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delineated using the flood elevations and two -foot topographic maps at a scale of 1" - 200' made from aerial photographs taken in the fall of 1975 (Reference 2). In cases where the 100 -year and the 500 -year flood boundaries are close together, only the 100 -year boundary has been shown. For the ponds studied by approximate methods, the boundaries of the 100 -year flood were estimated using a U. S. Geological Survey topographic map (Reference 10) enlarged to a scale of 1" - 500' with 10 -foot contour intervals (Exhibit 9). 4.2 Floodways Encroachment on floodplains, such as artificial fill, reduces the flood -carrying capacity and increases flood heights, thus increas- ing flood hazards in areas beyond the encroachment itself. One aspect of floodplain management involves balancing the economic gain from floodplain 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 floodplain management. Unier this concept, the area of the 100 -year flood is divided into a proposed floodway and a flood fringe. For streams, the floodway is the channel cf a stream plus any adjacent floodplain areas that must be kept free of encroachment in order that the 100 -year flood can be carried with- out substantial increases in flood heights. Criteria adopted by the Federal Insurance Administration limits such increases in flood heights to 1.0 foot, provided that hazardous velocities are not produced. In Minnesota, floodplain encroachment is limited by Minnesota Regulations to that which would cause a 0.5 foot in- crease in the flood heights at any point and is, therefore, the briterion adopted for this study. After consultation with representatives of the Minnesota Department Of Natural Resources, responsible city officials have designated floodways for the unnamed tributary to Stubb's Bay. The floodway 17