LAND DRAINAGE BY MEANS OF PUMPS. 21 
starting the pump is less quickly seen in the morning, but the lower- 
ing of the water is gradual throughout the day. After a few days of 
such operation the supply of water diminishes and the pumps are 
not run the whole day. 
Later, since it is troublesome to start up a big plant for only a few 
hours of operation, the speed of the engine and pump is reduced 
to diminish its discharge, or, if there is more than one pump in the 
plant, only one may be run. At last, days are skipped and pumping 
ceases entirely. After every rain of any importance, the pumps are 
started and a similar cycle of operations transpires, extending over 
a longer or shorter period, according to the amount of water to be 
removed. In some districts pumping for the season ends in June, and 
drainage is by gravity for the remainder of the summer. In others no 
gravity drainage is available, and the pumps must be run later in the 
season. Thus it is clear that, though the pumps must constantly be 
in readiness for use, their operation is very intermittent. The total 
time of running in a whole year never exceeds 60 to 90 days of 24 
hours each. In some seasons it is not more than 15 to 20 such days. 
The size of pumping plant required for any particular district 
depends upon a variety of conditions, among which are the size and 
slope of the drainage district and of any other area from which drain- 
age water is received; the amount of storage capacity available in 
ditches and reservoirs; the system of interior drains used and the 
method of construction adopted for the levee; the nature of the soil 
and subsoil; the method of operation of the pumping plant; the 
kind of crops raised and the degree of drainage required; and the 
amount and distribution of the rainfall throughout the year. 
In the vicinity of Illinois the weight to be given to some of these 
factors is very small, and in the present state of our knowledge no 
definite allowance can be made for them. Yet, notwithstanding our 
ignorance concerning some of them, it may be profitable to discuss 
briefly the nature of the effect of each. This is a field in which much 
careful study is still needed and must be carried out to secure the 
complete knowledge necessary for the most satisfactory design and 
management of the pumping machinery of drainage districts. 
Along the Illinois and upper Mississippi Rivers the majority of 
pumping plants already installed have been planned to have a 
maximum pumping capacity sufficient to remove in 24 hours one- 
fourth inch in depth of water over the entire district. This is 
equivalent to 6.74 cubic feet per second per square mile of drainage 
area, or 0.0105 cubic feet per second per acre. 
It is doubtful whether any change should be made in the one- 
quarter inch coefficient solely on account of change in the size of 
the district; however, where some portions of the district are mate- 
rially higher than others, the coefficient might be increased to pre- 
