HYDROLOGY OF NEW YORK 



791 



The table of evaporation from a water surface, as observed at 

 the Mount Hope reservoir of the Rochester Waterworks, shows 

 that for the navigation months, April to November inclusive, 

 evaporation ranges from 1.33 inches in November 1897, to 6.85 

 inches in July 1898. The water surface of the proposed summit 

 level is so small as to make evaporation, even in the maximum 

 month, hardly worth taking into account. At G.85 inches for the 

 month the evaporation on the summit level becomes, roundly, 5 

 cubic feet per second. In order to give evaporation some value in 

 the estimate of total water supply we will take it at from 5 to 10 

 cubic feet per second. 



There is no rational method of estimating percolation loss for a 

 canal under the conditions which exist in the Mohawk valley. The 

 drainage is all towards the valley, and at first thought it might 

 appear that percolation was a negligible quantity. However, if 

 we consider that the total water supply, as estimated for the 

 summit level, takes into account the entire yield of the catchment 

 area tributary to the main channel, and further consider that the 

 channel, as located, has its water surface for a considerable dis- 

 tance several feet above the ordinary water plane of the Mohawk 

 river and Wood creek in their natural condition, we may conclude 

 that percolation ought not to be entirely neglected, more specially 

 because the soils in the Mohawk bottom are open and porous, and 

 without some method of consolidation of the natural soils, which 

 does not now occur to the writer, can be devised, there is likely 

 to be considerable loss from percolation. By way of showing the 

 relation of water surface of the summit level to ordinary water 

 levels in the Mohawk river and Wood creek the following data are 

 cited : 



At a distance of 17,000 feet east of Rome the ordinary water 

 surface of the Mohawk river is at an elevation of 415, or the same 

 as water surface of the summit level ; 24,000 feet east of Rome it is 

 413 ; 32,000 feet east it is 408 ; 41,000 feet east, 404, and 47,000 feet 

 east, 401. 



At 17,500 feet west of Rome the ordinary water surface of Wood 

 creek is at 414, or one foot lower than the summit level ; at 21,500 

 feet west of Rome it is 408, and at 25,500 feet west, 398. 



The writer has no way of demonstrating the proposition, 

 although it seems clear enough to him that with an open, porous 

 soil the percolation from the canal at points where the summit 

 level is raised somewhat above the ordinary water level of the 

 Mohawk river and Wood creek will be considerable. The porous 

 soils of these valleys will take up water like a sponge, making 



