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The rolling high sparsely vegetated. high plains region is plains terrain is fairly rough, broken, and The predominant vegetation for this semi-arid sage brush, cactus, and native grass. Flows in the arroyo are the result of snowmelt and rainfall runoff during the winter and early spring. During the summer months, the flows result from thunderstorms or general rains over the entire watershed. Floods in the study reach normally originate from runoff of the entire watershed due to the extent of the drainage. The steep slopes and long narrow shape of the drainage are conducive to fast rises and high peak flows of short duration. The average slope is approximatelj 109 feet per mile in the watershed, and only 63 feet per mile within the study reach. Streambed elevations within the study reach vary from approximately 4,708 feet at the mouth to 4,868 feet at the upstream limit of study (Reference 5). The rural used for currently potential areas of Pueblo are dominated by irrigated and dry land farming and ranching. Natural resource activities are focused on sand, gravel, and clay extraction, with the for limestone extraction. According to the 1980 U. S. Census, the total population of Pueblo County in 1980 was 125,972 compared to a population of 118,238 in 1970. The City of Pueblo, the county seat, is by far the largest city in Pueblo County, having a population of 101,686 in 1980 (Reference 6). The climate in central and eastern Pueblo County is semi-arid with an average annual precipitation of about 12 inches. The vegetation is predominantly sage brush, cactus, and native grass which is typical of the semi-arid high plains. The more mountainous southwestern region has an average annual precipitation of 20 to 24 inches. The vegetation includes pine, fir, and spruce trees along with typical mountain grasses (Reference 1). 2.3 Principal Flood Problems Analysis of climatological data and inspection of the flood history show that the most severe flood-producing storms occur during the late spring or summer months. The spring season is the transitional period between the occurence of instability and frontal activity and is subject to storms caused by both types of activities. This may result in heavy spring snow storms in the higher elevations or high intensity rains over the plains region. These storms and the physical features of the area can produce the rapid concentration of runoff that characterizes flash floods of high peak flows, small volumes, and short duration (References 1, 2, 3, 4, and 5). 7