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development or revision of existing development in these areas must be approved by the County Commission, and such new or revised development is subject to provisions designed to prohibit: 1. Storage of materials that are floatable or may be detrimental to human, animal, or plant life 2. Disposal of garbage or other solid waste 3. Residential use 4. Creation or deposition of additional debris 5. Placement of fill, installation of structures, or storage of material s that could adversely affect floodflow and possibly cause additional flooding 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 magni tude which are expected to be equaled or exceeded once on the average during any 10-, 50-, 100-, or SOO-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 SOD-year floods, have a 10, 2, 1 and 0.2 percent chance, respectively, of being equaled or exceeded during any year. Although the recurrence interval represents the 10ng- term, average period between floods of a specific magnitude, rare floods could occur at short intervals or even within 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 flood which equals or exceeds the IOO-year flood (1 percent chance of annual exceedence) in any 50-year period is approximately 40 percent (4 in 10); for any 90-year period, the risk increases to approximately 60 percent (6 in 10). The analyses reported herein reflect flooding potent ia1 s based on conditions existing in the community at the time of completion of this study. Maps and flood elevations will be amended periodically to reflect future changes. 3.1 Hydrologic Analyses Hydrologi canal yses were ca rried out to es tabl i sh peak d i scharge- frequency relationships for each flooding source studied by detailed methods affecting the community. In 1985, the COE performed a hydrologic study of the Colorado River for Glenwood Springs to DeBeque Canyon (Reference 10). A hydrology report on the Colorado River dated May 1989, was prepared by J. F. Sato and Associates, Inc. (Reference 11). In this study, the peak discharges for the 10-, 50-, 100-, and 500- year floods on the Colorado River from DeBeque Canyon to the Utah 17