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I I I I I I I I I I I I I I I I I I I g IV. FLOODPLAINS and (4) provide for the preservation of floodways and floodplain storage areas in order to protect those downstream from increased flooding. Flood Frequency Flood P rofi 1 es Federal and State flood damage mitigation efforts, including the Flood Insurance Act of 1968, the Flood Disaster Protection Act of 1973, the Water Resources Development Act of 1974, and the State of Colorado Model Floodplain Regulation, and City and County of Denver Floodplain Regulation are all aimed at avoiding the floodplain occupancy mistakes of the past. The Master Plan drawings were presented to illustrate means of minimizing flood hazards and flood damages. Improvements made to the drainageway for a flood frequency of less than the 100- year event should have the residual floodplain regulated. Floodplains formed by storm water runoff are a natural process, the floodplains cannot be used for any human occupied structures without costly can- pensatory control measures. Developers and governi ng agenci es shoul d plan the use of the floodplain wisely. For existing human occupied structures inside the floodplain, flood insurance is encouraged to minimize the flood losses. The State of Colorado, Urban Drainage and Flood Control District and City and County of Denver, consider the 100-year frequency flood as the fl ood event to be used in des i gni ng and protect i ng structures and dwell ings for human occupation. Therefore, all floodplain regulations are based upon the 100-year flood. The 100-year flood occurs, on the average, once in a 100-year period, and has a one percent chance of being equaled or exceeded in any given year. The rates for the 2-, 5-, 10-, 50-, and 100-years flood frequencies have been determined and presented in Chapter III for future develop- ment condition. The water surface profiles were computed using the HEC-2 backwater program developed by the United States Army Corps of Engineers. Digitized channel cross-sections were obtained from aerial photos and checked against topographic mapping with 2-foot contour, 1- inch to 100-foot scale. Roughness coefficients and hydraulic struc- tures (culverts and bridges) were evaluated based on field investigation and field survey information. Flood plain mapping and floodway data were submitted to the District in the form of a Flood Hazard Area Delineation Report dated February 1979. The.floodplain mapping can be used for flood control and land use planning purposes. The laO-year flood plain for future develop- ment conditions with existing channel conditions is al so del ineated in the drawings presented at the end of this report. Floodplain Management The purpose of floodplain management is to: (1) protect the public's health, safety and general welfare; (2) el iminate or minimize flood hazards and flood damages; (3) promote the wise use of the floodplain;