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. . 116 CONTRIBUTIONS TO HYDROLOGY OF UNITED- STATES, 1923-IIl24. that the rainfall was a steady downpour rather than a series of short storms of cloudburst intensity. The chief damage caused by the flood was in the Big Horn River basin, although a considerable stretch of the new roadbed of the Chicago, Burlington & Quincy Railroad near Bonneville was washed out. At Thermopolis the lower ground was flooded, but as the flood was 1.3 feet lower than that of July, th~ damage was not so extensive. The railroad fill south of the station at Manderson was washed away and the water entered the town and flooded it to a depth of 2 or 3 feet. People living on the lowlands near Basin and Greybull were forced to move. Many of the streets in Greybull were covered with water to a depth of 3 feet, Part of the fill between the two highway bridges over the Big Horn at that point was carried away, thus increasing the the carrying capacity of the channel, A hydrograph of the flood (fig. 10) hils been prepared froni the records at the Thermopolis gaging statio,n. This graph shows that the river rose gradually from 6,200 second-feet at midnight September 26 to' 10,000 second-feet in 24 hours. . In the succeeding 26 hours the river rose to its maximum stage of 25,500 seCond-feet, which was reached at 2 a. m. September 29; it remalned at or near that stage for 10 hours and then 'steadily. fell to 8,800 .second"feet at 6 p. m. September 30 and to 5,000 second-feet by noon October 1. Iluring that period a tot81 of 110,000 acre-feet passed the station, Practically the entire drainage basin above Thermopolis con- tributed to the flood at that point. As the crest at Riverton occurred 12 hours earlier, the average rate of travel for the crest between Riverton and Thermopolis was 5 miles an hour, and as its volume increased from- 6,500 to 25,500 second-feet, all the intervening streams must have contributed. These streams, however, were not so high as during the July flood. _ The crest flow increased considerably through the Big Horn River basin as rains occurred over its entire area; and the tributaries, Jiotably Nowatllr arid Nowood' creeks, had moderate floods, the crests of which reached the Big Horn about the time of the .main crest itself. . - OOMPARISON BETWEEN FLOODS OF JULY AND SEPTEMBER, 1923. The following table summarizes the principal facts about the July and September floods: . - Comparison between floods of JuJ.y and September, 19119, on Big Horn River. 1uly crest September Point. ,,,.. .Remarks. (Ie"""'" (second-- feet). - .. (eet). Btverton. WYO_~""_h._______ 1~1OO .."" Muimum stage, 1.3 (eet lower LD SepbmJ,ber. Thermo~yo__.._n..u_ 29.800 25,500 Manderson, yo____________ -...'....000- .....;0;;00- Maximum stage, 1 foot higher in September. _Mont--_-__...,...... - Do. .