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~ . 'I',:,' " '\<~ ~: .'" ~'; THE FLOOD AT PU~BLO. 29 " , This caused the peak flows from the near-by tributaries to reach Pueblo at the same time uS the peak flows from the more distant streams, producing the most favorable conditi.ons possible for a flood of great height. It is impossible to determine accurately the total discharge at Pueblo during the flood, owing to the great. size of the area over~ flowed, the breaks in the levee, and the scour in the main channel caused by the flood. The discharge up to the time the levees were overtopped and broke, about 9 p. m. June 3, can be determined satis- factorily, as a fair rating curve for the State gage is a \'ailable. For the remainder of the period only a rough estimate can be made. The peak flow at the maximum stage of 24.66 feet was 103,000 second- feet. (See p. 20.) To determine the discharge at the time the levees were overtopped it was assumed that of the total scour of 1.4 feet noted after the flood, about 0.5 foot had occurred at that time, and the flow through the breaks in the levees was estimated to be 10,000 second-feet. Although this estimate may be as much as 100 per cent in error the effect of such an error on the entire discharge would be very small. As explained on page 24, the levees were built to protect the city against a flood flow of 40,000 second-feet, which would reach a gage height of 18.1 feet. The additional flow permitted by the scour of 0.5 foot, however, would give a discharge of 40,000 second-feet at gage height 17.6 feet. Adding the 10,000 feet that escaped through the breaks would give a flow of 50,000 second-feet at gage height 17.6 feet. From this figure and the maximum discharge at 24.66 feet (103,000 second...feet) an approximate rating curve was plotted for use between 9 p. m. and midnight. , As the river fell the scouring action continued until at the time the, river was once more within its channel the gage height was 0.9 foot lower for the same discharge than it was when the break had just occurred. The lower part of the rating curve was defined by a measure- meri.t made by the State engineer's office at a stage of 5.6 feet, showing a discharge of 6,270 second-feet. By applying the above-described rating curve to the hydrograph the total discharge from 8 a. m. June 2, at the time the river first started. to rise, until midnight of June 5, after the flood had passed, was found to be 14:5,000 acre-feet. Of this amount 90,000 acre-feet was the total flow from noon of June 3 to midnight of June 4. It was impossible to determine the total discharge of the tributary streams.