Laserfiche WebLink
<br />17 <br /> <br />line was drawn through the points of each time period. <br />The discharge relationship from the records after 1934 is <br />parallel but one third lower than the discharge before 1934. <br />Gages 9-0470, 9-0630 and 9-0850 were analyzed to see <br />if the areas without controls showed a similar decrease. <br />Again the same time periods before and after 1934 were used <br />to study possible change in the calculated 50 year discharges. <br />See Annual Peak Flow graphs figures 17 thru 19 in the appendix. <br />The results of the comparison were: <br /> <br /> Q50 <br />GAGE NO. BEFORE 1934 AFTER 1934 REDUCTION <br />9-0470 1,450 cfs 985 cfs 32% <br />9-0630 1,120 805 28% <br />9-0850 17,990 16,700 7% <br /> <br />These gaging stations represent about one-fifth of <br />the drainage area above DeBeque Canyon. The most signifi- <br />cant gage is 9-0850 at Glenwood Springs because it is the <br />largest drainage area of the three gages not affected by <br />controls and diversions. Using the drainage area as a basis <br />to proportion the reduction, these gages have an average <br />reduction of 8% in the peak flows. <br />It is logical to attribute this reduction to climatologi- <br />cal change. Therefore the 33% reduction of the 50 year flood <br />as calculated from the Colorado River gaging stations is not <br />entirely from diversions and controls. At least 8% can be <br />attributed to olimatological change. Thus diversions and <br />controls account for a 25% reduction in the 50 year flood. <br />In our opinion, however, the present controls and diversions <br />would have less influence on a high frequency (100 year or <br />