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, , DESCRIPTION OF STUDY AREA At the time this study was initiated, the flow paths were not all known. As a result of these investigations, it was determined that a segment of flow will move to the vicinity of Atwood. Mapping was not done in this area; therefore, specific details of flow depth, etc. were not made for this segment of flow. Another significant segment of flow departs from the channel at a location just below County Road 33. The flow moves overland away from the main channel towards the northeast and eventually to the vicinity of the Riverside Cemetery. Water surface profiles were not computed for this reach because of the unpredictable meandering flow pattern through farmland; however, a probable flow path was sketched on the flood plain maps. Natural and Beneficial Flood Plain Values The flood plain along Pawnee Creek, within the study limits. generally contains cottonwoods and willows along the channel. irrigated cropland adjacent to the channel, and grasslands interspersed with the cropland. The channel does a considerable amount of meandering which enhances the visual aesthetics and wildlife habitat values in the area. . h .. Bas~n C aracter~st~cs Pawnee Creek drains an area of approximately 645 square miles above U.S. Highway 6 near Atwood, see Fig 1. The basin inCludes areas in Logan as well as Weld Counties. The mouth of Pawnee Creek is located several miles southwest from Sterling along U.S. Highway 6 and the Burlington/Union Pacific Railroad tracks. The elevation of Pawnee Creek at this location is about 3980 ft above sea level. The elevation of the upper end of the basin is near 5400 ft. The well-known Pawnee Buttes are in the upper reaches of the basin at an elevation of about 5375 ft. The major tributaries to Pawnee Creek are Raymer Creek, South Pawnee Creek with its tributary wildhorse Creek, North Pawnee Creek with its tributary Igo Creek, Cottonwood Creek, Horsetail Creek, and Spring Creek. These streams are basically intermittent with some accumulations of live water, particularly in South Pawnee Creek. The soils in the basin are predominantly loarns and clay loarns, with sandstone, shale, and siltstone outcroppings. They fit primarily in hydrologic groups "e" and."B". Hydrologic curve, numbers are in the range of 77 to 79 w~th the pr~mary vegetat~on being native range with some winter wheat and a significa~t amount of irrigated cropland in the lower part of the bas~n. The mcan annual precipitation for the basin ranges from 14 to 16 inches. The mean annual precipitation for Sterling, nearest town with weather data, is 14.96 inches with a medn dnnual temperature of 46.5 degrees Fahrenheit. i I. i The flood plain supports a variety of wildlife species such as: cottontail, squirrel, prairie rattlesnake and a variety of birds including the burrowing owl, Swainson's hawk, prairie falcon, meadowlark, horned lark, lark bunting, and pheasant, Notable predators include the great horned owl, bald and golden eagle, coyote, kit fox, badger, and skunk. White-tailed and mule deer and antelope are common to the area. In the fall and sprinq. multitudes of migratory birds pass over Logan County. StUdY Limits The area of intercst in this study includes locations where flood waters from Pawnee Creek damage farm lands and county roads along the lower reaches of the basin. Also of concern is Pawnee Creek overflow which inundates portions of the City of Sterling. Since this basin is so large, the study limit was confined to the lower reach trom county Road 29 to V.S. Highway 5. The total study length is about 7.6 miles whiCh includes the main stem of Pawnee Creek and the overflow area between Pawnee Creek and the Riverside Cemetery along U.S. Highway 6. A number of out-of-bank conditions occur with segments of flood waters departing overland away from the main channel. It was attempted h7rein t? track these floodwaters to locations where they comb~nc aga~n and pose a flood threat to the Town of Sterling.