34 DIVISION OF WATER RESOURCES 



Because of ground water conditions, it was not deemed advisable 

 to set the Mariotte tanks under<;round for protection from temperature 

 changes as at Santa Ana. Instead, each tank was placed above ground 

 enclosed in a white painted board shelter. This is shown in Plate III. 

 Each shelter box has a narrow doorway opening before the glass gage 

 and a hinged top to allow access for refilling the tank when empty. 

 To provide insulation against temperature changes as much as possible, 

 the space between the tank and the sides of the box are filled with wood 

 shavings and the tank is wrapped with asbestos paper. 



Evaporation was measured from a standard Weather Bureau pan 

 mounted on a timber grill and from a ground tank 23iV inches in 

 diameter by 2.7 feet in depth. This tank was set mth the rim 3 inches 

 above the ground surface and the water surface was held near the 

 ground level. All eva])oration readings were obtained with a hook 

 gage equipped with a vernier reading to thousandths of a foot. A 

 four-cup anemometer was mounted on the platform of the pan, with 

 the cups about 12 inches above the top of the pan. 



A single tank, 23iV inches in diameter by 2.7 feet in depth, was 

 used in which consumptive use of water by round stem tules in sub- 

 merged soil was measured. It was set in the ground with about 3 inclies 

 of the rim exposed and connected to a supply tank through a float 

 arrangement, previously described. A glass gage and a graduated 

 scale mounted on the side of the supply tank allowed measurements 

 of water withdrawn for plant use. 



Additional equipment consisted of maximum and minimum tlier- 

 mometers housed in a standard shelter and an 8-iuch rain, gage: 



PRADO STATION 

 Description of Site 



A small station was established near Prado on the Santa Ana River, 

 midway between Santa Ana and San Bernardino, during the sunnner 

 of 1930, for collection of meteorological records, measurement of evapo- 

 ration from a water surface, and consumptive use of water by trian- 

 gular stem tules. The site is on slightly sloping ground near the lower 

 end of the Prado basin and is fully exposed to sun and wind. 



The climate is intermediate between the interior climate at the 

 San Bernardino station and the coastal climate at Santa Ana, as it is 

 tempered by the ocean breezes blowing through the Santa Ana canyon 

 into the Prado basin. This station Avas operated in cooperation with 

 the U. S. Geological Survey. 



Station Equipment 



The Prado station is equipped with a standard Weather Bureau 

 evaporation pan, a ground tank growing tules for measurement of 

 consumptive use of water, a thermograph housed in a standard shelter, 

 a rain gage, and an anemometer. The evaporation pan and the tule 

 tank are each equipped with a supply tank connection operating 

 through a float valve arrangement to supply and maintain a constant 

 water level in the pan or the tank. T'^se of water in each case is meas- 

 ured on the chart of a w^ater stage recorder mounted with a float in the 

 supply tank. This arrangement operates satisfactorily, the hourly 

 rate of use being computed from the chart. A barograph also is used 



