HYDROLOGY OF NEfW YORK 



829 



found in 1824, on the same reach of canal as was measured by 

 Mr Childs in 1841, a total loss of from 1.68 to 1.75 cubic feet per 

 second per mile. It may be assumed that the springs and 

 streams allowed for by Mr Childs were delivering into the canal 

 in 1824 the same as in 1841, at least 0.17 to 0.25 cubic foot per 

 second per mile. We have, then, as the total supply in 1824 

 from 1.92 to 2.00 cubic feet per second per mile. Adopting the 

 latter figure as a maximum to compare with Mr Childs's figure 

 of 1.42 cubic feet per second per mile, as found in 1841, the con- 

 clusion is reached that the decrease in the loss by filtration — due 

 presumably to the gradual silting up of the bottom — is some- 

 thing like 0.58 cubic foot per second per mile. 



This conclusion could be applied to the conditions of the Erie 

 canal improvement of 1895 in which it was proposed to excavate 

 one foot from the bottom of many of the levels. The effect of this 

 would be to remove the silt accumulations of many years, thus 

 placing the bottom of the canal, as regards porousness and conse- 

 quent percolation and filtration loss, in the same condition as 

 when first constructed. This consideration alone indicated the 

 necessity of making the water supply of the enlarged canal 

 liberal in order to answ r er the demands of the first few years 

 while the bottom was again attaining a fixed condition. 



The experience of over eighty years in the operation of the 

 New York State canals has thoroughly shown the futility of any 

 attempt at excessive economy in water supply. In the absence 

 of systematic information as to yield of streams, the general 

 tendency has been to overrate the summer flow, with the result of 

 shortage frequently at points where the supply was believed to be 

 ample. The chief sources of such shortage may be enumerated 

 as follows : 



1) The great variation in the yield of catchment areas from 

 year to year, by reason of differences in the rainfall, humidity, 

 and temperature. 



2) The cutting off of forests, which has increased somewhat 

 the spring-flood flows and decreased the summer flow. 



3) The systematic drainage of large areas, which has also 

 tended to increase the flood flows and decrease the summer flows. 



