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<br />• 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 rE~gional 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 ~>f 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. Threa discharges <br />were determined, including 50-year and 100-year events, the Probable Maxi- <br />mum Flood and one-half Probable Maximum Flood. The effects of snowmelt <br />runoff were also considered. <br />1D. Hydraulic Analysis - Using these design discharges <br />for operating conditions and for post-mining conditions, thie hydraulic <br />values such as fluty velocity and depth were calculated f~>r the main <br />channel and the areas adjacent to the waste piles. Key item~> 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 moped by these <br />depths and velocities and the duration of water flowing against the piles <br />were estimated. An analysis of the fluvial geomorphologica' 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 />• <br />-5- <br />