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<br />The climate of the area is semi-arid to arid. Precipitation <br />in the area varies from a mean annual precipitation of <br />12 inches in Florence to a mean annual precipitation of <br />20 inches in the mountains south of Florence. The temperature <br />in the study area varies from a mean minimum of 200F in <br />January to a mean maximum of 900F in July. <br /> <br />2.3 Principal Flood Problems <br /> <br />While slopes are steeper in the upper drainage basins, the <br />dense vegetation in these areas serves to reduce rainfall <br />runoff. A greater percentage of runoff is permitted by the <br />sparse vegetation of the foothills and pasture land at the <br />lower elevations. Consequently, the maj ority of the flood <br />problems in the study area are caused by cloudburst-type <br />storms over the foothills to the south which usually occur <br />during the summer months of June, July, and August. <br />Characteristic, of this type of flooding is a high intensity, <br />short duration rainstorm of limited areal extent, resulting in <br />a flash flood of high peak flow, short duration, and total <br />runoff volume. <br /> <br />Flood potential also exists from long duration rain storms and <br />from rapid melting of snow cover in the upper drainage basins <br />during late spring. These type of floods are characterized by <br />moderate peaks, large volumes, and long duration. The <br />potential for the most severe flooding is created by the <br />combination of rapid snowmelt with long duration rainfall. <br /> <br />Detailed information on floods before the turn of the century <br />is very limited. Information on past flooding is based on <br />newspaper accounts and interviews with longtime residents of <br />the area. Large floods occurred at Florence in 1909, 1921, <br />1932, 1941, 1948, 1949, and 1965. These floods have caused <br />major damage, disrupting highway and railroad traffic and <br />communication services, drowned livestock, destroyed <br />agricultural lands, roads, bridges, and buildings. Several <br />persons have lost their lives and others have been injured <br />(Reference 2). <br /> <br />The flood of June 1921 is considered the most severe flood <br />known in Florence. A total of 6.9 inches of rain fell in <br />Florence from June 3 through June 6. The area in the hills <br />south of Florence had experienced days of low intensity <br />rainfall saturating the ground. Then on June 5, a cloudburst <br />fell on the Coal Creek drainage area and the runoff hit the <br />city as a 4- to 6-foot wall of water. Peak discharges have <br />been estimated by the USGS (U.S. Geological Survey) at <br />2,760 cubic feet per second (cfs) for Oak Creek and 3,720 cfs <br />for Coal Creek. Damages were estimated at up to a quarter of <br />a million dollars and 16 lives were lost in the City of <br />Florence. Floods in 1909 and 1932 were characterized by <br />high-intensity cloudbursts, while the floods in 1941, 1948, <br />1949, and 1965 were caused by high-intensity cloudbursts, <br />coupled with hail choked runoff channels. <br /> <br />- 3 - <br />