59 



water table. 



Grass and weeds . -^--On grass and weed plots some penetra- 

 tion beyond the area of root activity may be expected on the 

 coarser soil types when precipitation exceeds 10 to 12 inches. 

 Here again the distribution of seasonal rainfall is an important 

 factor in deep penetration. A contributing factor also is the 

 density of growth. No run-off occurred from either brush or 

 grass plots. In a majority of plots consumptive use by grass and 

 weeds equalled the precipitation. Use of water by grass and 

 weeds under similar conditions is slightly less than by brush and 

 ranges from 12.58 to 15.49 acre-inches per acre. The factor of 

 rainfall likewise limits these values. A summary of the grass 

 and weed studies is shown in Table 10. 



Mo 



jave Valley, California — ' 



Tules . --Studies on the Mojave River at Victorville, Calif, 

 were undertaken in 1930 with triangular-stem tules transplanted 

 into 2 tanks set deep in a tule swamp and in a third tank nearby 

 which was exposed to surrounding desert conditions. Evaporation 

 from a Weather Bureau pan and meteorological data were obtained. 

 Tule tank No. 1, 2 feet in diameter by 3 feet deep, was set in 

 the ground in an open space removed from the swamp influence to 

 which other tanks were subjected. Tanks Nos. 2 and 3, surrounded 

 by dense swamp growth, were 2 and 6 feet in diameter respectively 

 by 3 feet deep. Figure 7 shows a sketch plan of the Victorville 

 station and the general arrangement of supply tanks and soil 

 tanks . 



Under such conditions data obtained from the swamp tanks 

 represent actual swamp consumptive use, and it is possible to 

 establish a relation with exposed and isolated tule growth and 

 also with evaporation from a Weather Bureau pan. The investiga- 

 tion continued through 1931 and 1932. 



TJ See footnote 1, p. 55"^ 



