Laserfiche WebLink
<br />elevation. Steel jetties will be used for levee protection in loca- <br />tions where flows indicate that protection is necessary. Profiles <br />of design water surface elevations, levee design elevations, and lo- <br />cations of levee protective works are shown on plates 18 and 19. A <br />tabulation of project design flow data for preproject and postproject <br />conditions is presented on plate 19. Typical levee sections are <br />shown on the project map, plate 20. <br /> <br />7-02. U.S. Highway 50 bridge.- Subsequent to the project docu- <br />ment studies the U.S. Highway 50 crossing of the Arkansas River has <br />been replaced by a new structure that has been designed with sufficient <br />capacity to pass the design flow with.about three feet of clearance. <br /> <br />7-03. AT&SF Rai~y bridge.- In order to provide an adequate <br />waterway opening for the design flow and to maintain existing railroad <br />grades, it will be necessary to alter the existing bridge of the branch <br />line crossing the Arkansas River at Las Animas. The girders of the ex- <br />isting bridge are about 9 feet deep and obstruct channel flow for dis- <br />charges of design flood magnitude. A redesign of the girder portion <br />of the bridge, to increase the length to 550 feet and to raise low <br />steel about 6 feet, will provide about 3 feet of clearance above the <br />design water surface. <br /> <br />7-04. OVerbank oZearinq.- The overbank will be cleared to main- <br />tain an '~" value of 0.035 at the highway and railway bridges. With <br />this clearing, there will be a flow width of 830 feet at the highway <br />bridge and 858 feet at the railway bridge. Overbank clearing will be <br />maintained between the bridges so that the cleared width plus the <br />channel width will be in accord with the widths at the bridges. The <br />width of clearing will be transitioned to natural conditions upstream <br />from the highway bridge and downstream from the railway bridge. <br /> <br />7-05. Coincident ]1ow.- Backwater studies were made to deter- <br />mine the adequacy of the levee at the downstream end of the project. <br />The recurrence interval of a discharge of 140,000 c.f.s. on the Arkansas <br />River at Las Animas with Pueblo Dam operating is 143 years. For a com- <br />parable recurrence interval the flow on the Purgatoire River at Las <br />Animas with Trinidad Dam operating is 102,000 c.f.s. To determine the <br />water surface profile for the project design flow, a flow of 20,000 <br />c.f.s. in the Purgatoire River was assumed to coincide with the project <br />design flow of 140,000 c.f.s. in the Arkansas River. Conversely, it <br />was assumed that a flow of 8,000 c.f.s. in the Arkansas River would <br />coincide with the flow of 102,000 c.f.s. in the Purgatoire River. <br /> <br />7-06. HydroZogio faoiZities.- The existing network of precipi- <br />tation and stream gaging stations in the Arkansas River subbasin above <br />Las Animas is adequate to provide warning.of impending flood conditions <br />and to supply data for hydrologic studies of storms and floods. Bene- <br />fits which would accrue to the Las Animas Local Protection Project will <br />be based on flows measured at the existing stream gaging station on the <br />Arkansas River at Las Animas. This gage is an integral part of the <br /> <br />26 <br />