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<br />. hydrometeorology, thereby reducing the uncertainty of design-flood estimates; (4) to determine how to <br />best utilize paleoflood data in flood-frequency analysis and risk-assessment studies for dams and other <br />high-risk facilities; (5) the need to assess the theoretical-maximizing assumptions used to estimate PMP <br />values; and (6) to identify additional benefits from paleoflood investigations to determine the most effective <br />use of reservoir storage, design of other hydraulic structures in floodplains, flood-plain management, and <br />implementation of flood-waming systems, <br /> <br />ADDITIONAL RESEARCH <br /> <br />More quantification (eg., using step-backwater analyses to calculate paleoflood discharges, Wolman <br />pebble counts to calculate particle-size distribution of the bed material, more robust flood-frequency <br />distributions, etc.) would improve the accuracy of individual paleoflood estimates and flood-risk <br />assessment, but was beyond the scope of this study. The interpretation that little out-of-bank flooding <br />has occurred in many thousands of years in northwestem Colorado, including Elkhead Creek, would not <br />differ substantially had detailed hydraulic analysis been done at each site. Although the paleoflood <br />discharge for each stream is slightly less accurate than if a detailed paleoflood reconstruction was made at <br />a site, documenting maximum floods for many streams in a study region provides a more complete <br />assessment of maximum flooding. <br /> <br />. Clearly, use historical accounts of rainfall enhanced flooding need to be thoroughly reviewed and <br />verified as to the actual affect on flood potential in northwestem Colorado. The belief that rainfall <br />substantially increases flood potential, which are not supported by precipitation, streamflow, and <br />paleoflood data, has resulted in large flood estimates used for flood-plain management and dam safety in <br />northwestem Colorado. <br /> <br />CONCLUSIONS <br /> <br />For over 50 years, the design criteria for construction of high-hazard structures such as dams has been <br />the probable'maximum flood (PMF), which is derived from the probable maximum precipitation (PMP). The <br />National Research Council (1994), Hansen and Schwarz (1981), Hansen and others (1988), Jarrett and <br />Costa (1988), and Henz (1991) have recognized the shortcomings of estimating extreme PMP values for <br />high elevations in the Rocky Mountains. Accurately estimating maximum bounds of extreme precipitation <br />and flooding requires conducting sound hydrometeorologic investigations to provide information to help <br />determine the delicate balance between cost and safety. <br /> <br />. <br /> <br />An interdisciplinary paleoflood study was conducted for Elkhead Dam on Elkhead Creek near Craig, <br />Colorado. Elkhead Reservoir is located at an elevation of 6,400 ft in the Colorado Rocky Mountains. The <br />objective of this study was to determine the magnitude of maximum rainfall and flooding that has occurred in <br />and near Elkhead Creek Basin. The melhodology included ensile paleoflood investi9ations Ie determine <br />maximum paleoflood magnitude and regional analyses of extreme precipitation and flood data. The regiOllal <br /> <br />31 <br />