.044 
• 022 
.022 
11. 
0.200 
.089 
.044 
.022 
.022 
12. 
0. izi 
•444 
.022 
.022 
13. 
0.089 
.066 
.014 
14. 
0.066 
.044 
15. 
0.044 
In determining the proper combined capacity of the pumping plant 
and reservoir the main factor to be considered is the amount of rainfall 
in an assumed period for which provision is to be made. Examinations 
of the daily rainfall records of the United States Weather Bureau at 
New Orleans from 1871 to 1915 have been made, and the results are 
shown in Table XII. As the accompanying curves were prepared with 
data from storms which occurred when the land was wet, a determina¬ 
tion has been made of the proportion of storms which occur when the 
land is wet. Of all the storms of over 2 inches in 24 hours which have 
occurred on the districts during the time covered by the records, 64 per 
cent occurred on a wet and 36 per cent on a dry surface; of all storms 
over 4 inches the percentages are 54 per cent and 46 per cent, respec¬ 
tively. Of course the storage capacity of the land influences the run-off 
from the small storms relatively much more than it does that from the 
large ones. However, an examination of the daily rainfall and pumping 
records will show that heavy rains on a dry soil do not make very heavy 
demand on the pumping plant. It is believed, therefore, that a reduc- 
1 Okey, C. W. THE WET LANDS OV SOUTHERN LOUISIANA AND THEIR DRAINAGE. U. S. Dept. Agr. 
Bui. 71. P- 71 - 75 - 1914- 
