97 



6 feet in diameter set in a thicket of the same growth. The 

 water table in the tank fluctuated slightly throughout the season 

 but averaged about 13 inches below the surface. Consumptive use 

 for 12 months amounted to 30.49 inches in depth for the area of 

 the tank. Evaporation records are not available for all this 

 period, but for the first 6 months, June to November, inclusive, 

 consumptive use by the willows was 47.9 per cent of the evapora- 

 tion from a Weather Bureau pan. A similar test in southern 

 California, involving an isolated tank unprotected by other 

 willow growth in which depth to water was 2 feet, resulted in a 

 consumptive use of water equalling 92.7 per cent of the evapora- 

 tion loss from a Weather Bureau pan. 



Summarizing vegetative use of water at Isleta: Cattails 

 and sedge are extravagant users of water, while saltgrass and 

 willows use less. This conclusion is supported by similar inves- 

 tigations elsewhere. 



Mesilla Valley, New Mexico 



The evaporation-transpiration station established at 

 Mesilla Dam to determine consumptive use of water by cattails and 

 saltgrass was on low ground along the west bank of the Rio Grande 

 in an area of similar growth. The site was made available by the 

 Bureau of Reclamation. There was exposure in all directions ex- 

 cept to the west where the mesa rose abruptly about 15 feet some 

 50 yards from the station. To the south were a few scattered 

 trees, while the river bordered the northeast side. A sketch of 

 the station site is sho-wn in Figure 13. 



Cattails . --Two cattail tanks were located in a swamp com- 

 pletely surrounded by natural gro'Arth. Tanks were 2 feet in diam- 

 eter by 3 feet deep. Healthy broadleaf cattails were transplanted 

 into the tanks and the water surface was maintained approximately 

 2 inches above the soil. Each developed a vigorous growth al- 

 though the plants were somewhat larger in one tank than in the 

 other. This difference is reflected in consumptive use, as will 



