44 DIVISION OF WATER RESOURCES 



more. Tank No. 9. on the other hand, had a heavy mat of short 

 stemmed grass which did not compare in height with the new growth. 



Records were kept of the consumptive nse of water nnder these 

 conditions from j\Ia.y, 1929, to October, 1930, when the water table 

 was raised from 2 feet to 1 foot, remaining at this level until the end 

 of the investigation. From the very beginiiing, these tanks had moist 

 soil surfaces on which accumulations of powdery alkali occurred, and 

 with the rise in the water table, this became more pronounced. The 

 concentration, however, was not sufficient to cause injury to the salt 

 grass, which increased in height and density with the higher water 

 table. 



Tanks Xos. 10, 11, and 12, comprising the fourth set, were covered 

 with the original salt grass sod found growing on the surface when 

 the tanks Avere filled, and therefore had fully developed root systems 

 from the beginning. Prom the first this groAvth was very dry and 

 sparse and did not increase in density when additional water was sup- 

 plied. The initial water table was at a depth of 4 feet and consump- 

 tive use of water measurements were made under these conditions from 

 May, 1929. to October, 1930, when the water table was lowered to 5 

 feet. At this depth the experiment was continued until the investiga- 

 tion was completed. As the water table was always below the limit of 

 capillary rise, the tank surfaces remained dry in contrast with others 

 which were always moist. In consequence, there was little or no soil 

 evaporation and no surface deposit of alkali. 



Tanks Nos. 13, 14, and 15 were installed during the summer of 

 1929, for the purpose of comparing evaporation from soil in tanks 

 filled by different methods. The comparisons were to be with Tanks 

 Nos. 4, 5, and 6, ]n-eviously described. Each set had the same depth 

 to water, the same bare surfaces, and contained the same type of soil, 

 except that Tanks Nos. 4, 5, and 6 contained undisturbed soil, while 

 Nos. 13, 14, and 15 were loosely tilled. 



These comparisons of evaporation from soils of different structural 

 arrangement were continued until October, 1930. At this time the 

 soil evaporation studies were discontinued and all bare tanks were 

 transplanted to salt grass for further comparative studies. After both 

 sets of tanks were transplanted to salt grass, the comparison was con- 

 tinued without changes in depth of water tables until the investigation 

 was discontinued. Both sets of tanks produced good growths of grass, 

 although that grown in the loose soil was not as heavy as that grown 

 in the undisturbed soil. 



In addition to use of soil tanks with ^Nlariotte connections for 

 evaporation and consumptive use of water studies, several tanks of 

 simple design were used for growths of tules, willows, and wire rush. 

 As tules are aquatic plants accustomed to grow in swamps with their 

 roots submerged, the tanks in which they were grown were maintained 

 with water tables about 2 inches above the soil level. The height of 

 the water table was determined by an index point in each tank. In 

 the smaller tanks the water table was raised to the index point each 

 morning by using a measured anu)unt of water. In larger tanks this 

 involved a greater amount of work and supply tanks were operated to 

 maintain llic proper water level and supply water as used. In the 



