OCR Text |
Show Several of the other organizations and agencies using Colorado River water also make independent estimates of the probable annual or summer discharge of the river. The investigation of this subject for the Upper Colorado River Commission was begun by studying the Roaring Fork of the Colorado. This stream heads in Pitkin County, Colorado, west of the continental divide between Aspen and Leadville and north of the divide between Aspen and Gunnison where the average annual precipitation exceeds 30 inches, at elevations of 10,000 feet and more. The gaging station near the mouth of the stream at Glen-wood Springs is below a point where the discharge of some hot springs maintains ice-free conditions throughout the winter. The gage is therefore always accessible, discharge records are usually excellent and they are of sufficient length so that reliable results should be obtained. Of equal importance is the fact that, through the cooperation of the office of the Water Resources branch of the U. S. Geological Survey, it should be possible to secure reports on the discharge of this tributary of the Colorado River soon after the first of each month of the year from February to May, for use in making actual forecasts. While forecasting studies for this stream are as yet incomplete, principles and conditions which should be of general application in the Upper Colorado River Basin are being obtained, so that the preliminary work for other tributaries in our river system will be materially less than at the beginning of this study. The general procedure adopted for this investigation was to begin with several trials of simple correlations between the summer discharge of the Roaring Fork at Glenwood Springs and the most important of the numerous hydrologic factors which constitute the source and cause the major variations in that runoff. Then a series of two or more of the most important of these factors, taken together in a multiple correlation, is computed and the results compared. After numerous trials the combination which produces the most accurate and reliable results will be used until still further study develops a more complete and satisfactory formula. This is the same procedure which has been used in the investigations on the use of the inflow-outflow method. The best formula thus far derived for the estimated discharge of the Roaring Fork at Glenwood Springs for the six months of April through September is based upon the discharge at this point for the six months of winter flow, October through March, the average water content from the snow surveys as of April first in -39- |