100 



DIVISION OF WATER RESOURCES 



7-15, 1932, in a ground-water pit located a short distance upstream 

 from the lower control and about ten feet from the stream. From this 

 graph it is seen that there would be a small storage differential each 

 day between September 9 and 12, but that this diiferential is almost 

 zero between September 8 and 9 and from September 12 to 15, and 

 that the storage differential over the entire period would be only an 

 extremely small portion of the use of water during the period. As 

 between September 8 and 15, the storage differential is represented by 

 0.85 inch. Assuming the specific yield to be 8 per cent, this represents a 

 depth of water of 0.068 inch which spread over 2.36 acres — the area 

 between the middle and lower controls — gives a volume of 0.16 acre-inch. 

 The total use between those controls for this period was 7.39 acre-inches. 

 Hence the differential storage over the entire period is only 2.2 per 

 cent of the total use of water for this period of one week, which is no 

 doubt higher than usual as a hot wind was blowing during the early 

 morning hours of September 8. For longer periods, such as a month, 

 the percentage would be considerably less. 



FLUCTUATION IN THE WATER TABLE IN COLDWATER CANYON, 



SEPTEMBER 7-15, 1932. 



To obtain the volumes of water passing each control not equipped 

 with a flow recorder it was necessary, in order to attain sufficient 

 accuracy, to take off hourly values from the water-stage recorder 

 charts. Later, when the flow recorders were installed, the daily volumes 

 of water passing each control could be planimetered directly from the 

 flow recorder charts. 



A section of the discharge curve at the middle control is shown in 

 Plate XXVII. This plate shows the record of discharge at the middle 

 control from August 9 to August 15, 1931. It includes four warm days, 

 August 9, 10, 11, and 15 ; one day on which rain fell, August 12 ; and 

 two cool, cloudy days, August 13 and 14. 



The eft'ect of evaporation is indicated by a comparison of the 

 evaporation from an evaporation pan, placed in the middle of the 

 stream so that water of the stream entirely surrounded the pan, and 

 the loss between the middle and lower controls. During the period 

 from September 8 to 14, inclusive, 1932, the average depth of evapora- 

 tion from this pan was 0.0076 foot per day. Assuming an average 

 width of stream surface of 3 feet the total volume whicli Mould be 

 evaporated in the length of 2090 feet between the middle and lower 



