75 



water supply. The effect of such vegetation on depletion of flow- 

 ing streams becomes increasingly important as water becomes scar- 

 cer and more valuable. 



Lack of data on consumptive use of water by canyon-bottom 

 growth led in 1931 to an investigation in selected sections of 

 Coldwater Canyon, near San Bernardino, Calif., to determine 

 stream losses chargeable to this type of vegetation. The initial 

 investigation covered a section of canyon 2,090 feet in length 

 between elevations 2,300 and 2,500 feet, the average bottom width 

 being 49 feet. The area comprised 2.36 acres of typical canyon- 

 bottom growth. Within this area vegetation depended for water 

 entirely upon the flow of Coldwater Canyon. Beyond the influence 

 of the stream the vegetation changed rapidly from alders and 

 sycamores to dry-land chaparral. During the second year studies 

 were extended upstream to include also an upper canyon section 

 immediately adjacent to the lower section. This lay between ele- 

 vations 2,500 and 3,100 feet; it averaged 44 feet in width and 

 was 5,875 feet in length. Thus in the second year the investiga- 

 tion included nearly 8,000 feet of canyon bottom. The area of 

 the upper section covered 5.89 acres of growth nearly similar in 

 type to that of the lower section. A vegetative classification 

 of both upper and lower sections, shown in Table 16, gives alder 

 as predominating, with California laurel showing the next highest 

 percentage of total growth. The under story consisted of scatter- 

 ed grapevine, blackberry, poison oak, and fern bracken. Plate II- 

 B shows alders growing between the lower and middle controls. 



Bedrock controls at the upper and lower ends of each sec- 

 tion insured complete measurement of all water in the canyon. 

 Parshall flumes were installed with water-stage recorders for 

 the earlier records, but for greater convenience these were later 

 changed to direct flow recorders. The small flow in dry seasons 

 made necessary a modification of the Parshall flume that would 

 measure accurately low flows in summer as well as maximum flows 

 during spring floods. For this purpose the Division of Irrigation 



