Nov. 5, 1917 
Run-off from Drained Prairie Lands 
277 
each set of curves is shown the area of the district, the average capacity 
of the pumping plant per 24 hours, and the storage capacity of the 
main drainage channels between the surface and a level 5 feet below. 
From these separate curves composite curves have been drawn which 
represent the average run-off from all the districts (fig. 5). 
It is evident that the effect on the run-off of a change in the capacity 
of the pumping plant can not all be measured by the change of level 
of the water in the main reservoir channels, as greater slope and velocity 
Fig. 5.—Composite curves for eight districts, showing probable run-off for storm periods of from one to 
four days. 
of water occur in the drainage channels when a larger pumping plant 
is installed. This effect extends even to the small field ditches. 
In estimating the run-off likely to result from an assumed storm on 
a given district the curve used should be that for the district which 
resembles the given district in area, pumping-plant capacity, reservoir 
capacity, and general conditions. The curves may be considered only 
as representing general tendencies and not definite values. They should 
be of service, however, in making the proper adjustment between reser¬ 
voir and pumping-plant capacity, A method for making this adjust- 
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