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20 THE ARKANSAS RIVER FLOOD OF JUNE 3~5, 1921. --- - -- aged and the average slope between them being used. The discharge through the upper, middle, and lower sections was also determined by uveraging the hydraulic factors for all three cross sections and using the average slope between the upper and lower sections. Thus, three separate determinations of the discharge of each stream were made. In general, the discharge given by the last-mentioned determination was used. Where the difference in area between the upper and lower cross sections made a marked difference in the velocity through each section, a correction for velocity of approach was applied to the slope between them. Although the conditions of flow were not the same for all cross sec- tions the main channels were uniformly free from vegetation, and as 'the 'overflow areas were only a small percentage of each CI'Oi;S section 'the value for the coefficient' of roughness (n) was taken as 0.035 for the tributary streams and 0.030 for Arkansas River above Pueblo. . The best section of Arkansas River for using the slope method or measurement is just west of Pueblo and above Dry Creek. In this locality three cross sections of the river valley between well-defined high-water marks were measured. The lower section was opposite the lower end of the North Side settling basin of the city water- works; the middle section 1,230 feet, upstream, at the upper end of the settling basin j and the upper section 1,740 feet farther upstream. On computing the mean slope between the different sections the slope betweE:'n the middle and lower sections was found to be so slight that it was believed to be within the influence of backwater from Pueblo and was discarded. The slope for a mean distance of 1,740 feet between the upper and middle sections was found to be 0.00125, and the maximum discharge was determined from the mean of the areas of the two cross sections as 83,500 second-feet. To determine the maximum discharge at Pueblo it was necessary to add the flow entering from Dry, Creek. It was impossible to de- termine definitely the amount of water in Dry Creek at the time of the peak flow in Pueblo, as Dry Creek had two floods, one during the night of June 2-3 and one the evening of .Tune 3, The maximum discharge of the stream in the first flood was found to be 24,400 second-feet, and as the seconil flooc! was somewhat less the discharge . at the time of the Pueblo peak was assumed to be 19,500 second-feet. By adding this assumed discharge of 19,500 second-feet in Dry Creek to the discharge of the Arkansas above Dry. Creek the maxi- mum discharge of the Arkansas at Pueblo was fonnd to be 103,000 second-feet. The results of the field work are given in the following table: