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I I I I I I I I I I I I I I I I I I I B-1 INTRODUCTION The design criteria utilized for this master plan are based on those con- tained in the Denver Regional Council of Governments' Urban Storm Drainage Criteria Manual (Reference 32). rlowever, due to the steep gradient, 1 arge size bed material, and the bridge structures at Ford Street and Washington Avenue, exceptions have been made with regard to allowable overbank depth and average velocity. Specific planning and design criteria applicable to Clear Creek - Youngfield through Golden are the following: 1. GRASS-LINED CHANNELS. Design will generally be based on channels having natural waterway hytlraul ic and appearance characteristics. They should be aesthetically designed toi;he local environment and should provide multi purpose benefits such as recreational uses where appl icable. Specific criteria include: APPENDIX B RECOMMENDED STRUCTURAL CRITERIA FOR CLEAR CREEK - YOUNGFIELD THROUGH GOLDEN o 100-year design overbank depths would be approximately 10 feet in the vicinity of Ford Street and Washington Avenue, and \\Ould average be- t\\een 5 and 7 feet upstream to U. S. 6. o A max imlJ11 aver age des i gn velocity of 8.0 to 12.0 feet per second (fps) for the lOO-year storm. Riprap protection would be required at critical areas such as the toe of slopes. o 4:1 channel side slopes, however, where develor:ment exists and right- of-way is a problem, the slopes may be 3:1. A 2: 1 slope must be sta- bil ized by riprap protection. o Freeboard no 1 ess than 1. 0 foot. o Grass cover chosen for hytlraul ic retardance, i.e., resistance to scour forces, and ease of maintenance. o The low flow channel would be sized to carry the average spring snow- melt flow, or approximately 800 cfs. The existing channel width, averaging between 60 and 65 feet, generally affords this capacity at a depth of about 2 feet.