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Flood boundaries have been reconciled with previous studies on BiSj Dry Creek (Reference 4), Little Dry Creek (Reference 20), Clear Creek (Reference 19), and the South Platte River (References 2, 3" and 10). ~ For streams studied by approximate methods, the boundaries of the 100-year flood were delineated using the determined elevations and topographic maps (Reference 24), and were reconciled with u.s. Geo- logical Survey Flood Prone Area Maps (Reference 22), and concurrent studies being done on Second and Third Creeks for the Urban DrainaSje and Flood Control District (Reference 7). The boundary of the 100- year flood for Hidden Lake was taken from the Urban Drainage and Flood Control District study for that drainage system (Reference 9). Small areas within the flood boundaries may lie above the flood elevations and, therefore, not be subject to flooding; owinSj to limitations of the map scale, such areas are not shown. 4.2 Floodways i' Encroachment on flood plains, such as artificial fill, reduces the flood-carrying capacity and increases flood heights, thus increasing flood hazards in areas beyond the encroachment itself. One aspect: of flood plain management involves balancing the economic Sjain from flood plain development against the resulting increase in flood hazard. For purposes of the Flood Insurance Program, the concept of a floodway is used as a tool to assist local communities in this aspect of flood plain management. Under this concept, the area of the 100-year flood is divided into a floodway and a floodway fringe. The floodway is the channel of a stream, plus any adjacent flood plain areas, that must be kept free of encroachment in order that the 100-year flood be carried without substantial increases in flood heights. As minimum standards, the Federal Insurance Administration limits such increases in flood heights to 1.0 foot, provided that hazardous velocities are not produced. The floodways used in this report are defined in the Adams County Zoning Regulations (Refer- ence 25), 1975. The floodway was approved and adopted by the County Commissioners as: "That area of the flood plain required for a reasonable passage or conveyance of the 100-year flood which is characterized by flows of 2 feet per second or more, for depths of 18 inches or more, and/or which will convey the flood flows with not more than 0.5-foot rise in the water-surface elevation based on the assumption that there will be an equal degree of encroachment extended for a significant segment on both sides of the water course." .ol 18 .