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<br />3.0 FLOODWAY STUDY <br /> <br />3.1 Project Design Flood <br /> <br />This section of the study discusses the various floods that have <br />been routed through the San Miguel River by other' consultants. <br /> <br />In an Environmental Report (ER) on the Uravan Uranium Project <br />prepared by Dames & Moore in August, 1978, the Probable Max'imum <br />Flood (PMF) was considered in an analysis of the Club Ranch Ponds <br />and mill reach of the river. The PMF is the runoff from the <br />tributary area resulting from the Probable Maximum Precipitation <br />(PMP) event, and represents the flood discharge "that may be <br />expected from the most severe combination of critical meteorologic <br />and hydrologic conditions that are reasonably possible in the <br />region." <br /> <br />Although not stated in the ER, the selection of this most severe <br />storm was probably due to an assessment of the Nuclear Regulatory <br />Commission's Regulatory Guide 3.11: "Desi9n, Construction, and <br />Inspection of Embankment Retention Systems for Uranium Mins". <br />This guide discusses the hydrologic analyses required to design <br />a tailing retention system: <br /> <br />Hydrologic Analyses <br /> <br />There will always be some catchment area <br />contributing runoff into the tailing re- <br />tention system. This may vary from the <br />area of the system itself to a substan- <br />tial area incorporating the drainage area <br />of streams entering the valley across <br />which a retention dam is constructed. <br />Substantial runoff volumes and flows can <br />result from heavy precipitation or snow- <br />melt over relatively small catchment areas. <br /> <br />3 <br />