WATER LOSSES FROM WET AREAS 



99 



Wind action affects the instrument, since the change in air pressure, 

 as each gust passes, causes a vertical movement of the pan and pro- 

 duces a wavy line on the chart. In this way a continuous record is 

 obtained of the time the wind blows and also a relative indication of 

 its intensity. 



During cold winter months the water in the shallow pan freezes 

 solid, and an accurate record of the evaporation from an ice surface 

 may be obtained since the mechanism is of the weighing type. 



PLATE XXV 



t J: 



X. 



n t--tf7C7 o/'v ■ :■ vd? T-~-- 



EVAPORIMETER CHARTS. 





EVAPORATION AND TRANSPIRATION LOSSES ALONG THE 



STREAM CHANNEL 



Loss from Stream Between Controls 



The loss from a section of canyon was obtained by subtracting the 

 volume of water leaving from the volume of water entering the section. 

 Because of a possible storage differential in the section between the 

 beginning and the end of any period, this method will result in small 

 departures from the true dift'erences in short periods, such as a 24-hour 

 period, but in longer periods this difference will be negligible. 



That this differential storage exists is shown by Plate XXVI, 

 which presents a graph of the fluctuation in the water table September 



