512 REPORT OF THE COMMISSIONERS OF 



inches per year, this difference representing approximately the difference in the State 

 of New York between a forested and deforested area. In considering the significance 

 of this tentative conclusion we should bear in mind that the Upper Genesee area is 

 practically bare of forest. 



The data of the Croton River may also be referred to. For this stream I have 

 tabulated the rainfall, run-off, evaporation and temperature for a period of 27 years, 

 from 1870 to 1896, inclusive. The data of such tabulation, as derived from the 

 records of the Croton Water Department, have been properly corrected for the storage 

 of the several reservoirs on that area, so that the figures given in the table represent 

 the true run-off of the stream. The average annual rainfall of the Croton area may 

 be taken at 48.40 inches, and the average run-off of the river for 25 years at 24.6 

 inches, the difference of the two, representing the evaporation, amounting to 23.8 

 inches. In 1883, with a rainfall of 43.15 inches, the evaporation amounted to 27.2 

 inches. In 1888, with a rainfall of 63.6 inches, the evaporation amounted to 25.7 

 inches, but in 1880, with a rainfall of only 38.50 inches, the evaporation still amounted 

 to 23.20 inches. Speaking generally we may say, therefore, that the evaporation of 

 the Croton area is persistent at about 24 inches per year, which demand must be 

 satisfied so long as the area remains in the present condition and before there is much 

 surplus water to appear as run-off. The area of the watershed above the point of 

 gauging is 338 .square miles, and the percentage of timber area does not exceed about 

 25 per cent. A considerable portion of this is wild land covered with such scant 

 forest growth and brush as to afford very little protection. Hence we may say that 

 such forest growth on the Croton area as has value in conserving stream flow probably 

 does not much e.xceed about 20 per cent. There is, however, between 2 and 3 per 

 cent, of storage on reservoir surfaces which has some effect on the aggregate run-off. 

 Generally the Croton area is hilly, with the rock mainly gneissic, overlaid with drift 

 and gravel frequently to considerable depth. There are also some swamps. 



As another interesting stream in the Iiastern United States we may mention the 

 Muskingum River, in Ohio, of which records are available from 1888 to 1896, 

 inclusive. This stream mostly issues from the flat areas of Central (3hio where there 

 is very little timber, and shows such lower run-offs as may be expected from that kind 

 of an area. In 1888, with a rainfall of 42.60 inches, the evaporation amounted to 

 32.28 inches. The run-off for that year was 10.32 inches. In 1889, the rainfall was 

 35.88 inches, the run-off 8.22 inches, and the evaporation 27.66 inches. In 1890, the 

 rainfall was 46.97 inches, the run-off 26.84 inches, and the evaporation 20.13 inches. 

 In 1892, the rainfall was 41.74 inches, run-off 13.38 inches, and evaporation 28.36 

 inches. In 1893, the rainfall was 42.36 inches, run-off 16.20 inches, evaporation 26.16 

 inches. In 1894, the rainfall was 30.51 inches, the run-off 8.70 inches, and the 



