LA1STD DRAINAGE BY MEAN'S 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 

 gFeater 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- 

 Dcs 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 lift- are much higher for the Latter plants, thus putting them at a 

 considerable advantage; for it' their lifts were as low as that of the 

 Louisa-Des Moines plant their efficiencies would be much decreased 



