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. . . . -" . \ l'j (,'... PART II--GENERAL DESCRIPTION The Narrows Unit area in northeastern Colorado comprises approximately the downstream half of the South Platte River Basin in Colorado. The upstream half of the basin originates along the Continental Divide at elevation approaching 14,000 feet. That area provides most of the water supply of the basin from native supplies and from trans- mountain importations. TIle basin slopes to the east and merges into the Colorado Piedmont area in which the Narrows Unit is located. The South Platte watershed through the Piedmont section is a broad rolling plain through which the river has formed a wide valley of flood plains and bench lands on river terraces. The bench lands are situated some 20 to 200 feet higher than the flood plains. The river has a gradient of 8 to 10 feet per mile. Geologically, the Colorado Piedmont section is classified as late mature or old with outcroppings of shales and sandstones of the Pierre formation. The: two most important South Platte River tributaries of con- cern to the Narrows Unit are Kiowa and BijOu Creeks. Both tributaries enter the river from the south. Both tributaries flow through areas of poorly consolidated sediments and, during periods of high runoff, contribute considerable ~tmntities of sediment to the river. Kiowa Creek flows into the river Within the Narrows Reservoir site. Bijou Creek, however, empties into the river immediately downstream from the Narrows Darn site. NUlllerous other tributaries, mostly intermittent, enter the South Platte River from both the north and souttl in the reach between Narrows Reservoir and the Colorado-Nebraska boundary. CLIMATE The unit area has a temperate clirrate with weather character- istics similar to those of' the Western Great Plains. The region is normally semiarid, although precipitation varies widely from year to year. Precipitation and temperatures are influenced by the great air nasses and weather fronts wllich periodically sweep across t.he Great Plains Province. The temperate climate, wrLLch is accompanied by abundant sunshine with warm days and cool nights during tj-,e growing season, makes the area especially favorable for agriculture and its associated industries. Although the natural precipitation is adequate to support only highly speculative dryland farming and livestock grazing, a wide variety of crops with high yields may be grown when irrigation water is sufficient. 5