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<br />LAS ANIMAS LOCAL PROTECTION PROJECT <br />LAS ANIMAS, COLORADO, AND VICINITY <br /> <br />DESIGN MEMORANDUM NO. 1 <br />HYDROLOGY <br /> <br />I - INTRODUCTION <br /> <br />1-01. Purpose and scope.- The purpose of this memorandum is to <br />present the basic hydrologic data to be used in the development of the <br />definite project plan for the Las Animas Local Protection Project. <br /> <br />1-02. Drainaqe basin features.- The Arkansas River originates in <br />the Rocky Mountains, near Leadville in central Colorado. From the source <br />to Canon City, Colorado, the stream is a typical mountain torrent, descend- <br />ing from elevation 11,500 to 5,300 feet. This reach of the river is charac- <br />terized by a succession of narrow valleys separated by short canyon sections. <br />Between Canon City and Pueblo, the valley widens slightly and is flanked by <br />foothills as it descends to about 4,690 feet elevation at Pueblo. Here the <br />river emerges into a plains section and the stream is characterized by low <br />banks and a broad sandy bed which shifts frequently. Elevation of the <br />streambed at Las Animas is about 3,900 feet. Stream gradients vary from <br />a maximum of 110 feet per mile in the mountain reaches to about 5 feet per <br />mile at Las Animas. <br /> <br />1-03. Las Animas is located on the south (right) bank of the Arkansas <br />River just above the confluence with the Purgatoire River. The area under <br />investigation comprises 14,417 square miles of the Arkansas River drainage <br />subbasin above Las Animas, Colorado, of which 441 square miles are non- <br />contributing. The area above Canon City has not been conducive to high <br />peak floodflows. For the 77-year period of record the maximum discharge <br />of the Arkansas River at Canon City is 19,000 c.f.s. from a drainage area <br />of over 3,000 square miles. The high plains area below Canon City histori- <br />cally produces peaks of much greater magnitude. Generally there is atten- <br />uation of flood waves between La Junta and Las Animas. This is principally <br />caused by valley storage on the main stem and storage in small reservoirs <br />on the tributary streams of Horse and Adobe Creeks. <br /> <br />1-04. The principal left bank tributaries are Badger, Currant, Oil, <br />Beaver, Fountain, Chico, Horse, and Adobe Creeks. The principal right <br />bank tributaries are Grape, Coal, and Hardscrabble Creeks and St. Charles, <br />Huerfano, Apishapa, and Purgatoire Rivers. Drainage area data are given <br />in table 1. The locations of the watersheds are shown on plate 1. <br /> <br />I-OS. Arkansas River Carrpact Administration. - The Arkansas River <br />Compact is an agreement between the States of Colorado and Kansas defin- <br />ing the right of each State to the wateTs of the Arkansas River stored <br />in John Martin Reservoir. The Compact was signed on 14 December 1948. <br />The Compact was later ratified by the States and consented to by the <br />Congress, becoming effective 31 May 1949. The Compact is admirtistered <br />by three representatives of each State and one Federal representative. <br />