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<br />. and flood of record resulted in a belief that extreme flooding on streams in northwestem Colorado occurs <br />from large rainstonns or rain-on-snowmelt. The analysis was done to estimate the rainfall contribution to <br />the 1921 peak flow. <br /> <br />A graph of normalized-daily values of temperature and rainfall at Steamboat Springs and streamflow in <br />the Yampa River at Steamboat Springs for June 1921 is shown on figure 16a. The values were <br />nonnalized by dividing by the average monthly characteristic (eg., mean daily discharge divided by mean <br />discharge for the month) so that a comparison of temperature, rainfall, and streamflow can be made. There <br />was little rainfall except for June 14, 1921, Streamflow increased related to the rainfall coincident with the <br />annual peak-snowmelt runoff. Although late-June temperatures remained high or higher than the first half of <br />June (figure 16a; U.S. Weather Bureau, 1921), streamflow decreased substantially probably because the <br />majority of snowpack had melted. Other daily precipitation values for northwestem Colorado on June 14, <br />1921 were 1.07 in. at Hayden, 0.96 in. at Yampa, 0.74 in. at Pyramid, 0.37 in. at Columbine, 0.07 in. at <br />Lay, and 0.65 in. at Meeker. <br /> <br />Because of the importance of the accuracy of the 1921 flood estimate, an analysis was made of the <br />rating curve then in use and the 1919 to 1926 discharge measurements used to develop the rating curve. <br />The stage-discharge relation was very stable above about 1,000 ft3ls before and after the 1921 flood; <br />below this discharge there were small rating shifts annually. From 1919 to 1926, the maximum discharge <br />. measurement was 4,378 ft3/S at a stage of 5.18 ft, The 1921 peak discharge of 6,820 ft3/S was based on <br />a straight-line rating extension to the 1921 peak stage of 6,64 ft. This is reasonable as the flow was <br />contained within relatively vertical banks in the reach where the gage was located in 1921. Although the <br />rating curve was extended about 1.5 ft, it is unlikely that the peak discharge differs by more than about <br />100 to 200 ft3/S. <br /> <br />Other streamflow gages in operation in 1921 in northwestem Colorado also had near to or the largest <br />flow on record. Walton Creek near Steamboat Springs (09238500; drainage area is 42.4 mi2; elevation is <br />7,050 ft) had its flood of record of 2,800 ft3/S on June 15, 1921. Elk River near Milner (09242500; drainage <br />area is 415 mi2; gage elevation is 6,590 ft) near its confluence with the Yampa River about 6 mi west of <br />Steamboat Springs had the flood of record of 5,530 ft3/s on June 15, 1921. Further upstream, Elk River at <br />Clark (09241000; drainage area is 216 mi2; gage elevation is 7,268 ft) had its annual peak of 3,920 ft3/S on <br />June 7, 1921 and minimal rainfall runoff on June 15, 1921; the maximum peak flow of 4,910 ft3/S (from <br />snowmelt) occurred on May 23, 1984. The June 16, 1921 annual peak flow of 17,700 ft31s at the Yampa <br />River near Maybe" (09251000; drainage area is 3,410 mi2; gage elevation is 5,900 ft) was the third highest <br />peak; the largest peak flow of 25,100 ft3/S (from snowmelt) occurred May 17, 1984, The White River near <br />Meeker (09304500; drainage area is 755 mi2; gage elevation is 6,300 ft) had the third large peak flow of <br />6,370 ft3/S on June 16, 1921; the maximum peak flow of 6,950 ft3/S occurred on May 25, 1984 (from <br />snowmelt). <br />. <br />Prior to installation of a continuous-stage recorder on the Yampa River at Steamboat Springs in <br /> <br />25 <br />