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<br />, II. DESCRIPTION OF THE BASIN <br /> <br />4. LOCATION <br /> <br />The Platte River and its two major tributar:l.es, the South <br />Platte and North Platte Rivers, comprise the largest tributary <br />system of the Missouri River. The entire basin encompasses <br />88,800 square miles. The South Platte River, lcx,ated mostly in <br />Colorado, and the North Platte River, located mostly in Wyoming, <br />have drainage areas of about 24,300 square miles and 34,900 <br />square miles, respectively. The two streams join near the city <br />of North Platte, Nebraska to form the Platte River. The main <br />stream, located entirely within Nebraska, flows eastward a <br />distance of about 310 miles to its confluence with the Missouri <br />River about 10 miles south of Omaha, Nebraska. <br /> <br />5. PHYS roGRAPHIC FEATURES <br /> <br />The South Platte River and North Platte River basins originate <br />in the high mountainous terrain of the Rocky Mountain range which <br />occupies the western segment of the respective basins. Moving <br />eastward, the features of the basins change from the rougher, <br />steeply sloping terrain of the high plains region to the broadly <br />terraced plains of the lower basin lands. The stream valleys <br />begin as narrow valleys and canyons in the mountainous regions <br />and increase progressively in width tovard the downstream reaches <br />where the two streams join to form the Platte River. Basin eleva- <br />tions range from about 14,200 feet m.s.l. at the Continental <br />'Divide to approximately 2,800 feet m.s.l. at North Platte, and <br />to about 950 feet m.s.L at the mouth of the Platte River. <br /> <br />6. AREA AFFECTED BY FLOODING <br /> <br />a. General. The flooding of May-June 1973 affected a major <br />portion of the South Platte River basin in Colorado. It extended <br />from the metropolitan region of Denver downstream to the Colorado- <br />Nebraska State line. The 16-county disaster area encompassed <br />Adams, Arapahoe, Boulder, Denver, Douglas, Elbert, El Paso, <br />Jefferson, Larimer, Logan, Morgan, Pueblo, Sedgw'ick, Teller, <br />Washington, and Weld Counties. El Paso and Pueblo counties lie <br />within the boundaries of the Corps t Albuquerque District but <br />were assigned to the Omaha District for the duration of the <br />emergency for administrative convenience. Moderate flooding <br />occurred throughout the Nebraska reach of the South Platte River <br />to its confluence with the North Platte River. Flooding on the <br />latter stream in Wyoming vas caused primarily by' snowmelt runoff <br /> <br />4 <br />