FLOOD10000 - Laserfiche WebLink

Home Browse Search

annual flow at Pueblo, The suspended sediment load in the river at Las Animas is about four times that carried by the river at Pueblo. The decrease in flow of the river between Pueblo and Las Animas is due mostly to irrigation withdrawals. The increase in sediment load is produced from tributaries draining areas of high sediment produc- tion. The net effect has been a slow aggradation of the Arkansas River in the vicinity of Las Animas. The Corps of Engineers and local interests, as an emergency measure, have recently straightened the river channel in the vicinity of Las Animas for a distance of about 5 miles. This has somewhat alleviated the aggradation in that reach. 8-07. Effeet of Las Animas projeet.- The Las Animas Local Protection Project will have no appreciable effect on aggradation of the river. The recent straightening of the channel has increased the sediment transport capacity of the river during low flows. The recommended project will have little effect on the sediment transport capacity at high flows. 8-08. SeGUr during design f~od.- The design flood with a maximum discharge of 140,000 c.f.s. will produce maximum velocities of about 26 feet per second in the channel section. Computations of degradation indicate that scour up to 12 feet could be expected in the river channel through the Las Animas project with this flow. A maximum velocity of 25.7 feet per second will occur at the railway bridge. This could cause about 25 feet of scour in the vicinity of the bridge but degradation will be retarded by the shale bed which underlies the river bottom. The shale bed is at a depth of about 10 feet at that location and will limit scour to about that depth. IX - INTERIOR DRAINAGE 9-01. GenepaZ.- The proposed plan of improvement for Las Animas provides for levees on both banks of the Arkansas River. The levee system would create interior drainage problems on both banks of the river that would require provisions for interior drainage facilities. . The right and left bank levees would intercept runoff from subareas of 2,134 and 300 acres, respectively. The right bank drainage area was subdivided into eight subareas. The left bank drainage area was subdivided into three subareas. These subareas are shown on plates 18 and 19. 9-02. Information on areas contributing to interior drainage and drainage patterns of runoff was obtained by field reconnaissance and from data supplied by local interests. This information was confirmed with the U.S. Geological Survey maps, aerial photographs, a map of the storm drainage system for the city of Las Animas, topographic strip- maps along the proposed levee alignments, and recently surveyed cross- sections. 28