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Post Flood Assessment Report 2 Chapter 1 - Introduction Draft Revised 01/05/01 I I I I I I I I I I I I I I I I I I I main stem on the south bank. These three rivers are small perennial streams in their mountainous headwater reaches, but as they progress: through the foothills to the rolling plains, the base flows are depleted by diversions for irrigation. The river channels widen with poorly defined banks and low flow channels meander through the valleys. The Huerfano River confluence is at Boone about four miles south of Avondale. The Apishapa River confluence is just downstream of Fowler. The Purgatoire River confluence is just south of Las Animas. Three smaller tributaries are the St. Charles River, Timpas Creek and Horse Creek. The St. Charles River enters the Arkansas River from the soqthjust downstream of Pueblo. Timpas Creek enters from the south at Swink, about four miles downstream of Rocky Ford. Horse Creek, enters from the north just upstream of Las Animas. The permeability of the soil and the absence of well-defined watercourses in these tributatY watersheds tend to reduce the runoff. Surface water discharge into the main stem is minor except in cases of extreme precipitation. Timpas Creek has a drainage area of 496 square miles. Watershed elevations extend from 5,400 feet at the headwaters to 4,120 feet at the stream gage near Swink. Horse Creek has a drainage area of 1,403 square miles. The elevation of the Horse Creek watershed ranges from 6,600 feet to 4,200 feet. There are no significant flood control stmctures on these tributaries. The St. Charles Reservoir is just south of Pueblo, but it is not actually on the St. Charles River. The State of Colorado has identified flood prone areljs in 267 cities and towns among all of its 63 counties. There are over 250,000 people living in floodplain areas of the state. The value of property, structures, and contents located in identified floodplains is estimated to be over $11 Billion (1996 state estimate). Based on property damage data from 1896 to 1984, the average annual flood losses in Colorado are estimated to be $17,600,000. Cumulative flood losses for the most damaging floods in Colorado between the turn Of the century and 1993 include 331 people killed and $3.3 Billion (1995 state estimate) worth of property damage. United States Presidents have declared a major flood disaster within Coloradq in 9 out of the last 32 years between 1965 and 1999 (1965, 1969, 1970, 1973, 1976, 1982, 1984, 1997, and 1999). FLOOD OF APRIL 29, 1999 A large regional storm produced heavy rainfall in southeast Colorado and northeast New Mexico from Thursday April 29, 1999 through Sunday May t, 1999. Localized flooding occurred throughout the region. Numerous roads and bridges ;were flooded or damaged. Homes were flooded in Fountain/Manitou Springs beginning on the evening of April 29, 1999. The unusually large volume of runoff produced by the storm resulted in more erosion damage along Fountain Creek than any previous flood. The Arkansas River began flooding on April 30, 1999 affecting homes east of Pueblo near Avondale. The flood reached a new stage of record at Avondale on May 1, 1999. Between May 1 and 2, 1999 floodwaters spread downstream affecting homes in Rocky Ford and La Junta. Las Animas was spared damage to homes. Trinidad Dam on the Purgatoire River and John Martin Dam on the Arkansas River both rose to new record pool reservoir elevations. On May 17, 1999, the President signed DR#1276 declaring the ten counties of Otero, Bent, El Paso, Larimer, Pueblo, Las Animas, Crowley, Kiowa, Elbert, and Preemont in Colorado eligible for Federal Disaster Assistance.