22 BULLETIN 304, U. S. DEPARTMENT OF AGRICULTURE. 
vent danger to the lower portions from the run-off from the higher 
areas. Where drainage from higher land flows into the district a 
larger run-off coefficient must be used for the higher area. The 
proper amount depends upon the nature of the country. For rolling 
pasture land free from undergrowth, or for cultivated corn land, 
probably an increase of 50 per cent in the coefficient, or a total of 
three-eighths inch, for such upland areas is none boo great. Where 
feasible, the drainage from such higher areas should be diverted 
around the district, as previously explained, instead of being brought 
to the pumping plant. 
With a considerable reservoir storage area within the district, the 
size of the pumping plant may be materially reduced. If the stor- 
age area equals 5 per cent of the total area, a 2-inch rainfall, all run- 
ning into the reservoir, would raise its level only 40 inches. There- 
fore, if a rise of 3 feet in the reservoir can be permitted it would 
seem that the capacity of the pumping plant could certainly be re- 
duced by one-third and possibly by one-half of what would otherwise 
be required. 
If tile drainage at a depth of 3 feet or more is extensively used, the 
demand upon the pumping plant will be somewhat reduced, for the 
tiled land will act like a reservoir in storing a large amount of water 
and will deliver it only slowly to the ditches. On the other hand, an 
extensive system of shallow open field ditches will deliver the rainfall 
rapidly and may thus damage any especially low areas unless the 
capacity of the pumping plant is increased. If the levees have been 
properly constructed, the amount of seepage through them can never 
be sufficient to affect the pumping plant. Cases have been known, 
however, of levees so poorly built that the quantity of water coming 
through them was sufficient not only to endanger the stability and 
safety of the levees themselves, but also to increase appreciably the 
amount of water to be pumped. 
If the soil is very stiff and tenacious the surface run-off after a 
heavy summer shower will be greater than from a porous open soil. 
During a time of flood in the river, a sandy subsoil may develop 
springs and boils, not only in the bottoms of the ditches, but some- 
times even in the fields. The quantity of water that may be received 
in this way is very uncertain, but it is not probable that it is often 
sufficient in amount to affect the pumping plant. 
A pumping plant that is designed to operate night and day may, 
of course, be smaller than one intended to operate only in the day- 
time. Practically all plants are expected to run nights occasionally, 
when needed. Pumping plants are operated chiefly during the 
months from March to June. One of the times of longest continuous 
operation during the whole year is always at the beginning of pump- 
ing in the spring, because if there has been no pumping during the 
