66 



FORESTRY AND IRRIGATION 



February 



oration was found. At 120 feet the had open gaps in it and the nearest 



evaporation was 17 per cent, greater evaporometer was set up in the lee 



than at 20 feet. Three of the instru- of a clump of 6 trees spanning a 



ments were next set up at 20, 40 and length of 40 feet, there being a gap 



60 feet, and at 280, 300, and 320 feet of nearly equal length on either side, 



from the same grove and in the same To the windward of this hedge there 



field. During one hour the amounts was a naked field 80 rods wide re- 



of evaporation were as given in the cently plowed and being planted to 



next .table. 



EVAPORATION AT ONE FOOT ABOVE THE SURFACE AT 



20, 40, 60, AND AT 280, 300, AND 320 FEET TO 



THE LEEWARD OF A BLACK OAK GROVE IN A 



FIELD OF SANDY SOIL RECENTLY 



PLANTED TO CORN. 



Avrg. 40 



11.66 



potatoes, and the instruments hung 

 above the field of oats where the plants 

 were about 4 inches high. The next 

 table gives the results obtained. 



EVAPORATION ONE FOOT ABOVE THE SURFACE OF A 

 FIELD OF OATS AT DIFFERENT DISTANCES TO 



THE LEEWARD OF A SCANTY HEDGEROW. 

 Distance from Hedgerow. Evaporation in One Hour. 



Feet. C. C. 



20 10.3 



150 12.5 



300 13.4 



300 



14.4 



From this table it is seen that the 



In this case the evaporation at 300 



feet from the hedgerow was 30 per 

 rate of evaporation was 23.4 per cent. cent greater t h an at 2O f eet> an d 7.2 

 greater at 300 feet than at 40 feet, cent _ greater than at I5O f eet , an d 



basing the computation upon the aver- 



ages. 



In another locality the evaporome- 

 ters were set up at distances ranging 

 from 20 to 500 feet to the leeward of 

 a piece of black oak woods where 

 they had an average height ranging 

 between 15 and 25 feet and were 

 thicker on the ground. The results 

 secured during an hour of sunshine in 

 the middle of the day are given in the 

 table which follows : 



EVAPORATION ONE FOOT ABOVE THE SURFACE OF 



GROUND IN A FIELD OF OATS AT DIFFERENT 



DISTANCES TO THE LEEWARD OF A BLACK 



OAK GROVE OF TREES 15 TO 25 FT. HIGH. 



Distance from Woods. Evaporation in One Hour. 



Feet. C. C. 



20 n. i 



100 14.3 



200 15.7 



300 18.5 



500 18.3 



In this series the evaporation ap- 

 pears to have become constant at about 

 300 feet from the woods and was 

 some 66 per cent, greater than at 20 

 feet distant. 



The effect of a scanty hedgerow 

 was also measured. This was com- 

 posed of a strip of blue grass 16 feet 

 wide in which there were scattered 

 black and burr oak from 6 to 8, and 

 occasionally 12, feet high. The hedge 



the results make it clear that even 

 scanty hedgerows exert a measurable 

 influence upon the rate of evapora- 

 tion at considerable distances to the 

 leeward. 



INFLUENCE OF A CLOVER FIELD UPON 



THE RATE OF EVAPORATION TO 



THE LEEWARD. 



Adjacent to the naked field behind 

 the hedgerow just considered, there 

 was a field of clover 360 feet wide 

 along the margin of the oats and ex- 

 tending 780 feet back from it, across 

 which the wind passed in its course 

 from the north. At the same time 

 the last observations were made a sim- 

 ilar series w r as taken to the leeward 

 of the clover, the results being those 

 given in the following table : 



KVAPORATION ONE FOOT ABOVE THE SURFACE OF AN 



OAT FIELD AT DIFFERENT DISTANCES TO 



THE LEEWARD OF A FIELD OF CLOVER. 



Distance from Evaporation in 



Clover Field. One Hour. 



Feet. C. C. 



20 9.3 



150 1J. I 



300 13.0 



These results indicate that at 300 

 feet to the leeward of the clover the 

 rate of evaporation exceeded that at 

 20 feet 39 per cent, and that at 150 



