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NEW YORK STATE MUSEUM 



The catchment area of Hemlock lake is, as stated, 27,554 acres, 

 and the area of the lake itself at the elevation rhO.O is 1828 acres; 

 hence the lake surface is 6.6 per cent of the total catchment area, 

 or the catchment area is 15.1 times the area of the lake surface. 

 On this basis 1 inch on the whole area is 15.1 inches on the lake. 

 Taking into account these statements, it is clear that the data 

 of the table give approximately the natural runoff, although for 

 exact figures corrections for actual elevations of lake surface at 

 theibeginning, as well as at the end of each year, should be applied. 

 On this point see the discussion on tiie minimum flow of Hemlock 

 lake. 



Comparison of the runoff of Hemlock lake with that of the 

 river Thames in England. Hemlock lake may be compared with 

 the river Thames in England, where somewhat similar climatic 

 conditions obtain. The catchment area of the Thames above the 

 point of gaging is 3789 square miles, while the catchment area of 

 Hemlock lake is given at 43.1 square miles. It is shown on a 

 preceding page that comparison may be legitimately made be- 

 tween streams with even as great variation in catchment areas 

 as here exists. Accurate gagings are at hand of the Thames from 

 1883-1891, inclusive, from which it appears that the mean or 

 average rainfall during this period Avas 27.01 inches, and the mean 

 or average runoff, 8.49 inches, or the runoff was 31 per cent of 

 the rainfall. In order to compare the climate of the catchment 

 of the Thames with that of Hemlock lake we may consider the 

 following; 



The mean annual rainfall at Hemlock lake for the water years 

 1877-1900, inclusive, was 27.70 inches; the mean annual tempera- 

 ture for the same years was 50° Fahr., and the mean annual 

 evaporation for the years 1896 to 1903, at Mount Hope reser- 

 voir, 28 miles north of Hemlock lake, was 34.55 inches. The rain- 

 fall of Hemlock lake exceeds that of the Thames by only 0.6f> 

 inch. 



The mean evaporation from a water surface at Oxford, Eng- 

 land, for five years, 1852-1856, inclusive, was 31.01 inches; the 



