OCR Text |
Show flow would be a welcome change from the poor conditions of the past two seasons." A few forecasts from the above report are tabulated below. FORECAST 10 yr. av. % of 10 flow 1000 ac. ft. yr. av. 1000 ac. ft. Colorado River near Cameo, Colo. 4,350 145 3,100 at Lees Ferry 16,000 127 12,630 Roaring Fork at Glenwood Springs 1,240 130 952 Green River near Linwood, Utah 1,200 83 1,445 at Green River, Utah 4,700 111 4,250 San Juan River near Farmington 2,150 116 1,850 near Bluff, Utah 2,350 112 2,090 Altogether forecasts are published by the Weather Bureau for some 40 points on the Colorado River and tributaries in the Upper Basin. The forecast for the flow at Lees Ferry as of February 1, 1951 was 16,000,000 acre feet, and in the issue for March 1, it was only 10,400,000 acre feet. For the April 1 forecast the estimate had been reduced to 9,300,000 acre feet and in the May report it was 9,500,000 acre feet. The actual discharge for the year, as given in the February 1, 1952 bulletin just received, was 9,817,000 acre feet. This indicates the very great increase in the accuracy of any forecast as the time at which the forecast is made becomes later and later in the year. The May forecast was about 97 % of the observed runoff at Lees Ferry. On the other hand, the February estimate was about 60% more than the actual amount while that made March first was only 6% too high. This is given to point out the relative unreliability of very early estimates of stream flow. A forecast for the inflow to Lake Mead is made early in each month from January to May, by the Office of River Control of the Bureau of Reclamation at Boulder City, Nevada, copies of which are also made available to the Commission. These forecasts are prepared for use in the operation of Hoover Dam and Lake Mead especially for the purpose of flood control. The first paragraph of the two page forecast dated February 8, 1952, is quoted herewith. "1. Forecast Based on Precipitation (a) Precipitation over the Upper Colorado River Basin during January continued considerably above normal; therefore, prospects for the -37- |