Table 5. 



— Water yielded from the East and West Branch watersheds expressed as percent of 

 annual precipitation (1965-1970) 



Item 



1965-66 1966-67 



Water year 

 1967-68 1968-69 1969-70 



East Branch 

 West Branch 



Annual precipitation 



17 

 29 



33.13 



18 



36 



49.44 



-Percent 



19 

 38 



■Inches ■ 

 49.89 



25 

 47 



51.62 



23 

 44 



50.14 



that "V" gages were used, based on the flow 

 prior to freezeup. Our measurements of win- 

 ter flow obtained from the heated gaging sta- 

 tions indicate that winter flow was materially 

 underestimated in the past, especially from 

 the West Branch. 



We used the techniques presented by 

 Kovner and Evans (1954) to determine the 

 length of calibration period needed to accur- 

 ately predict various levels of expected post- 

 treatment change in streamflow. Using 5 years 

 of streamflow data and based on an error vari- 

 ance of pretreatment flow of 0.714 inch, we 

 calculated that we should be able to detect an 

 8 percent change in annual flow (1.48 inches) 

 at the 95 percent confidence level. Based on 

 these analyses, the two watersheds appear to 

 be well calibrated, but since no treatment is 

 planned before the summer of 1973, the pre- 

 treatment calibration period will be extended 

 to 6V2 years. 



How much of an increase in streamflow 

 can we expect? This is a difficult question, 

 and the answer depends on the type of treat- 

 ment used and area to which it is applied. We 

 know that when aspen was defoliated in 

 southern Utah, annual streamflow from a 

 447-acre treated area increased from 0.5 to 

 3.5 inches during the posttreatment period. If 

 we extrapolate the water savings indicated by 

 our plot studies (Johnston 1969, 1970) to a 

 100-acre treatment area, we would theoreti- 

 cally realize a reduction in soil moisture de- 

 pletion of about 8 inches of water per acre or 

 about 66 acre feet. If all the water saved were 

 released as streamflow, annual flow from the 

 West Branch would be increased about 24 per- 

 cent. This extrapolation is, of course, over- 

 simplified and subject to considerable error. It 

 is used only to illustrate the potential for in- 

 creasing water yields and to point out the 

 need for a watershed size study. 



Table 6. — Linear regression analyses using several streamflow parameters for the Chicken 

 Creek watersheds 





Equation 



Input 





N 



Y = 



2.04 X -1.377 



Annual flow 



0.982 



5 



Y = 



0.5447 X +0.324 



Annual flow + 6 yrs. of "V" notch data. 



0.922 



11 







1952-1958 







Y = 



1.858 X +0.043 



Monthly flow 



0.977 



60 



Y = 



1.94 X -0.126 



Annual April-July high flow period 



0.970 



5 



Y- 



2.156 X -0.562 



Annual August-March low flow period 



0.922 



5 



22 



