28 



BULLETIN 304, U. S. DEPARTMENT OF AGRICULTURE. 



and a pumping plant equipped with two 50-inch pumps having a com- 

 bined capacity of 225 cubic feet per second, or a depth of 0.33 inch 

 on the entire watershed per 24 hours Accurate daily records were 

 available for the years 1912 and 1913. The elevation of the land in 

 this district with reference to the usual stages in the Mississippi River 

 is such that for several months in each year gravity drainage is possi- 

 ble through sluice gates. The gates are usually open during the sum- 

 mer, when the storms of the greatest intensity and amount are likely 

 to occur. Under the conditions that usually prevail the time of 

 greatest pumping is during the spring months. The Mississippi and 

 Iowa Rivers, which bound the district on two sides, are usually 

 high at that time, while seepage is at the maximum and evaporation 

 is near the minimum. When pumping was started in March, 1912, 

 there was considerable snow and ice in the district; the rivers rose 

 very nearly to the top of the levees, causing heavy seepage. The 

 rainfall was about normal. Table 6 shows the daily rainfall and run- 

 off for March and April, 1912; it is unlikely that the run-off from this 

 district will much exceed these figures at any time. 



Table 6- 



-Daily rainjall and run-off, 



Louisa-Des Moines Drainage District No 



4, 1912. 



Day. 



Rainfall. 



Run-off. 



Day. 



Rainfall. 



Runoff. 



Day. 



Rainfall. 



Run-off. 



Mar. 26 



Inches. 

 0.84 



Inches. 

 0.18 

 .21 

 .21 

 .21 

 .23 

 .23 

 .22 

 .21 

 .21 

 .22 

 .22 

 .22 

 .23 

 .23 

 .24 

 .24 

 .24 

 .25 



Apr. 13 



Inches. 



Inches. 

 0.26 

 .25 

 .25 

 .24 

 .19 

 .24 

 .26 

 .17 

 .19 

 .25 

 .25 

 .18 

 .17 

 .17 

 .18 

 .17 

 .17 

 .16 



May 1 



2 



Inches. 

 1.86 



Inches. 

 0.16 



27 



14 





.16 



28 





15 





3 





.17 



29 .. 



16 





4 





.18 



30 





17 



18 



1.93 



5 





.16 



31 





6 





.17 







19 





7 





.15 



2... 





20 





8 





.15 



3. . 





21 





9 





.15 



4 





22 





10 





.13 



5... 





23 





11 





.13 



6. . 



.20 



24 





12 



13 



.27 



.12 



7 



25 





.13 



8. . . . . 





26 





14 





.13 



9... 





27 





15... 





.00 



10... 





28 





16 



17 



.46 



.12 



11 





29 





.13 



12 



.60 



30 





18 





.11 















The plant was not operated an entire day, i. e., 24 consecutive 

 hours, during this time. The object was not to remove all the water 

 possible in one day, but to hold the stage of water in the internal 

 drainage channels below the danger point. If the plant had been 

 operated at full capacity for several entire days, it would have meant 

 the skipping of a day to allow sufficient water to collect for pumping. 

 The mean lift would also have been increased. In this case, con- 

 trary to the usual condition on pumping districts, the amount pumped 

 each day must very closely approximate the amount of water that 

 actually ran into the main drainage channels on that day. A study 

 of the stage of water in the main ditch bears out this conclusion. 

 During the pumping season of 1913 neither heavy precipitation nor 

 high river stages occurred and the amount pumped was never more 

 than 0.16 inch in any one day. In Table 7 are given the monthly 

 totals of rainfall and amounts pumped. 



