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7. Review Recent Research - Recent research and studies in <br /> the flood hydrology of Colorado mountain and foothill streams were <br /> reviewed. Agencies contacted included the Denver Water Department, <br /> NOAA and the U.S. Geological Survey. These studies included a spring <br /> snowmelt analysis as well as the thunderstorm type of runoff event. <br /> Streamflow records for the Coal Creek gaging station and regional cor- <br /> relation were used to analyze the snowmelt runoff frequency for Ralston <br /> Creek. <br /> 8. Determine Design Criteria - A meeting with the MLRD staff <br /> was held to discuss the hydrologic methods and recurrence interval for <br /> flood flows that is considered acceptable for design of operational and <br /> long-term hydrology. During the meeting, the current state of knowledge <br /> of streambed morphology of mountain streams as it relates to the Ralston <br /> Creek watershed was also reviewed. <br /> 9. Determine Design Discharge - Using the methodology and <br /> recurrence interval acceptable to the MLRD staff, storm hydrographs and <br /> peak discharge rates for design were calculated. Three discharges <br /> were aetermined, including 50-year and 100-year events, the Probable Maxi- <br /> mum Flood and one-half Probable Maximus Flood. The effects of snowmelt <br /> runoff were also considered. <br /> ill. Hydraulic Analysis - s ng these design discharges <br /> for operating conditions and for post-mining conditions, the hydraulic <br /> values such as flow velocity and depth were calculated for the main <br /> channel and the areas adjacent to the waste piles . Key items determined <br /> included the depth and velocity of water against the toes of the waste <br /> rock piles. The size of waste rock material which can be moved by these <br /> depths and velocities and the duration of water flowing against the piles <br /> were estimated. An analysis of the fluvial geomorphological character- <br /> istics of the site was made to assess the tendency of the streambed <br /> for degradation, aggradation or lateral migration in the vicinity of <br /> the piles. <br /> - 5 - <br />