WSP01635 - Laserfiche WebLink

Home Browse Search

.OJ3477 24 involving the whole area were large enough to produce a sizeable response in flow measured at Glen Canyon. Streamflow reference material used was the "Present Modified Streamflow of the Colo- rado River at the Glen Canyon Dam Site. 11 (Unpub- lished data supplied by Mr. R. Riter of Bureau of Reclamation, Denver). c. RESULTS It was found that any major storm which af- fected the three sub-basins had but less than 15 inches total from the 18 stations tended to have little immediate effect on subsequent streamflow measured at Glen Canyon. Although it is highly desire able that some adjustment be made for the time of year when the storm occurs when deciding on its relative importance to streamflow, for pur- poses of this particular analysis a fixed value was used for the entire year. In Figure 33 we find the 15 storms which have occurred in the 46 -year period having total pre- cipitation amounts above 15 inches as measured at the 18 stations in Western Colorado. It was somewhat surprising to find that in four of the seasons more than one such storm oc- curred. Referring to Figure 33 we note that in the T ABLE V water year of 1913-14 there were three storms separated by two months or more which produced 15 inches in two or three days respectively. While it is true that the storm of September 22-23, 1913, actually prod~ced precipitation prior to October 1, the streamflow response measured at Clen Canyon would hav.e been in the 1914 water year. A similar situation occu.rred in late Septem- ber of 1915 when the storm occurring between the 24th and 26th could not have produced any large in- crease in runoff measured at Clen Canyon until after October 1. The situation in 1929 was some- what different in that the storm occurred the early part of September and a goodly portion of the in- crease in runoff was measured in that same month at Glen Canyon. This was, however, a case in which some of the precipitation in September did influence the following water year and produced abnormally high amounts of runoff for the res pee - tive quantity of precipitation measured in 1929-30 water year. Table V furnishes a very rough approximat(on of the resulting change in annual streamflow mea3- ured at Glen Canyon during water years when the major storms occurred as listed in Figure 33. The simple method of analysis was to determine the percentage relatiom,hip of precipitation totals -- including the major storms --in each of the various Rough approximation of response in increased annual streamflow at Glen Canyon related to major storms occurring in Western Colorado. (Stream-flow Unit - 1000 acre-feet). - Percentage Water Year of Annual Resulting Rnnoff Actual Extra Containing Average when same Percent- Water Runoff 1 or more Precipitation age is Applied to Year which may Major Storms Recorded 46-Season Average Runoff be due to (See Fig-. 33) Oct. - Sept. Runoff of 12,640 Recorded Major Storms 1914 112 14,157 18,007 .+"-3,850 1920 111 14,030 18,818 + 4,788 1912 114 14,410 17,421 + 3,011 1942 101 12176B 16,394 + 3,628 1952 la 15,421 17,613 + 2,192 1946 104 13,146 13,224 + 78 1927 139 17,570 15,570 - 1,780* 1929 133 16,811 18,387 + 1,576 1915 93 11,755 11,605 150 1916 115 14,536 16,307 + 1,771 ..' Three-basin major storm in June and special 14-day rainy period in September resulted in + 3,104 excess streamDow following year when annual precipitation was 90 per cent. The combined t\l:O- season net excess is -+- 1,324.