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2.2 Community Description The City of Evans is located in central v1eld County, in north- central Colorado. Situated on the South Platte River, Evans borders Greeley on the north and is just across the river from LaSalle. Past u.S. Bureau of the Census data indicate significant growth in Evans since 1940. At that time, approximately 800 people resided in Evans. The populations for 1970, 1972, and 1976 were estimated as 2600, 2800, and 5000, respectively; population projections for 1990 give a population of 6000 people. The corporate limits of Evans include an area of 1400 acres. Evans is currently a residential community, with most of the labor force working in Greeley. There is only limited industry, and most com- mercial activity occurs in Gyeeley (References 1 and 2). The average annual temperature in Evans is 49oF, and the average annual precipitation is 11.8 inches (Reference 3). The South Platte River, which flows in an easterly aud northeasterly direction, forms the southern corporate limits of Evans. In Evans, as in most of Weld County, it flows in a relatively well-defined channel of approximately 300 to 600 feet in width and 6 to 8 feet in depth. The channel is typically braided and is situated in a broad, shallow flood plain ranging in width from approximately 3000 feet to 5000 feet. Its sandy streambed slopes at approximately 7 feet per mile in Evans~ The flood plain cover is cottonwood trees near the banks and row crops and pastureland elsewhere. A gravel mining operation, as well as some residential acreage, exists on the Evans side of the South Platte River flood plain. The primary underlining soils types in Evans are of the Fluvaquents- Fluvents Association. These soils are typically warm, deep, and poorly drained (Reference 4) ~ 2.3 Principal Flood Problems Flooding along the South Platte River in Evans normally occurs from May to August, with the most frequent flooding occurring in June. Floodwaters can result from either intense, localized rainfall, like the 1965 flood, or general rainstorms lasting several days, like the 1969 and 1973 floods. Both of these types of floods may be augmented by snowmelt. Past floods on the South Platte River at Evans occurred as follows: in May 1876; in late May and early June 1894; in June 1914; in June 1921; from August 30 to September 4, 1938, in April and tlay 1942; from mid-May to late-June 1949; in early May 1951; in June 1965, in early May 1969; and, in early May 1973. Some of the significant floods and peak discharges recorded at the Kersey gage, just a few miles downstream from Evans, are shown on page 4 (Reference 5). 3