24 DIVISION OF WATER RESOURCES 



1. Based on the 25-month period of record, the mean annnal con- 

 sumptive use of -water by tules growing in a tank 6 feet in diameter, 

 located in a swamp with natural conditions replicated, was found to be 

 78.5 acre-inches per acre. 



2. For the same period, the mean annual evaporation from a 

 standard Weather Bureau pan located on the bank near the swamp was 

 82.5 inches. By applying a conversion coefficient of 0.7 to this value, 

 the mean annual evaporation from a lake surface is indicated to be 

 58 inches. 



3. The ratio of the mean annual consumptive use of water by the 

 tules to the mean annual evaporation from the standard Weather 

 Bureau pan for the period of record is 0.95. 



4. Based on the mean record for the two growing seasons from 

 ]\Iay to October, inclusive, the evaporation from a lake surface is 

 indicated to be 40 inches, while for the same period the consumptive 

 use of water by tules would be 62 acre-inches per acre. This exceeds 

 the loss by evaporation from the free water surface of a reservoir by 

 22 inches. 



5. The investigation demonstrates the impracticability of applying 

 to field conditions records of tests made in isolated tanks of tules grown 

 apart from their natural environment. 



Coldwater Canyon Investigations 



The investigation into the lo.sses (tccurring along the stream chan- 

 nels above the usual points of diversion was started in Coldwater 

 Canyon near San Bernardino in 1931 and continued through 1932. The 

 combined evaporation and transpiration by the native vegetation grow- 

 ing in the canyon was determined by accurately measuring the water at 

 various points along the channel. The controls were on bed rock so that 

 the amount of water entering the upper end of each section of channel 

 was known as well as the amount leaving each section. 



The losses from two sections of the canyon are reported, the average 

 elevation above sea level of one being 2400 feet and of the other 2800 

 feet. The average width of the canyon bottom fill in the lower section 

 is 49 feet, and in the upper section it is 44 feet. 



The results of this study show a loss from the lower section of the 

 canyon of 72 acre-inches per 1000 feet of canyon for the six-month 

 period from May to October, inclusive, 1932. This is at the rate of 

 64 acre-inches per acre of canyon bottom fill. For the same period in the 

 upper section of canyon, the loss was found to be at the rate of 50 acre- 

 inches per acre of canyon bottom fill. 



The evaporation from the water surface in the stream is shown 

 to he only a small part of the total loss by evaporation and transpira- 

 tion. The water surface of this stream is almost completely shaded 

 and the evaporation rate would be greater in open areas where the 

 water surface is exposed to the sun. The maximum loss in the canyon 

 occurred during the month of August. 1932, being at the average rate 

 of 0.44 acre-inch per acre per day in the lower section, and 0.35 acre- 

 inch per acre per day in the upper section. In October the average 

 rate of loss was 0.26 acre-inch per acre per day in the lower section 

 and 0.20 acre-inch per acre per day in the upper section. 



Enough water is consumed during the growing season along each 

 mile of canvon similar to the lower section to meet the annual irrigation 



