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<br />highway bridge, 0.4 feet higher than the 1955 flood with only one <br />half the amount of water. This higher elevation is due to the <br />progressive aggradation of the river channel north of Las Animas. <br />This aggradation has been occurring since the 1921 flood and <br />the spread of the salt cedar in the floodplain. However, since <br />the 1955 flood, the channel has filled between four and eight <br />feet at the highway bridge. <br /> <br />Flood Control Measures <br /> <br /> <br />Several measures have been taken or proposed to reduce the <br />Arkansas River flood hazard to the City of Las Animas. The Corps <br />of Engineers and the City of Las Animas have periodically made <br />improvements to the channel upstream and downstream of the Highway <br />50 bridge. The major improvement was the straightening of the <br />channel for about five miles above the bridge and cutting a 200- <br />foot wide pilot channel. In addition, the Colorado Highway <br />~epartment has increased the height of the highway bridge and <br />the A.T.& S.F. railroad has removed the railroad bridge located <br />0.7 miles downstream. <br />One important measure is the completion of construction on <br />Pueblo Dam. The flood-control protection provided will be almost <br />complete for the Arkansas River through Pueblo to Fountain Creek. <br />Downstream from there, the protection will be diminished as the <br />distance increases. The list of drainage areas in table 1 shows <br />that 4,670 square miles of the Arkansas Basin are controlled by <br />Pueblo Dam. This leaves 9,700 square miles of uncontrolled <br />drainage above Las Animas. The flood peak graphs on Figure J <br />indicate that the majority of flood flows since 1942 have origi- <br />nated below Pueblo Dam. In the 1921 flood however, Pueblo Dam <br />would have significantly reduced the downstream floods. <br />The Bureau of Reclamation has an operating agreement with <br />the Corps of Engineers to govern releases from Pueblo Dam during <br />flood conditions. The regulation of flows at Pueblo Dam is <br />intended to keep the downstream flow below the 5,000 cfs capacity <br />of the Arkansas channel. This regulation should allow for a <br />greater attenuation of tributary flood peaks. <br /> <br />8 <br />