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<br />20 THE ARKANSAS RIVER ,FLOOD OF ,JUNE 3-5, 1921. <br />-.~ -. <br /> <br />aged and the average slope between them being used. The discharge <br />through the upper, middle, and lower sections was also determined by <br />nveraging the hydraulic factors for all three cross sections and using <br />the average slope between the upper and lower sections. Thus, three <br />separate determinations of the discharge of each stream were made. <br />In general, the discharge given by the last-mentioned determination <br />was used. oWhere the difference in area between the upper and lower <br />cross sections made a marked difference in the velocity through each <br />section, a correction for velocity of approach was applied to the slope <br />between them. <br />Although the conditions of flow were not the same for all cross sec- <br />tions the main channels were uniformly free from vegetation, and as <br />\he 'overflow areas were only a small percentage of each CI'OSS section <br />'the value for the coefficient' of roughness (n) was taken as 0.035 for <br />the tributary streams and 0.030 for Arkansas River above Pueblo. <br />The best section of Arkanslls River for using the slope method of <br />measurement is just west of Pueblo and above Dry Creek. In this <br />locality three cross sections of the river valley between well-defined <br />high-water marks were measured. The low,er section waS opposite <br />the lower end of the North Side settling basin of the city water- <br />works; the middle section 1,230 feet upstream, at the upper end of <br />the settling basin; Hnd the upper section 1,740 feet farther upstream, <br />On computing the mean slope between the different sections the <br />slope between the middle and lower sections waS fonnd to be 50 <br />slight that it was believed to be within the influence of backwater <br />from Pueblo and was discllnled. 'The slope for a mean distance of <br />1,740 feet between the upper and middle sections was fonnd to be <br />0.00125, and the maximum discharge was det~~rmined from the mean <br />of the areas of the two cross sections as 83,500 second-feet. <br />To determine the maximum discharge at J'ueblo it was necessary <br />to add the flow ent~ring from Dry Creek. It was impossible to de- <br />termine definitely the amount of water in Dry Creek at the time <br />of the peak flow in Pueblo, as Dry Creek had two floods, one during <br />the night of June 2-3 llnd one the evening of .Tunc 3, The maximum <br />discharge of the stream in the first flood was found to be 24,400 <br />second-feet, and as the secono flood was somewhat less the discharge <br />at the time of the Pueblo peak was assumed to be 19,500 second-feet. <br />By adding this assumed discharge of 19,500 second-feet in Dry <br />Creek to the discharge of the Arkansas aboy€: Dry. Creek the ma.xi- <br />mum discharge of the Arkansas at Pueblo was found to be 103,000 <br />second - feet. <br />The results of the field work are given in the following table; <br />