LAND DRAINAGE BY MEANS OF PUMPS. 51 
Tables 13 and 14 do not take into account the fixed charges, 
which include interest, depreciation, taxes, and insurance. In 
computing the fixed charges interest has been assumed at 6 per cent, 
taxes and insurance at 1 per cent, and depreciation at 6 per cent. 
While the rate of depreciation on the machinery might be somewhat 
greater than this, the cost of the machinery is only a part of the total 
cost of the plant, and a rate of 6 per cent is higher than would 
apply to the building, and especially to the foundation, the cost of 
which last item is often a large part of the cost of the completed 
plant. Tables 15 and 16 give the total cost per acre per year for 
the districts given. As before, two tables are made, one for steam 
and one for electrically driven pumps. 
*It will be noted that the average yearly cost per acre of total drain- 
age area is, for steam-driven plants, $0.78, and that the variation in 
cost is from a minimum of $0.40 for the Des Moines County District 
No. 1 plant to a maximum of $1.22 for the Lacey plant. Where 
the pumps are driven by motors the average yearly cost per acre 
of drainage area is $1.38, with a maximum of $1.89 for the East 
Peoria District and a minimum of $0.89 for the Big Swan District. 
As stated above, the amount of water pumped and other local condi- 
tions tend to alter the true relation between the costs of operation 
of the various plants. However, from three districts accurate and 
detailed records were obtained, so that the cost in operating expense 
of lifting an acre-foot of water 1 foot could be accurately determined. 
Table 17 is a statement of amount pumped and the unit cost on 
these three districts. 
Both plants on the Illinois River have a much nigher mean lift 
than has the one on the Mississippi River. A large variation in 
costs is noted for the different years for the Louisa-Des Moines plant. 
This can be traced directly to the average lift; the pumps do not 
work so efficiently at the lower lift. In this respect the plants on 
the Illinois River have a considerable advantage over the Louisa- 
Des Moines plant, as their lifts are higher and the pump efficiencies 
must be much better. In the early part of the discussion in this 
section it was assumed that under normal conditions the average 
amount of water to be removed per year was a depth of 15.2 inches. 
With the unit' costs as taken from the actual operating expenses of 
the three plants given in Table 17, the costs of drainage per acre 
per year have been calculated and are shown in Table 18. In select- 
ing the unit cost to use for the Louisa-Des Moines plant, the one 
corresponding to the highest head is taken, so that a better compari- 
son can be made with the plants on the Illinois River. However, 
the lifts are much higher for the latter plants, thus putting them at a 
considerable advantage; for if their lifts were as low as that of the 
Louisa-Des Moines plant their efficiencies would be much decreased 
