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• Coal Canyon <br />Scour Protection and Transition Zone <br />Calculation Rational and Results Summary <br />Rational: <br />Calculated using SEDCADT"" 4 for Windows <br />100 Year Peak Flow of 965 CFS from pages Misc-13 through 18. <br />The Coai Canyon Channel is 40-feet wide. Since SEDCAD wil4 only model a 20- <br />foot wide channel, one-half of the peak flow (482.5 cfs) is used in the <br />calculations. <br />Scour protection is provided below the outlet of the two large culverts under haul <br />road No. 4. The SEDCAD model assumed a 2.5% slope. Results indicated a <br />DSo rip-rap size of 21-inches. Appropriate geotextile fabric will be installed under <br />the rip-rap. Rip-rap will be installed approximately 3-feet under the culverts and <br />extend approximately 15 downstream for a total length of about 18-feet. Rip-rap <br />will be keyed into the channel about 18-inches deep. At the downstream end a <br />smooth transition will be made between the dirt channel and the rip-rap. <br />• <br />The transition zone provides for an elevation drop in the channel of about four <br />feet in sixteen feet. The SEDCAD model used a 25% slope. Results indicated a <br />Dso rip-rap size of 30-inches. Appropriate geotextile fabric will be installed under <br />the rip-rap. Rip-rap will be keyed into the channel about 24-inches deep at both <br />upstream and downstream ends. The 30-inch rip-rap will be bedded on a 6-inch <br />thick layer of well graded pit run gravel. <br />See Exhibits 8B, & 55. <br />ENGINEER'S CERTIFICATION <br />The SEDCAD calculat~gr~ r information presented on pages Misc-20 through Misc- <br />22 were prepared boy,~~ month of May 2003, and the information presented <br />is true and correct=best~o~'m~knowledae and belief. <br />~,,~ James E.,$t4ver, P.E. Date <br />;~e~ istered F,rf'~sional Engineer <br />~.~~e•oficado No. 19230 <br />e NAL • <br />•oca~• <br />• Misc-20 (New 5/03) <br />