91 



A measure of consumptive use is available through compari- 

 son with evaporation from a free water surface. Thus, evaporation 

 from a Weather Bureau pan for the J\ine to November period was 

 30.80 inches. Application of this value indicates that consump- 

 tive use by the tules was 126 per cent of the evaporation; by- 

 native meadow tank No. 2, 118 per cent; and by meadow grass with 

 a water table 8 inches below the surface, 99 per cent. It should 

 be remembered that these percentages are for but 6 months of the 

 year and do not represent annual values. At Victorville, Calif., 

 as previously reported, consumptive use by tules growing under 

 swamp conditions similar to those at Parma was 95 per cent of the 

 evaporation from a Weather Bureau pan computed on an annual basis. 

 For the period July to November, inclusive, this value would be 

 112 per cent instead of 95 per cent, showing that summer ratios 

 exceed those for the entire year. Consumptive use by tules and 

 meadow grass and pertinent meteorological data are shown in Table 

 23. 



Middle Rio Grande Valley, New Mexico 



This station was located on the east side of the Rio Grande 

 near the pueblo of Isleta in a low moist area containing such 

 water-loving plants as sedges, tules, cattails, saltgrass, and 

 willows (Pl.III-B). The observations were conducted in cooperation 

 with the Middle Rio Grande Conservancy District during 1936 and 

 1937. A sketch of the station is given in Figure 11. Mariotte 

 apparatus was used to supply water to vegetation tanks and keep 

 the water surface at constant levels, as indicated in Figure 12. 

 To provide a natural environment, each vegetation tank was set in 

 a surrounding growth of the same species. Tule tanks were placed 

 in a dense swamp, grasses in meadow land, and willow growth in a 

 willow thicket. Each species represented a large area of similar 

 growth in the Middle Rio Grande Valley. Consumptive use of water 

 by cattails, sedge, saltgrass, and willows, with meteorological 

 data, are shown in Table 24. 



