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Flood water elevations in the West Fork of Clear Creek and Lion Creek are often unstable due to the very high stream velocities. Another complicating factor is the possibi i ity of debris collection at bridges obstructing flows. This is a concern because of the heavi Iy forested area above Empi reo Although this possibi I ity exists, especially at the smaller bridges on Lion Creek, any attempt to include it in the analysis would be speculative. Therefore, the flood elevations as shown on the profi les are valid only if hydraul ic structures in general remain unobstructed. 4.0 LAND USE APPLICATIONS A prime purpose of the National Flood Insurance Program is to en- courage state and 'Iocal governments to adopt sound flood plain manage- ment programs. Each flood insurance study, therefore, includes a Flood Boundary and Floodway Map (Exhibit 2) designed to assist communities in developing flood plain management measures that wi I I provide the best use of their flood plain lands. 4.1 Flood Boundaries In order to provide a national standard without regional discrim- ination, the lOa-year flood has been adopted by the Federal Insurance Administration as the base flood for purposes of flood plain management measures. The SOO-year flood is employed to indicate additional areas of flood risk in the community. For each stream, the boundaries of the lOa-year and the SOO-year flood have been delineated using the flood elevations determined at each cross section: between cross sections, the boundaries were extrapolated using topographic maps at a scale of I :24,000 with a coutour interval of 40 feet (Reference 17). In cases where the lOa-year and the SOO-year flood boundaries are close together, only the lOa-year boundary has be~n shown. Areas subject to shal low flooding where a clearly defined channel does not exist and where the path of flooding is unpredictable and indeterminate are included in Zone B on Exhibit 3. Smal I areas within the flood boundaries may lie above the flood elevations and therefore not be subject to flooding; owing to I imitations of topographic information and the map scale, such areas are not shown. 4.2 Proposed F100dways Encroachment on flood plains, such as artificial fi I I, reduces the flood-carrying capacity and increased flood heights, thus increasing flood hazards in areas beyond the encroachment itself. One as- pect of flood plain management involves balancing the economic 10