Laserfiche WebLink
<br />The importance of Pueblo Dam flood regulation comes into <br />operation for wide-spread rainstorm conditions over the upper <br />Arkansas River basin. Under these conditions, Pueblo Dam is <br />assumed to begin flood storage early enough that the downstream <br />flows on the river can be kept below the channel capacity. This <br />situation will allow for greater attenuation of tributary flood <br />peaks. This assumption is the basis for selection of the <br />modified curve on figure 4. <br /> <br />Flood Elevations <br /> <br />To determine the flood elevations on the Arkansas River at <br />and immediately above the Highway 50 bridge, north of Las Animas, <br />one-foot contour topography provided by the Corps of Engineers <br />was used. This topography was supplemented by field surveys of <br />the area south of the proposed flood levee. This topographic <br />data was used to prepare the channel cross-sections shown on <br />figure 5. The channel elevations at the upstream side of the <br />Highway 50 bridge and the channel slope were also determined by <br />field survey in April 1975. <br />From these cross-sections located at, 1000 feet, and 2000 <br />feet upstream of the Highway 50 bridge, elevation-area tables(3) <br />were prepared and the 100-year flow of 47,000 cfs was routed <br />through these sections. The profile of the flood flow is shown <br />on figure 6. This profile indicates backwater from the bridge <br />extending upstream through the 2000-foot section. Upstream of <br />this point, the profile is assumed to equal the 10 foot per mile <br />profile of the 1955 flood. The calculated elevations through <br />the cross-sections are based upon the assumptions that the <br />channel bottom will remain as it presently is and that there will <br />be no debris clogging the bridge opening. <br />The elevation at the upstream side of the bridge is calcu- <br />lated to be 3894.8 feet. This is 1.2 feet above the 1955 flood <br />elevation for approximately the same discharge. The reason for <br />this water surface rise is the progressive aggradation of the <br />of the channel above John Martin Dam. As previously mentioned, <br /> <br />14 <br />