116 DIVISION OF WATER RESOURCES 



seasonal drop in the discharge to a low point in August and a recovery 

 during September and October before any rain of importance has 

 occurred. 



October 9, 10, 11, 1931, were cool cloudy days and the transpira- 

 tion loss was very low and the maximum daily flow increased to 0.46 

 second-foot at the middle control. In contrast to this, August 24, 25, 

 and 26, in the same year, were three days at the end of a long period 

 of hot weather, and on the mornings of August 25, 26, and 27 the maxi- 

 mum flow was only 0.25 second-foot at the middle control. The dif- 

 ference between 0.46 second-foot and 0.25 second-foot, or 0.21 second- 

 foot, represents a loss of water originating in these small springs, but 

 this flow was entirelj- intercepted so that none of the water represented 

 by this value of 0.21 second-foot reached the middle control at any 

 time on August 24, 25, and 26. A flow of 0.21 second-foot is equiva- 

 lent to 5.0 acre-inches per da3\ This is a loss that might be reclaimed 

 if each spring were sought out and developed at its source. The draft 

 on the connected flow measurable by the dip in the discharge curve at 

 the middle control on August 24, 25, and 26 is given in Table 40 

 and averages 3.1 acre-inches per day. The loss between the middle and 

 lower controls on those three days averaged 1.0 acre-inch per day. 

 This makes a total of 9.1 acre-inches per day, for the average loss per 

 day on August 24, 25, and 26 in 1931, and is chargeable to evaporation 

 and transpiration between the springs, where the water first comes to 

 the surface, and the lower control. 



The source of the summer flow is within an area of 0.2 square 

 mile between elevations of 3100 and 4250 feet in the stream bed. The 

 drainage area back of the stream bed elevation of 3100 feet is 1.3 

 square miles and the elevation of the divide ranges from 5200 to 5800 

 feet. The seasonal precipitation recorded at Alpine at an elevation 

 of 5750 feet was 53.66 inches in 1931-32, yet the first steady spring 

 flow in Coldwater Canyon is below an elevation of 4250 feet. 



The flow at the lower control was never as great as that measured 

 at the upper control during the period of measurement from July 15 

 to November 3, 1932. The significance of this fact is that there was no 

 effective yield of water as summer flow from the portion of the water- 

 shed tributary to the stream below the upper control, which portion is 

 62 per cent of the watershed area above the lower control. Since there 

 was no gradual gain in flow as the stream passed through the 7965 feet 

 of canyon between the upper and lower controls, it indicates that prac- 

 tically all the moisture from rainfall that might have been slowly 

 moving downhill through the soil mantle over this lower portion of 

 the watershed was intercepted by the vegetation before it reached the 

 canyon bottom. 



COMPARISON OF USE BETWEEN CONTROLS WITH 

 METEOROLOGICAL DATA 



During the 1932 season records were obtained from an air 

 thermograph, maximum and minimum thermometers, and an atmometer 

 located near the mouth of the canyon, and also from an atmometer 

 located near the lower control in the canyon. 



Monthly mean maximum and minimum temperatures are shown in 

 Table 42 for the months of record in 1932 at the mouth of the canyon. 



4 



