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In 1971 Littleton voted to provide local funds to assist in acquiring land for a non-structural flood control plan. In 1984 the City acquired and annexed approximately 625 acres encompassing the lOO-year floodplain boundaries of the South Platte River, in the southern portion of Littleton (References 8 and 9). This area, known as the Littleton Flood Plain Park, extends approximately 2 miles north of the Arapahoe-Douglas County 1 ine and allows the rural open space of the area to be retained. In 1988, immediately downstream of the Littleton Flood Plain Park, the COE completed the installation of a 4-mile channel improvement project, from below West Oxford Avenue upstream to Fairway Lane. State and local funds were also utilized in carrying out this channel improvement project that was designed to contain the 100- year flood discharge. In an effort to control development and use of floodplain lands, the Ci ty, in 1971, adopted a floodplain zone that overlays the other City-designated land use zones. This zoning ordinance requires strict compliance, and designates appropriate measures to be taken to alleviate potential flood damage where a flood hazard exists. No major structural improvements have been undertaken by the City on the other tributaries that pass through the city. Minor improvements have been made on both Slaughterhouse Gulch and Li t t le' s Creek in an effort to minimize damage and flooding from more frequent flood events. Major drainageway planning reports have been completed for Slaughterhouse Gulch, the South Tributary to Slaughterhouse Gulch, and Big Dry Creek, as they pass through Littleton. These reports designate various structural measures and non-structural actions that would be appropriate to alleviate potential flood damage from these streams. 3.0 ENGINEERING METHODS For the flooding sources studied by detailed methods in the community, standard hydrologic and hydraulic study methods were used to determine the flood hazard data required for this study. Flood events of a magnitude which are expected to be equaled or exceeded once on the ave~age during any 10-, 50-, 100-, or 500~year period (recurrence interval) have been selected as having special significance for floodplain management and for flood insurance rates. These events, commonly termed the 10-, 50-, 100-, and SOO-year floods, have a 10-, 2-, 1-, and O.2-percent chance, respectively, of being equaled or exceeded during any year. Al though the recurren:ce interval represents the long-term average period between floods of a specific magni tude, rare floods could occur at short intervals or even wi thin the same year. The risk of experiencing a rare flood increases when periods greater than 1 year are considered. For example, the risk of having a 9