36

equipped with a 6,000,000-gallon pump and a 300-kilowatt synchronous motor, which cost $29,380. The filtering galleries and connections cost, in round numbers, $21,000.

No better idea can be given of the operation of the plant than to append a report for the twelve months ending November 30, 1899:

For the purpose of comparison, the receipts and expenditures for the last three years are here tabulated:

SILTING UP OF LAKE MCDONALD.

In 1890 cross sections of Colorado River were taken at sixteen stations, as shown in the tabular statement on page 38 and in fig. 6. The complete outline of the diagrams in fig. 6 represents the original cross section, the horizontal line being the water surface even with the crest of the dam and the shaded area showing the amount of silt that had been deposited up to February, 1900. All vertical dimensions are exaggerated three times over the horizontal dimensions. Cross sections were again taken for the United States Geological Survey in May, 1897, also in January, 1900. The silt deposited from 1893 to 1897 is represented by the lower shaded area, and that deposited from 1897 to 1900 by the upper shaded area.

The water first flowed over the crest of the dam on May 16, 1893, at which time there were 83,556,000 cubic yards of water in the main channel of the lake up to the level of the crest of the dam; in 1897 there were only 51,889,000 cubic yards of water in the channel, the remaining 31,667,000 cubic yards (or 38 per cent of the original capacity)