juiy^o, I9I7 Evaporation from Water and River-Bed Materials 257 



Table XXV. — Variation of evaporation loss from stream-bed materials, with size of 

 sand grain — Water plane from j to 24 inches below the surface. {See fig. ii) 



o Interpolated from figure 11. AU other percentages are from Tables XIX to XXIII. 



The evaporation percentages given include all the observed points 

 shown in figure ii. Points interpolated from figure ii are indicated. 

 From this table figure 12 has been plotted. Observed figures are 

 distinguished from the interpolated ones mentioned by the method 

 of plotting. 



Figure 13 shows the percentage of moisture in the top 4 inches of 

 Laboratory soil with the water table at different depths. The upper 

 curve, over the range of materials with 60 per cent size from 0.003 

 to 0.057 inch, indicates that with water 3 inches below the sand 

 surface the loss by evaporation from this surface is from 89 to 66 

 per cent of that from a water surface of the same size and under 

 the same external conditions. The graph shows these evaporation 

 values for depths of water table from 3 to 24 inches, at 12 inches 

 the range or loss being from 79 to 24 per cent, the greater loss in each 

 case occurring from material of fine grain or texture. 



Table XXVI. — Factors for estimating evaporation losses from the surfaces of siream,-bed 



materials 



[Multiply the evaporation from a water surface of the same size and similarly exposed by the factors given 

 to get the evaporation from the sand surface] 



One check upon this work has been found; in 191 5 Diesem at North 

 Platte found that the evaporation loss with water level 3 inches below 

 the sand surface, from material from the South Platte River taken 

 98976°— 17 4 



